DOS AND THE IBM PC

** Programmer's Technical Reference for MSDOS and the IBM PC **

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ISBN 1-878830-02-3 (disk-based text)

C H A P T E R O N E

DOS AND THE IBM PC

C O N T E N T S

Some History .......................................................... 1**1

What is DOS? .......................................................... 1**2

Other Operating Systems ............................................... 1**3

Specific Versions of MS/PC-DOS ........................................ 1**4

The Operating System Heirarchy ........................................ 1**5

DOS Structure ......................................................... 1**6

DOS Initialization .................................................... 1**7

SOME HISTORYÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**1

Development of MSDOS/PCDOS began in October 1980, when IBM began searching

the market for an operating system for the yet-to-be-introduced IBM PC.

Microsoft had no 8086 real operating system to sell, but quickly made a deal

to license Seattle Computer Products' 86-DOS operating system, which had been

written by Tim Paterson earlier in 1980 for use on that company's line of 8086,

S100 bus micros. 86-DOS (also called QDOS, for Quick and Dirty Operating System)

had been written as more or less a 16-bit version of CP/M, since Digital

Research was showing no hurry in introducing CP/M-86.

This code was quickly polished up and presented to IBM for evaluation. IBM

had originally intended to use Digital Research's CP/M operating system, which

was the industry standard at the time.

Folklore reports various stories about the rift between DRI and IBM. The most

popular story claims Gary Kildall or DRI snubbed the IBM executives by flying

his airplane when the meeting was scheduled. Another story claims Kildall

didn't want to release the source for CP/M to IBM, which would be odd, since

they released it to other companies. Industry pundit Jerry Pournelle claims

Kildall's wife killed the deal by insisting on various contract changes. I

suspect the deal was killed by the good ol'boy network. It's hard to imagine

a couple of junior IBM executives giving up when ordered to a task as simple

as licensing an operating system from a vendor. Wouldn't look good on their

performance reports. It would be interesting to hear IBM's story...

IBM found itself left with Microsoft's offering of "Microsoft Disk

Operating System 1.0". An agreement was reached between the two, and IBM agreed

to accept 86-DOS as the main operating system for thir new PC. Microsoft

purchased all rights to 86-DOS in July 1981, and "IBM Personal Computer DOS

1.0" was ready for the introduction of the IBM PC in October 1981. IBM

subjected the operating system to an extensive quality-assurance program,

reportedly found well over 300 bugs, and decided to rewrite the programs. This

is why PC-DOS is copyrighted by both IBM and Microsoft.

Some early OEM versions of DOS had different names, such as Compaq-DOS, Z-DOS,

Software Bus 86, etc. By version 2 Microsoft managed to persuade everyone but

IBM to refer to the product as "MS-DOS."

It is sometimes amusing to reflect on the fact that the IBM PC was not

originally intended to run MSDOS. The target operating system at the end of the

development was for a (not yet in existence) 8086 version of CP/M. On the other

hand, when DOS was originally written the IBM PC did not yet exist! Although

PC-DOS was bundled with the computer, Digital Research's CP/M-86 would probably

have been the main operating system for the PC except for two things - Digital

Research wanted $495 for CP/M-86 (considering PC-DOS was essentially free) and

many software developers found it easier to port existing CP/M software to DOS

than to the new version of CP/M.

The upgrade from DOS 3.3 to 4.0 was done in-house by IBM. DOS 4.0 was a

completely IBM product, later licensed back to Microsoft. In early 1990 IBM

announced that it was ceasing development of DOS and all further work would

be done solely by Microsoft.

Microsoft Press' "MSDOS Encyclopedia" shows a reproduction of a late

DOS 1.25 OEM brochure. Microsoft was touting future enhancements to

1.25 including Xenix-compatible pipes, process forks, and multitasking,

as well as "graphics and cursor positioning, kanji support, multi-user

and hard disk support, and networking." Microsoft certainly thought

big, but, alas, the forks, multitasking, and multiuser support never

came about, at least in US versions of DOS. Oddly, the flyer claims

that

"MS-DOS has no practical limit on disk size. MS-DOS uses 4-byte XENIX

OS compatible pointers for file and disk capacity up to 4 gigabytes."

Umm... yeah. One sort of gets the idea nobody at Microsoft had a hard

disk larger than 32 megabytes...

For the record they actually delivered:

Xenix-compatible pipes DOS 2.0 ("|" operator)

process forks, and multitasking eDOS 4.0 (not delivered in the US)

multi-user never delivered

graphics and cursor positioning DOS 2.0 (ANSI.SYS, more than likely)

kanji support DOS 2.01, 2.25 (double-byte char set)

hard disk support DOS 2.0 (subdirectories)

networking DOS 3.1 (file locking, MS Networks)

Early Microsoft ads pumped DOS' Xenix-like features and promised Xenix

functionality in future releases.

We'll probably never know what the real story was behind eDOS/DOS 4/

DOS 5/286DOS/OS2. Microsoft had announced their intent to build a

multitasking, multiuser version of MSDOS as early as 1982. They shipped

betas of "DOS 4.0" in '86 and early '87, before 3.3 was even announced.

Microsoft UK announced they had licensed 4.0 to Apricot Computer, and

the French Postal Service was supposed to be running it. I've never

been able to find out if Apricot ever shipped any 4.0 to end users.

Despite Gordon Letwin's acid comments about problems with the 80286

processor, I doubt the '286 was the barrier between users and a

multitasking MSDOS. I also doubt there was any shortage of programming

talent at Microsoft - Digital Research's Concurrent DOS and Software

Link's PC-MOS were developed without undue trouble.

MSDOS and PC-DOS have been run on more than just the IBM-PC and clones. Some

of the following have been done:

Hardware PC Emulation:

Apple II -> TransPC 8088 board

Apple MacIntosh -> AST 80286 board

Atari 400/800 -> Co-Power 88 board

Atari ST -> PC-Ditto II cartridge

Commodore Amiga 2000 -> 8088 or A2286D 80286 Bridge Board

IBM PC/RT -> 80286 AT adapter

Kaypro 2 -> Co-Power Plus board

Software PC Emulation:

Apple MacIntosh -> SoftPC

Atari ST -> PC-Ditto I

IBM RS/6000 -> DOS emulation

DOS Emulation:

AIX (IBM RS/6000) -> DOS emulation with "PCSIMulator"

OS/2 -> DOS emulation in "Compatibility Box"

QNX -> DOS window

SunOS -> DOS window

Xenix -> DOS emulation with DOSMerge

WHAT IS DOS?ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**2

DOS exists as a high-level interface between an application program and the

computer. DOS stands for "Disk Operating System", which reflects the fact that

its main original purpose was to provide an interface between the computer and

its disk drives.

DOS now lets your programs do simple memory management, I/O from the system

console, and assorted system tasks (time and date, etc) as well as managing

disk operations. Versions 3.1 and up also incorporate basic networking

functions.

With the introduction of installable device drivers and TSR (terminate but

stay resident) programs in DOS 2.0, the basic DOS functions may be expanded to

cover virtually any scale of operations required.

OTHER OPERATING SYSTEMSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**3

There are a number of compatible replacements for Microsoft's MSDOS. Some are:

Consortium Technologies MultiDOS (multitasking, multiuser)

Digital Research Concurrent DOS (multitasking)

Digital Research Concurrent DOS 386 (for 80386 computers)

Digital Research Concurrent DOS XM (multitasking, multiuser)

Digital Research DR-DOS 3.31 and 4.0 (PC-DOS clones)

PC-MOS/386 (multitasking, multiuser)

Wendin-DOS (multitasking, multiuser)

VM/386 (multitasking)

Various other operating systems are available for the IBM PC. These include:

Digital Research CP/M-86

Digital Research Concurrent CP/M-86 (multitasking)

Minix (multitasking UNIX workalike)

Pick (database-operating system)

QNX (multitasking, multiuser)

UNIX (various systems from IBM itself, Microsoft-SCO, Bell, and various UNIX

clones, single and multi user) (AIX, Xenix, AT&T System V, etc.)

"Shell" programs exist which use DOS only for disk management while they more

or less comprise a new operating system. These include:

DesQview Windows OmniView

GEM TopView TaskView

Systems using the NEC V-series CPUs can execute Intel 8080/8085 8-bit

instructions as well as the 16-bit 8088-up instructions. They can run standard

Digital Research 8-bit CP/M and MP/M directly, as well as other operating

systems developed for that processor.

SPECIFIC VERSIONS OF MS/PC-DOSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**4

DOS 1.x is essentially 86-DOS. DOS 2.x kept the multiple file layout (the two

hidden files and COMMAND.COM) but for all practical purposes is an entirely

different operating system with backwards compatibility with 1.x. I seriously

doubt there has been much code from 1.x retained in 2.x. DOS 3.x is merely an

enhancement of 2.x; there seems little justification for jumping a whole

version number. The disk handling routines were considerably extended in 3.1,

allowing disk access in a "virtual" fashion, independent of whether the drive

was a local or network device. DOS 4.0, originating as it did from outside

Microsoft, can justify a version jump. Unfortunately, 4.x seems to have very

little reason to justify its existence - virtually all of its core features

can be found in one version or another of DOS 3.x. At this time DOS 5 is still

in beta testing. Gordon Letwin of Microsoft says the entire kernel has been

rewritten in hand-optimized assembler and DOS 5 will take advantage of the

'286 and later processors to get extra usable memory.

DOS version nomenclature: major.minor.minor. The digit to the left of the

decimal point indicates a major DOS version change. 1.0 was the first version.

2.0 added support for subdirectories, 3.0 added support for networking, 4.0

added some minimal support for Lotus-Intel-Microsoft EMS.

The first minor version indicates customization for a major application. For

example, 2.1 for the PCjr, 3.3 for the PS/2s. The second minor version does not

seem to have any particular meaning.

The main versions of DOS are:

86-DOS February 1981 Paterson's Quick'n'Dirty DOS first runs on PC

PC-DOS 1.0 August 1981 original IBM release

PC-DOS 1.05 -------- ---- fixes to BASIC interpreter

PC-DOS 1.1 June 1982 bugfix, double sided drive support

MS-DOS 1.25 July 1982 for early compatibles. This is the first non-IBM

OEM version

PC-DOS 2.0 March 1983 for PC/XT, Unix-type subdirectory support,

installable device drivers, I/O redirection,

subdirectories, hard disk support, handle calls

PC-DOS 1.85 April 1983 internal IBM - extended 1.1 - not released

MS-DOS 2.01 -------- 1983 first support for individual country formats, Kanji

PC-DOS 2.1 October 1983 for IBM PCjr, bugfixes for 2.0. No country support

MS-DOS 2.11 October 1983 basically a cross of PC-DOS 2.1 and MS-DOS 2.01

MS-DOS 2.12 -------- ---- special version for TI Professional

PC-DOS 3.0 August 1984 1.2 meg drive for PC/AT, some new system calls,

new external programs, 16-bit FAT, specific support

for IBM network

MS-DOS 3.05 -------- 1984 first OEM version of 3.x

PC-DOS 3.1 November 1984 bugfix for 3.0, implemented generic network support

MS-DOS 2.25 October 1985 extended foreign language support

PC-DOS 3.2 January 1986 720k 3.5 inch drive support, special support for

laptops (IBM PC Convertible), XCOPY

MS-DOS 4.0 April 1986 multitasking (Europe only) - withdrawn from market

PC-DOS 3.3 April 1987 for PS/2 series, 1.44 meg support, multiple DOS

partition support, code page switching, improved

foreign language support, some new function calls,

support for the AT's CMOS clock.

MS-DOS 3.31 November 1987 over-32 meg DOS partitions. Different versions

from different OEMs (not Microsoft). Compaq and

Wyse are most common.

PC-DOS 3.4 -------- ---- internal IBM - not released (4.0 development)

MS-DOS 2.11R -------- 1988 bootable ROM DOS for Tandy machines

PC-DOS 4.0 August 1988 32mb limit officially broken, minor EMS support,

more new function calls, enhanced network support

for external commands

MS-DOS 4.01 January? 1989 Microsoft version with some bugfixes

MS-DOS 3.21R September1989 DOS in ROM, Flash File System for laptops

MS-DOS 3.3R -------- 1990 DOS in ROM, introduced for TI laptops

MS-DOS 5.0 June 1991 new high memory support, uses up to 8 hard disks,

command line editor and aliasing

IBM's PC-DOS was long considered to be the "standard" version of DOS. Now

that MS 5.0 is a commercial product most developers will probably write to it.

Microsoft's policy has been to sell DOS only to OEMs. Despite this, they

sold small quantities of DOS 3.2, 3.3, and 4.0 without insurmountable

difficulties. DOS 5.0 was concieved from the beginning as an over-the-counter

retail product.

Incidentally, IBM refers to its DOS as "The IBM Personal Computer DOS." The

term "PCDOS" is a trademark of IBM's rival DEC.

Some versions of MS-DOS varied from PC-DOS in the available external commands.

Some OEMs only licensed the basic operating system code (the xxxDOS and xxxBIO

programs, and COMMAND.COM) from Microsoft, and either wrote the rest themselves

or contracted them from outside software houses like Phoenix. Most of the

external programs for DOS 3.x and 4.x are written in "C" while the 1.x and 2.x

utilities were written in assembly language. Other OEMs required customized

versions of DOS for their specific hardware configurations, such as Sanyo 55x

and early Tandy computers, which were unable to exchange their DOS with the IBM

version.

PC-DOS 3.0 was extremely buggy on release. It does not handle the DOS

environment correctly and there are numerous documented problems with the

batch file parser. The network support code is also nonfunctional in this DOS

version. It is recommended that users upgrade to at least version 3.1.

DEC MSDOS versions 2.11 for the Rainbow had the ANSI.SYS device driver built

into the main code. The Rainbow also used a unique quad density, single-sided

floppy drive and its DOS had special support for it.

IBM had a version 1.85 of PC-DOS in April 1983, after the introduction of DOS

2.0. It was evidently for internal use only, supported multiple drive file

searches (a primitive form of PATH), builtin MODE sommands for screen support,

a /P parameter for TYPE for paused screens, an editable command stack like the

public domain DOSEDIT.COM utility, and could be set up to remain completely

resident in RAM instead of a resident/transient part like normal DOS. It is a

pity some of the neat enhancements didn't make it into DOS 2.0. IBM also had

an "internal use only" version 3.4, evidently used while developing DOS 4.0.

Digital Research's DR-DOS is the first widely available DOS clone. Version

3.4, released in June 1988, was the one first available to the American public.

It was somewhat buggy and its use is not recommended. DR 3.41 is extremely

compatible and its use should pose no problems on any machine. DR-DOS 5.0

(released May, 1990) is functionally equivalent to MS-DOS 5.0. For all

practical purposes, MS 5.0 is a clone of DR 5.0, since DR beat MS to market by

over a year. According to Greg Ewald, DRI's DR-DOS product manager, DR-DOS was

developed from Concurrent DOS 386 with the multiuser and multitasking code

stripped out.

Some versions of DOS used in compatibles do not maintain the 1.x, 2.x, ...

numbering system. Columbia Data Products computers labeled DOS 1.25 as DOS

2.0. Early Compaqs labeled DOS 2.0 as DOS 1.x. Other versions incorporated

special features - Compaq DOS 3.31 and Wyse DOS 3.21 both support >32mb disk

partitions in the same fashion as DOS 4.x.

AT&T DOS 3.1 differs from generic MSDOS 3.10 in its use of cluster-size and

file allocation table structures. AT&T DOS appears to use rules not from

version 3, but rather those from version 2.

Epson Equity III and ComputerLand 3.10 DOS's appear to use cluster techniques

that are a cross between versions 2 and 3. On type DOS partitions, these DOS's

use 3.x rules if the partition is larger than 32,680 sectors in total size.

This implies 16 bit FAT entries as well. On partitions below this size, they

will use 2.x rules, including the 12 bit FAT entries.

Zenith DOS 3.x and Wyse DOS 3.2 have a builtin internal device driver to

handle up to 4 32Mb DOS partitions on a single hard disk. Wyse DOS 3.31 will

handle single partitions up to 512Mb with a 32-bit FAT.

According to PC Week Magazine, July 4, 1988, Arabic versions of MSDOS are

shipping with a hardware copy-protection system from Rainbow Technologies.

This is similar to the short-lived system used by AutoCAD 2.52 and a very few

other MSDOS programs, where an adapter block is plugged into the parallel port

and software makes use of coded bytes within the block. This type of copy

protection has been common on Commodore products for several years, where it is

called a "dongle."

The AutoCAD dongle was defeated by a small program written within weeks of

version 2.52's debut. Version 2.62 was released 3 months later, without the

dongle. The DOS dongle will, however, prevent the system from booting at all

unless it is found.

This makes the Arabic version of MSDOS the first copy-protected operating

system, a dubious distinction at best. The modifications to the operating

system to support the dongle are not known at this time. Frankly, it would

seem that burning the operating system into ROMs would be cheaper and simpler.

Versions of DOS sold in Great Britain are either newer than those sold in the

US or use a different numbering system. DOS 3.4, 4.0, 4.1, 4.2, and 4.3 had

been released there between the US releases of 3.3 and 4.0.

MSDOS 4.0 (eDOS) was introduced in mid-1987 in Europe (at SICOB in Paris and

sometime earlier by Apricot Computer in the UK). It offered multitasking

provided applications were specially written for it.

David Fraser (Microsoft UK Managing Director) is on record saying that "DOS

4.0 is unlikely to set the world alight and is of interest only to specific

OEMs who want its features for networking and communications." Standard DOS

applications will run under DOS 4.x as a foreground task according to uncertain

information. It differs from earlier versions only in allowing background tasks

to run. For further information, see Chapter 4.

Microsoft changed their OEM licensing agreements between DOS versions 2.x and

3.x. OEM versions of DOS 3.x must maintain certain data areas and undocumented

functions in order to provide compatibility with the networking features of the

operating system. For this reason, resident programs will be much more reliable

when operating under DOS 3.x.

Several versions of DOS have been modified to be run out of ROM. The Sharp

PC5000 had MSDOS 1.25 in ROM, and the Toshiba 1000 and some Tandy 1000 models

have MSDOS 2.11 in ROM. In mid September 1989 Microsoft introduced 3.21R ROMs

for laptops, and in early '90 Texas Instruments laptops were the first to get

the 3.3R ROMs. Digital Research has also announced its DR-DOS 3.41 and 5.0 is

available in a ROM version and Award Software is marketing DOS cards to OEMs

as a plug-in to ISA-bus machines.

IBM's release of DOS 4.0 (and the immediate subsequent release of a bugfix)

was a dubious step "forward." DOS 4.0 was the first version of DOS to come with

a warranty; the catch is that IBM warranted it only for a very slim list of

IBM-packaged software. 4.0 had some minor EMS support, support for large hard

disks, and not much else. With its voracious RAM requirements and lack of

compatibility with previous versions of DOS (many major software packages

crash under DOS 4.0), plus the increase in price to a cool $150, there was

no great rush to go to that version of DOS.

Microsoft undertook development of MSDOS 5.0 in early 1990, soliciting

input from Usenet, BIX, and Compuserve among others. 5.0 is a functional

clone of Digital Research's DR-DOS 5.0. 5.0's compatibility was assured

by what has been claimed as the largest beta-test program in history -

in his address to the Boston Computer Society, Bill Gates announced over

7,500 testers were involved.

THE OPERATING SYSTEM HIERARCHYÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**5

The Disk Operating System (DOS) and the ROM BIOS serve as an insulating layer

between the application program and the machine, and as a source of services

to the application program.

As the term 'system' might imply, DOS is not one program but a collection

of programs designed to work together to allow the user access to programs

and data. Thus, DOS consists of several layers of "control"programs and a set

of "utility" programs.

The system hierarchy may be thought of as a tree, with the lowest level being

the actual hardware. The 8088 or V20 processor sees the computer's address

space as a ladder one byte wide and one million bytes long. Parts of this

ladder are in ROM, parts in RAM, and parts are not assigned. There are also

65,536 "ports" that the processor can use to control devices.

The hardware is normally addressed by the ROM BIOS, which will always know

where everything is in its particular system. The chips may usually also be

written to directly, by telling the processor to write to a specific address or

port. This sometimes does not work as the chips may not always be at the same

addresses or have the same functions from machine to machine.

DOS STRUCTUREÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**6

DOS consists of four components:

* The boot record

* The ROM BIOS interface (IBMBIO.COM, DRBIOS.SYS, or IO.SYS)

* The DOS program file (IBMDOS.COM, DRBDOS.SYS, or MSDOS.SYS)

* The command processor (COMMAND.COM or aftermarket replacement)

* The Boot Record

The boot record begins on track 0, sector 1, side 0 of every diskette formatted

by the DOS FORMAT command. The boot record is placed on diskettes to produce an

error message if you try to start up the system with a nonsystem diskette in

drive A. For hard disks, the boot record resides on the first sector of the DOS

partition. All media supported by DOS use one sector for the boot record.

* Read Only Memory (ROM) BIOS Interface and Extensions

The file IBMBIO.COM or IO.SYS is the interface module to the ROM BIOS.

This file provides a low-level interface to the ROM BIOS device routines and

may contain extensions or changes to the system board ROMs. Some compatibles do

not have a ROM BIOS to extend, and load the entire BIOS from disk. (Sanyo 55x,

Viasyn machines). Some versions of MSDOS, such as those supplied to Tandy, are

named IBMBIO.COM but are not IBM files.

These low-level interface routines include the instructions for performing

operations such as displaying information on the screen, reading the keyboard,

sending data out to the printer, operating the disk drives, and so on. It is

the operating system's means of controlling the hardware. IBMBIO.COM contains

any modifications or updates to the ROM BIOS that are needed to correct any

bugs or add support for other types of hardware such as new disk drives. By

using IBMBIO.COM to update the ROM BIOS on the fly when the user turns on their

computer, IBM does not need to replace the ROM BIOS chip itself, but makes any

corrections through the cheaper and easier method of modifying the IBMBIO.COM

file instead.

IBMBIO.COM also keeps track of hardware operations on an internal stack or

"scratch pad" area for the operating system to save information such as

addresses it will need, etc. An example of the use for this stack can be seen

when running a program such as a word processor. If you have told the word

processor to save your letter, it will write the data to your disk. During this

time, if you start typing some more information, the keyboard generates a

hardware interrupt. Since you don't want the process of writing the information

to the disk to be interrupted, DOS allocates a slot in the stack for the

keyboard's hardware interrupt and when it gets a chance, (probably after the

data has been written to the disk), it can process that interrupt and pick up

the characters you may have been typing. The STACKS= command in DOS 3.2+'s

CONFIG.SYS file controls the number of stack frames availible for this

purpose.

IBMBIO.COM also reads your CONFIG.SYS file and installs any device drivers

(i.e. DEVICE=ANSI.SYS) or configuration commands it may find there.

* The DOS Program

The actual DOS program is the file IBMDOS.COM or MSDOS.SYS. It provides a high-

level interface for user (application) programs. This program consists of file

management routines, data blocking/deblocking for the disk routines, and a

variety of built-in functions easily accessible by user programs.

When a user program calls these function routines, they accept high-level

information by way of register and control block contents. When a user program

calls DOS to perform an operation, these functions translate the requirement

into one or more calls to IBMBIO.COM, MSDOS.SYS or system hardware to complete

the request.

This section is often referred to as the "kernel" by systems programmers.

* The Command Interpreter

The command interpreter, COMMAND.COM, is the part you interact with on the

command line. COMMAND.COM has three parts. IBM calls them the "resident

portion", the "initialization portion" and the "transient portion".

IBM's original documentation spoke of installing alternate command

interpreters (programs other than COMMAND.COM) with the SHELL= statement in

CONFIG.SYS. Unfortunately, IBM chose not to document much of the interaction

between IBMDOS.COM and IBMBIO.COM. By the time much of the interaction was

widely understood, many commercial software programs had been written to use

peculiarities of COMMAND.COM itself.

Two programs exist that perform as actual "shells" by completely replacing

COMMAND.COM and substituting their own command interpreter to use with the

hidden DOS files. These are Command Plus, a commercial package, and the very

interesting shareware 4DOS package. Both supply greatly enhanced batch

language and editing capabilities.

NOTE: DOS 3.3+ checks for the presence of a hard disk, and will default to

COMSPEC=C:\. Previous versions default to COMSPEC=A:\. Under some DOS

versions, if COMMAND.COM is not immediately availible for reloading

(i.e., swapping to a floppy with COMMAND.COM on it) DOS may crash.

Resident Portion:

The resident portion resides in memory immediately following IBMDOS.COM and its

data area. This portion contains routines to process interrupts 22h (Terminate

Address), 23h (Ctrl-Break Handler), and 24h (Critical Error Handler), as well as

a routine to reload the transient portion if needed. For DOS 3.x, this portion

also contains a routine to load and execute external commands, such as files

with exensions of COM or EXE.

When a program terminates, a checksum is used to determine if the application

program overlaid the transient portion of COMMAND.COM. If so, the resident

portion will reload the transient portion from the area designated by COMSPEC=

in the DOS environment. If COMMAND.COM cannot be found, the system will halt.

All standard DOS error handling is done within the resident portion of

COMMAND.COM. This includes displaying error messages and interpreting the

replies to the "Abort, Retry, Ignore, Fail?" message.

Since the transient portion of COMMAND.COM is so large (containing the

internal commands and all those error messages), and it is not needed when the

user is running an application it can be overlaid that program if that

application needs the room. When the application is through, the resident

portion of COMMAND.COM brings the transient portion back into memory to show

the prompt. This is why you will sometimes see the message "Insert disk with

COMMAND.COM". It needs to get the transient portion off the disk since it was

overlaid with the application program.

The initialization portion of COMMAND.COM follows the resident portion and is

given control during the bootup procedure. This section actually processes the

AUTOEXEC.BAT file. It also decides where to load the user's programs when they

are executed. Since this code is only needed during startup, it is overlaid by

the first program which COMMAND.COM loads.

The transient portion is loaded at the high end of memory and it is the

command processor itself. It interprets whatever the user types in at the

keyboard, hence messages such as "Bad command or file name" for when the user

misspells a command. This portion contains all the internal commands (i.e.

COPY, DIR, RENAME, ERASE), the batch file processor (to run .BAT files) and

a routine to load and execute external commands which are either .COM or

.EXE files.

The transient portion of COMMAND.COM produces the system prompt, (C>), and

reads what the user types in from the keyboard and tries to do something with

it. For any .COM or .EXE files, it builds a command line and issues an EXEC

function call to load the program and transfer control to it.

DOS INITIALIZATIONÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1**7

The system is initialized by a software reset (Ctrl-Alt-Del), a hardware reset

(reset button), or by turning the computer on. The Intel 80x8x series processors

always look for their first instruction at the end of their address space

(0FFFF0h) when powered up or reset. This address contains a jump to the first

instruction for the ROM BIOS.

Built-in ROM programs (Power-On Self-Test, or POST, in the IBM) check machine

status and run inspection programs of various sorts. Some machines set up a

reserved RAM area with bytes indicating installed equipment (AT and PCjr).

When the ROM BIOS finds a ROM on an adapter card, it lets that ROM take

control of the system so that it may perform any set up necessary to use the

hardware or software controlled by that ROM. The ROM BIOS searches absolute

addresses C8000h through E0000h in 2K increments in search of a valid ROM.

A valid ROM is determined by the first few bytes in the ROM. The ROM will have

the bytes 55h, AAh, a length indicator and then the assembly language

instruction to CALL FAR (to bring in a "FAR" routine). A checksum is done on

the ROM to verify its integrity, then the BIOS performs the CALL FAR to bring

in the executible code. The adapter's ROM then performs its initialization

tasks and hopefully returns control of the computer back to the ROM BIOS so it

can continue with the booting process.

The ROM BIOS routines then look for a disk drive at A: or an option ROM

(usually a hard disk) at absolute address C:800h. If no floppy drive or option

ROM is found, the BIOS calls int 19h (ROM BASIC if it is an IBM) or displays

an error message.

If a bootable disk is found, the ROM BIOS loads the first sector of information

from the disk and then jumps into the RAM location holding that code. This code

normally is a routine to load the rest of the code off the disk, or to "boot"

the system.

The following actions occur after a system initialization:

1. The boot record is read into memory and given control.

2. The boot record then checks the root directory to assure that the first

two files are IBMBIO.COM and IBMDOS.COM. These two files must be the

first two files, and they must be in that order (IBMBIO.COM first, with

its sectors in contiguous order).

NOTE: IBMDOS.COM need not be contiguous in version 3.x+.

3. The boot record loads IBMBIO.COM into memory.

4. The initialization code in IBMBIO.COM loads IBMDOS.COM, determines

equipment status, resets the disk system, initializes the attached

devices, sets the system parameters and loads any installable device

drivers according to the CONFIG.SYS file in the root directory (if

present), sets the low-numbered interrupt vectors, relocates IBMDOS.COM

downward, and calls the first byte of DOS.

NOTE: CONFIG.SYS may be a hidden file.

5. DOS initializes its internal working tables, initializes the interrupt

vectors for interrupts 20h through 27h, and builds a Program Segment

Prefix for COMMAND.COM at the lowest available segment. For DOS versions

3.10 up, DOS also initializes the vectors for interrupts 0Fh through 3Fh.

An initialization routine is included in the resident portion and assumes

control during startup. This routine contains the AUTOEXEC.BAT file

handler and determines the segment address where user application programs

may be loaded. The initialization routine is then no longer needed and is

overlaid by the first program COMMAND.COM loads.

NOTE: AUTOEXEC.BAT may be a hidden file.

6. IBMDOS.COM uses the EXEC function call to load and start the top-level

command processor. The default command processor is COMMAND.COM in the

root directory of the boot drive. If COMMAND.COM is in a subdirectory

or another command processor is to be used, it must be specified by a

SHELL= statement in the CONFIG.SYS file.

A transient portion is loaded at the high end of memory. This is the

command processor itself, containing all of the internal command

processors and the batch file processor. For DOS 2.x, this portion also

contains a routine to load and execute external commands, such as files

with extensions of COM or EXE.

This portion of COMMAND.COM also produces the DOS prompt (such as "A>"),

reads the command from the standard input device (usually the keyboard or

a batch file), and executes the command. For external commands, it builds

a command line and issues an EXEC function call to load and transfer

control to the program.

note 1) COMMAND.COM may be a hidden file.

2) For IBM DOS 2.x, the transient portion of the command processor

contains the EXEC routine that loads and executes external commands.

For MSDOS 2.x+ and IBM DOS 3.x+, the resident portion of the command

processor contains the EXEC routine.

3) IBMDOS only checks for a file named "COMMAND.COM". It will load

any file of that name if no SHELL= command is used.

That pretty much covers the bootup process. After the command processor is

loaded, it runs the AUTOEXEC.BAT file and then the user gets their prompt to

begin working.

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

C H A P T E R T W O

CPU Port Assignments, System Memory Map, BIOS Data Area, Interrupts 00h to 09h

C O N T E N T S

Introduction .......................................................... 2**1

System Memory Map ..................................................... 2**2

A Brief Guide to Current Memory Terminology ........................... 2**3

PC Port Assignment .................................................... 2**4

Reserved Memory Locations ............................................. 2**5

Absolute Addresses .................................................... 2**6

The IBM PC System Interrupts (Overview) ............................... 2**7

Quick Chart of Interrupts 00h-0FFh .................................... 2**8

The IBM-PC System Interrupts 00h-0Fh (in detail) ...................... 2**9

Introduction .......................................................... 2**1

For consistency in this reference, all locations and offsets are in

hexadecimal unless otherwise specified. All hex numbers are prefaced with a

leading zero if they begin with an alphabetic character, and are terminated

with a lowercase H (h). The formats vary according to common usage.

System Memory Map ..................................................... 2**2

The IBM PC handles its address space in 64k segments, divided into 16k

fractions and then further as necessary.

ÚÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³start ³start³end ³ ³

³addr. ³addr.³addr.³ usage ³

³(dec) ³ (hex) ³ ³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ *640k RAM Area* ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0k ³ ³ start of RAM, first K is interrupt vector table ³

³ 16k ³00000-03FFF³ PC-0 system board RAM ends ³

³ 32k ³04000-07FFF³ ³

³ 48k ³08000-0BFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 64k ³10000-13FFF³ PC-1 system board RAM ends ³

³ 80k ³14000-17FFF³ ³

³ 96k ³18000-1BFFF³ ³

³ 112k ³1C000-1FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 128k ³20000-23FFF³ ³

³ 144k ³24000-27FFF³ ³

³ 160k ³28000-2BFFF³ ³

³ 176k ³2C000-2FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 192k ³30000-33FFF³ ³

³ 208k ³34000-37FFF³ ³

³ 224k ³38000-3BFFF³ ³

³ 240k ³3C000-3FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 256k ³40000-43FFF³ PC-2 system board RAM ends ³

³ 272k ³44000-47FFF³ ³

³ 288k ³48000-4BFFF³ ³

³ 304k ³4C000-4FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 320k ³50000-53FFF³ ³

³ 336k ³54000-57FFF³ ³

³ 352k ³58000-5BFFF³ ³

³ 368k ³5C000-5FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 384k ³60000-63FFF³ ³

³ 400k ³64000-67FFF³ ³

³ 416k ³68000-6BFFF³ ³

³ 432k ³6C000-6FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 448k ³70000-73FFF³ ³

³ 464k ³74000-77FFF³ ³

³ 480k ³78000-7BFFF³ ³

³ 496k ³7C000-7FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 512k ³80000-83FFF³ ³

³ 528k ³84000-87FFF³ ³

³ 544k ³88000-8BFFF³ the original IBM PC-1 BIOS limited memory to 544k ³

³ 560k ³8C000-8FFFF³ ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 576k ³90000-93FFF³ ³

³ 592k ³94000-97FFF³ ³

³ 609k ³98000-9BFFF³ ³

³ 624k ³9C000-9FFFF³ to 640k (top of RAM address space) ³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³A0000 ***** 64k ***** EGA/VGA starting address ³

³A0000 ***** 64k ***** Toshiba 1000 DOS ROM (MS-DOS 2.11V) ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 640k ³A0000-A95B0³ MCGA 320x200 256 color video buffer ³

³ ³ -AF8C0³ MCGA 640x480 2 color video buffer ³

³ ³ -A3FFF³ ³

³ 656k ³A4000-A7FFF³ ³

³ 672k ³A8000-ABFFF³ this 64k segment may be used for contiguous DOS ³

³ 688k ³AC000-AFFFF³ RAM with appropriate hardware and software ³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³B0000 ***** 64k ***** mono and CGA address ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 704k ³B0000-B3FFF³ 4k monochrome display | The PCjr and early Tandy 1000³

³ 720k ³B4000-B7FFF³ | BIOS revector direct write to³

³ 736k ³B8000-BBFFF³ 16k CGA uses | the B8 area to the Video Gate³

³ 756k ³BC000-BFFFF³ | Array and reserved system RAM³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³C0000 ***** 64k *************** expansion ROM ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 768k ³C0000-C3FFF³ 16k EGA BIOS C000:001E EGA BIOS signature (letters IBM ³

³ 784k ³C4000-C5FFF³ ³

³ ³C6000-C63FF³ 256 bytes Professional Graphics Display comm. area ³

³ ³C6400-C7FFF³ ³

³ 800k ³C8000-CBFFF³ 16k hard disk controller BIOS, drive 0 default ³

³ ³CA000 ³ some 2nd floppy (high density) controller BIOS ³

³ 816k ³CC000-CDFFF³ 8k IBM PC Network NETBIOS ³

³ ³CE000-CFFFF³ ³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³D0000 ***** 64k ***** expansion ROM ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 832k ³D0000-D7FFF³ 32k IBM Cluster Adapter | PCjr first ROM cartridge ³

³ ³ DA000³ voice communications | address area. ³

³ 848k ³D4000-D7FFF³ | Common expanded memory board ³

³ 864k ³D8000-DBFFF³ | paging area. ³

³ 880k ³DC000-DFFFF³ | ³

³ ³DE000 ³ TI Pro default video buffer, 4k in length ³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³E0000 ***** 64k ***** expansion ROM ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 896k ³E0000-E3FFF³ | PCjr second ROM cartridge ³

³ 912k ³E4000-E7FFF³ | address area ³

³ 928k ³E8000-EBFFF³ | ³

³ 944k ³EC000-EFFFF³ | spare ROM sockets on AT ³

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³F0000 ***** 64k ***** system ³

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 960k ³F0000-F3FFF³ reserved by IBM | cartridge address ³

³ 976k ³F4000- ³ | area (PCjr cartridge ³

³ ³F6000 ³ ROM BASIC Begins | BASIC) ³

³ 992k ³F8000-FB000³ | ³

³ 1008k³FC000-FFFFF³ ROM BASIC and original | ³

³ ³ ³ BIOS (Compatibility BIOS | ³

³ ³ ³ in PS/2) | ³

³ 1024k³ FFFFF³ end of memory (1024k) for 8088 machines ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÁÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 384k ³100000-15FFFF³ 80286/AT extended memory area, 1Mb motherboard ³

³ 15Mb ³100000-FFFFFF³ 80286/AT extended memory address space ³

³ 15Mb ³160000-FDFFFF³ Micro Channel RAM expansion (15Mb extended memory) ³

³ 128k ³FE0000-FFFFFF³ system board ROM (PS/2 Advanced BIOS) ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 64k ³C0000000-C000FFFF³ Weitek "Abacus" math coprocessor memory-mapped I/O ³

ÀÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

Note that the ROM BIOS has a duplicated address space which causes it to

"appear" both at the end of the 1 megabyte real mode space and at the end of

the 16 megabyte protected mode space. The addresses from 0E0000 to 0FFFFF are

equal to 0FE0000 to 0FFFFFF. This is necessary due to differences in the memory

addressing between Real and Protected Modes.

A Brief Guide to Current Memory Terminology ........................... 2**3

LOW MEMORY - 0000h to around 0:5(something), comprising the 80x8x interrupt

vector table, the BIOS Data Area, DOS Data Area, etc.

CONVENTIONAL MEMORY - from the end of low memory to the beginning of the

"reserved by IBM" A000 segment (640k).

HIGH MEMORY - originally noncontiguous RAM stuffed into the "reserved for

ROM expansion" areas, typically segments D000 and E000. DOS

normally can't access this memory without a driver of some

sort, but it's easy to put RAMdisks and stuff in there.

CONVENTIONAL MEMORY - extra RAM stuck at A000, assuming the machine already

has 640k, appears as conventional memory accessible to DOS

and applications. IBM clones can typically add 64k before

bumping into a mono card or 96k before hitting a color card.

This address is part of the EGA/VGA video RAM area and most

EGA cards don't like system memory at A000.

EXPANDED MEMORY - LIM 3.2, LIM 4.0, or EEMS 3.2 bank switched memory. A

RAM "window" allows an app to save a block of RAM to an expansion

board. The window size and location varies according to the

EMS standard being used.

EXTENDED MEMORY - this is the "native mode" address space of the 80286 and

later chips. The "real mode", or 8088 addressing scheme,

sees RAM as a collection of segments and offsets with a limit

on segment size. "Protected mode" addressing uses a flat linear

addressing scheme. 8088 and 80188 chips do not have extended

memory.

HIGH MEMORY - by fiddling a bit with the segment/offset stuff, you can

get an extra block of addressable 8088-mode memory just over

the 1 meg address space. Microsoft issued their "HMA" (High

Memory Area) standard to try to standardize use of this block.

Though it really is "high" memory, "high" had for many years

referred to memory between 640k and 1mb. This creates more

confusion for new programmers.

EMS - this is expanded memory as described above

XMS - Microsoft is pushing an "Extended Memory Standard" which defines

a page-switching scheme much like EMS. The only real difference is

that XMS uses protected-mode RAM instead of a special paged RAM board.

XMS - some severely brain-damaged jerk at IBM issued documentation for some

IBM *EMS* boards referring to the boards as *XMS*. This was a classic

blunder, and now some IBM-followers are picking up the aberrant

terminology. This is guaranteed to confuse some people. To make it

simple, if it needs an expansion board, it is EMS no matter what the

vendor calls it.

PC Port Assignment .................................................... 2**4

These are functions common across the IBM range. The PCjr, PC-AT, PC

Convertible and PS/2 (both buses) have enhancements. In some cases, the

AT and PS/2 series ignore, duplicate, or reassign ports arbitrarily. If

your code incorporates specific port addresses for video or system board

control it would be wise to have your application determine the machine

type and video adapter and address the ports as required.

hex address Function Models

PCjr|PC|XT|AT|CVT|M30|PS2

0000-000F 8237 DMA controller PC

0010-001F 8237 DMA controller AT PS2

0020-0027 8259A interrupt controller

0020-002F IOSGA interrupt function PS2

0020-003F 8259A interrupt controller (AT)

0020-0021 interrupt controller 1, 8259A PC AT PS2

0040-0043 programmable timer 8253 PC

0040-0047 programmable timers PS2

0040-005F 8253-5 programmable timers AT

note 1) 0041 was memory refresh in PCs. Not used in PS/2.

2) A few early 80386 machines used static RAM and did

not use refresh at all. The PCjr refreshes by the

video vertical retrace signal.

0060-0063 keyboard controller 8255A PC

0060-006F 8042 keyboard controller AT

0060 IOSGA keyboard input port PS2

0061 speaker PCjr PC XT AT CVT

0061 IOSGA speaker control M30 PS2

0061 On some clones, setting or clearing bit 2 controls Turbo mode

0061 Toshiba 1000 - system command

0062 IOSGA configuration control M30 PS2

0062 Toshiba 1000 - System Status, port C

0063 SSGA, undocumented PS2

0063 Toshiba 1000 - mode set

0064 keyboard auxiliary device PS2

0065-006A SSGA, undocumented PS2

006B SSGA, RAM enable/remap PS2

006C-006F SSGA, undocumented PS2

0070 AT CMOS write internal register

0071 AT CMOS read internal register

0070-0071 CMOS real-time clock, NMI mask PS2

0070-007F CMOS real-time clock, NMI mask AT

0074-0076 reserved PS2

0800-008F SSGA DMA page registers PS2

0080-009F DMA page registers, 74LS612 AT

0090 central arbitration control port (Micro Channel)

0091 card selected feedback (Micro Channel)

0092 system control port A (Micro Channel)

0093 reserved (Micro Channel)

0094 system board setup (Micro Channel)

0096 POS "CD SETUP" selector (Micro Channel)

00A0-00A1 Interrupt controller 2, 8259A AT PS2

00A0-00AF IOSGA NMI mask register PS2

00B0-00BF realtime clock/calendar, (undocumented) PS2

00C0-00DF reserved PCjr PC XT AT CVT M30

00C0-00CF DOS ROM register, Toshiba 1000

00D0-00EF "special" register, Toshiba 1000

00C0 0C1 key register, Toshiba 1000

00C1 keyboard transfer register, Toshiba 1000

00C2 keyboard receive register, Toshiba 1000

00C3 keyboard status register, Toshiba 1000

00C8 DOS ROM page register, Toshiba 1000

00E0 CPU speed control, Toshiba 1000

00E1 keyboard status/0E2 key register, Toshiba 1000

00E2 work register, Toshiba 1000

00E3 0E4 key register, Toshiba 1000

00E4 system control register 0, Toshiba 1000

00E4 Weitek ABACUS NDP - bit 0=1, ABACUS is present

00E5 0E6 key register, Toshiba 1000

00E6 system control register 1, Toshiba 1000

00EE EMS unit index, Toshiba 1000

00EF EMS unit data, Toshiba 1000

00C0-00DF DMA controller 2, 8237A-5 AT PS2

00E0-00EF realtime clock/calendar (undocumented) M30 PS2

00F0-00FF PS/2 math coprocessor I/O (Model 50+) (diskette IO on PCjr)

0100-0101 PS/2 POS adapter ID response (Micro Channel)

0102-0107 PS/2 POS adapter configuration response (Micro Channel)

01F0-01F8 hard disk AT PS2

0200-0201 game-control adapter (joystick)

0200-020F game controller PC AT

0208-0209 Chips & Technology CS8221 chipset default EMS ports

alternate addresses: 218h, 258h, 268h, 2A8h, 2B8h, 2E8h

0208-020F Toshiba 1000 - EMS unit I/O #1

020C-020D reserved by IBM

0210-0217 expansion box (PC, XT)

0218-021F Toshiba 1000 - EMS unit I/O #2

021F reserved by IBM

0258-025F Toshiba 1000 - EMS unit I/O #3

0258-0259 LIM EMS 3.1 (not defined in 3.2+)

0268-026F Toshiba 1000 - EMS unit I/O #4

0278-027F parallel printer port 2 AT

0278-027B parallel printer port 3 PS2

02A2 clock chip in early Sperry PCs

02A8-02AF Toshiba 1000 - EMS unit I/O #5

02B8-02BF Toshiba 1000 - EMS unit I/O #6

02B0-02DF EGA (alternate) PC AT

02C0-02DF Toshiba 1000 - realtime clock

02E1 GPIB (adapter 0) AT

02E2-02E3 data acquisition (adapter 0) AT

02E8 "industry standard" COM4

02E8-02EF Toshiba 1000 - EMS unit I/O #7

02F8-02FF serial communications (COM2) PC AT PS2

0300-031F prototype card PC AT

0300-031F Leading Edge Model D clock -------------------

0320-032F hard disk controller PC

0320 Perstor HD controller, primary -------------------

0324 Perstor HD controller, secondary -------------------

0340 Sony CD-ROM -------------------

0348-0357 DCA 3278

0360-0367 PC Network (low address)

0368-036F PC Network (high address) AT

0370 Colorado Memory external tape backup control port -------

some "second controller" floppy cards -------------------

0378-037F parallel printer port PC AT

0378-037B parallel printer port PS2

0380-038F Eicon Technology Network Adapter (X.25) board (default)

0380-038F SDLC, bi-synchronous 2 PC AT

0380-0389 BSC communications (alternate) PC

0390-039F Eicon Technology Network Adapter (X.25) board (alternate)

0390-0393 cluster (adapter 0) PC AT

03A0-03A9 BSC communications (primary) PC AT

03B0-03BF monochrome/parallel printer adapter PC AT

03B4-03B5 video subsystem PS2

03BA video subsystem PS2

03BC-03BF parallel printer port 1 PS2

03C0-03CF Enhanced Graphics Adapter

03C0-03DA video subsystem and DAC PS2

03DA video status register AT&T 6300, Olivetti PC

03D0-03DF CGA, MCGA, VGA adapter control

03DE video mode selector register AT&T 6300, Olivetti PC

03E8h "industry standard" COM3

03F0-03F7 floppy disk controller PC AT PS2

03F0 Colorado Memory internal tape backup control port -------

03F2 DTK high-density XT floppy controller (output only)

03F5 DTK high-density XT floppy controller

03F8-03FF serial communications (COM1) PC AT PS2

06E2-06E3 data acquisition (adapter 1) AT

0790-0793 cluster (adapter 1) PC AT

0878 Compaq 386SX VGA BIOS relocation AT

0AE2-0AE3 data acquisition (adapter 2) AT

0B90-0B93 cluster (adapter 2) PC AT

0EE2-0EE3 data acquisition (adapter 3) AT

1390-1393 cluster (adapter 3) PC AT

22E1 GPIB (adapter 1)

2390-2393 cluster (adapter 4) PC AT

4258 LIM EMS 3.1 (not defined in 3.2+) -------------------

42E1 GPIB (adapter 2) AT

62E1 GPIB (adapter 3) AT

8258 LIM EMS 3.1 (not defined in 3.2+) -------------------

82E1 GPIB (adapter 4) AT

A2E1 GPIB (adapter 5) AT

C258 LIM EMS 3.1 (not defined in 3.2+) -------------------

C2E1 GPIB (adapter 6) AT

E2E1 GPIB (adapter 7) AT

note 1) IOSGA = I/O Support Gate Array

SSGA = System Support Gate Array

2) I/O Addresses, hex 000 to 0FF, are reserved for the system board I/O.

Hex 100 to 3FF are available on the I/O channel.

3) These are the addresses decoded by the current set of adapter cards.

IBM may use any of the unlisted addresses for future use.

4) SDLC Communication and Secondary Binary Synchronous Communications

cannot be used together because their port addresses overlap.

Reserved Memory Locations ............................................. 2**5

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 000-3FF - 1k DOS interrupt vector table, 4 byte vectors for ints 00h-0FFh.

³ 30:00 - used as a stack area during POST and bootstrap routines. This

³to 3F:FF stack area may be revectored by an application program.

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ ** The BIOS Data Area ** addresses from 400h to 4FFh

ÃÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³addr.³ size ³ description

ÃÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³40:00³ word ³ COM1 port address | These addresses are zeroed out in the

³40:02³ word ³ COM2 port address | OS/2 DOS Compatibility Box if any of

³40:04³ word ³ COM3 port address | the OS/2 COMxx.SYS drivers are loaded.

³40:06³ word ³ COM4 port address |

³40:08³ word ³ LPT1 port address

³40:0A³ word ³ LPT2 port address

³40:0C³ word ³ LPT3 port address

³40:0E³ word ³ LPT4 port address (not valid in PS/2 machines)

³40:0E³ word ³ PS/2 pointer to 1k extended BIOS Data Area at top of RAM

³40:10³ word ³ equipment flag (see int 11h)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bits:

³ 0 0 no floppy drive present

³ 1 if floppy drive present (see bits 6&7)

³ 1 0 no math coprocessor installed

³ 1 if 80x87 installed (not valid in PCjr)

³ 2,3 system board RAM (not used on AT or PS/2)

³ 0,0 16k 0,1 32k

³ 1,0 48k 1,1 64k

³ 4,5 initial video mode

³ 0,0 no video adapter

³ 0,1 40 column color (PCjr default)

³ 1,0 80 column color

³ 1,1 MDA

³ 6,7 number of diskette drives

³ 0,0 1 drive 0,1 2 drives

³ 1,0 3 drives 1,1 4 drives

³ 8 0 DMA present

³ 1 DMA not present (PCjr, Tandy 1400, Sanyo 55x)

³ 9,A,B number of RS232 serial ports

³ C game adapter (joystick)

³ 0 no game adapter

³ 1 if game adapter

³ D serial printer (PCjr only)

³ 0 no printer

³ 1 serial printer present

ÚÄÄÄÄÄÄÙ E,F number of parallel printers installed

³note 1) The IBM PC and AT store the settings of the system board

ÀÄÄÄ¿ switches or CMOS RAM setup information (as obtained by the BIOS

³ in the Power-On Self Test (POST)) at addresses 40:10h and

³ 40:13h. 00000001b indicates "on", 00000000b is "off".

ÚÄÄÄÄÄÂÄÄÄÄÁÄÄ¿

³40:12³ byte ³ reserved (PC, AT)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ number of errors detected by infrared keyboard link (PCjr)

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ POST status (Convertible)

³40:13³ word ³ availible memory size in Kbytes (less display RAM in PCjr)

ÃÄÄÄÄÄÅÄÄÄÄÄÄÄ´ this is the value returned by int 12h

³40:15³ word ³ reserved

³40:17³ byte ³ keyboard flag byte 0 (see int 9h)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7 insert mode on 3 alt pressed

³ 6 capslock on 2 ctrl pressed

³ 5 numlock on 1 left shift pressed

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 4 scrollock on 0 right shift pressed

³40:18³ byte ³ keyboard flag byte 1 (see int 9h)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7 insert pressed 3 ctrl-numlock (pause) toggled

³ 6 capslock pressed 2 PCjr keyboard click active

³ 5 numlock pressed 1 PCjr ctrl-alt-capslock held

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 4 scrollock pressed 0

³40:19³ byte ³ storage for alternate keypad entry (not normally used)

³40:1A³ word ³ pointer to keyboard buffer head character

³40:1C³ word ³ pointer to keyboard buffer tail character

³40:1E³32bytes³ 16 2-byte entries for keyboard circular buffer, read by int 16h

³40:3E³ byte ³ drive seek status - if bit=0, next seek will recalibrate by

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ repositioning to Track 0.

³ bit 3 drive D bit 2 drive C

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 1 drive B 0 drive A

³40:3F³ byte ³ diskette motor status (bit set to indicate condition)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7 write in progress 3 motor on (floppy 3)

³ 6 2 motor on (floppy 2)

³ 5 1 B: motor on (floppy 1)

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 4 0 A: motor on (floppy 0)

³40:40³ byte ³ motor off counter

³ ³ ³ starts at 37 and is decremented 1 by each system clock tick.

³ ³ ³ motor is shut off when count = 0.

³40:41³ byte ³ status of last diskette operation where:

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7 timeout failure 3 DMA overrun

³ 6 seek failure 2 sector not found

³ 5 controller failure 1 address not found

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 4 CRC failure 0 bad command

³40:42³7 bytes³ NEC floppy controller chip status

³40:49³ byte ³ Video Control Data Area 1 from 0040:0049 through 0040:0066

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ current CRT mode (hex value)

³ 00h 40x25 BW (CGA) 01h 40x25 color (CGA)

³ 02h 80x25 BW (CGA) 03h 80x25 color (CGA)

³ 04h 320x200 color (CGA) 05h 320x200 BW (CGA)

³ 06h 640x200 BW (CGA) 07h monochrome (MDA)

³extended video modes (EGA/MCGA/VGA or other)

³ 08h lores,16 color 09h med res,16 color

³ 0Ah hires,4 color 0Bh n/a

³ 0Ch med res,16 color 0Dh hires,16 color

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 0Eh hires,4 color 0Fh hires,64 color

³40:4A³ word ³ number of columns on screen, coded as hex number of columns

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ 20 col = 14h (video mode 8, low res 160x200 CGA graphics)

³ 40 col = 28h

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 80 col = 46h

³40:4C³ word ³ screen buffer length in bytes

ÃÄÄÄÄÄÅÄÄÄÄÄÄÄ´(number of bytes used per screen page, varies with video mode)

³40:4E³ word ³ current screen buffer starting offset (active page)

³40:50³8 words³ cursor position pages 1-8

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ the first byte of each word gives the column (0-19, 39, or 79)

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ the second byte gives the row (0-24)

³40:60³ byte ³ end line for cursor (normally 1)

³40:61³ byte ³ start line for cursor (normally 0)

³40:62³ byte ³ current video page being displayed (0-7)

³40:63³ word ³ base port address of 6845 CRT controller or equivalent

ÃÄÄÄÄÄÅÄÄÄÄÄÄÄ´ for active display 3B4h=mono, 3D4h=color

³40:65³ byte ³ current setting of the CRT mode register

³40:66³ byte ³ current palette mask setting (CGA)

³40:67³5 bytes³ temporary storage for SS:SP during shutdown (cassette interface)

³40:6C³ word ³ timer counter low word

³40:6E³ word ³ timer counter high word

³40:69³ byte ³ HD_INSTALL (Columbia PCs) (not valid on most clone computers)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 0 0 8 inch external floppy drives

³ 1 5-1/4 external floppy drives

³ 1,2 highest drive address which int 13 will accept

³ (since the floppy drives are assigned 0-3,subtract

³ 3 to obtain the number of hard disks installed)

³ 4,5 # of hard disks connected to expansion controller

³ 6,7 # of hard disks on motherboard controller

³ (if bit 6 or 7 = 1, no A: floppy is present and

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ the maximum number of floppies from int 11 is 3)

³40:70³ byte ³ 24 hour timer overflow 1 if timer went past midnight

ÃÄÄÄÄÄÅÄÄÄÄÄÄÄ´ it is reset to 0 each time it is read by int 1Ah

³40:71³ byte ³ BIOS break flag (bit 7 = 1 means break key hit)

³40:72³ word ³ reset flag

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ PCjr keeps 1234h here for softboot when a cartridge is installed

³ bits 1234h = soft reset, memory check will be bypassed

³ 4321h = preserve memory (PS/2 only)

³ 5678h = system suspended (Convertible)

³ 9ABCh = manufacturing test mode (Convertible)

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ ABCDh = system POST loop mode (Convertible)

³40:74³ byte ³ status of last hard disk operation ; PCjr special disk control

³40:75³ byte ³ # of hard disks attached (0-2) ; PCjr special disk control

³40:76³ byte ³ HD control byte; temp holding area for 6th param table entry

³40:77³ byte ³ port offset to current hd adapter ; PCjr special disk control

³40:78³4 bytes³ timeout value for LPT1,LPT2,LPT3,LPT4

³40:7C³4 bytes³ timeout value for COM1,COM2,COM3,COM4 (0-0FFh secs, default 1)

³40:80³ word ³ pointer to start of circular keyboard buffer, default 03:1E

³40:82³ word ³ pointer to end of circular keyboard buffer, default 03:3E

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ note: early Zenith Z183 BIOS set these pointers to zero and

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ ignored them.

³40:84³ .... ³ Video Control Data Area 2, 0040:0084 through 0040:008A

³40:84³ byte ³ rows on the screen minus 1 (EGA only)

³40:84³ byte ³ PCjr interrupt flag; timer channel 0 (used by POST)

³40:85³ word ³ bytes per character (EGA only)

³40:85³2 bytes³ (PCjr only) typamatic character to repeat

³40:86³2 bytes³ (PCjr only) typamatic initial delay

³40:87³ byte ³ mode options (EGA only)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 0 0 cursor emulation in effect

³ 1 no cursor emulation

³ 1 0 EGA is connected to a color display

³ 1 EGA is connected to monochrome TTL display

³ 2 0 wait for vertical retrace (CGA active)

³ 1 don't wait for vertical retrace (EGA or MDA active)

³ 3 0 EGA is the active display,

³ 1 "other" display is active.

³ 4 reserved

³ 5,6 EGA memory size

³ 0,0 64k

³ 0,1 128k

³ 1,0 192k

³ 1,1 256k

³ 7 0 don't clear screen on mode changes

³ 1 if the last "set mode" specified not to clear the

³ video buffer

³ mode combinations:

³ bit3 bit1 Meaning

³ 0 0 EGA is active display and is color

³ 0 1 EGA is active display and is monochrome

³ 1 0 EGA is not active, a mono card is active

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 1 1 EGA is not active, a CGA is active

³40:87³ byte ³ (PCjr only) current Fn key code

ÃÄÄÄÄÄÅÄÄÄÄÄÄÄ´ 80h bit indicates make/break key code?

³40:88³ byte ³ feature bits and switches (EGA only) 0=on, 1=off

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 0 switch 1

³ 1 switch 2

³ 2 switch 3

³ 3 switch 4

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 4-7 feature bits

³40:88³ byte ³ (PCjr only) special keyboard status byte

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7 function flag 3 typamatic (0=enable,1=disable)

³ 6 Fn-B break 2 typamatic speed (0=slow,1=fast)

³ 5 Fn pressed 1 extra delay bef.typamatic (0=enable)

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 4 Fn lock 0 write char, typamatic delay elapsed

³40:89³ byte ³ (PCjr) current value of 6845 reg 2 (horizontal synch) used by

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ ctrl-alt-cursor screen positioning routine in ROM

³ (VGA)

³ bit 0 reserved

³ 1 video summing enabled

³ 2 0 for color monitor attached

³ 1 for mono monitor

³ 3 0 for default palette loading enabled

³ 4 0 for 8x8 text font

³ 1 for 8x16 text font

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 5-7 reserved

³40:8A³ byte ³ (PCjr) CRT/CPU Page Register Image, default 3Fh

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ (VGA) Display Combination Code Index. This is the value

³ set/returned by function 1Ah of the Video BIOS. This byte

³ contains an index into the ROM BIOS Display Combination Code

³ table, which is a list of byte pairs that specify valid

³ combinations of one or two video subsystems. Video subsystems

³ are designated by the following values:

³ 00h no display

³ 01h MDA with monochrome display

³ 02h CGA with color display

³ 03h reserved

³ 04h EGA with color display

³ 05h EGA with monochrome display

³ 06h Professional Graphics Adapter

³ 07h VGA with analog monochrome display

³ 08h VGA with analog color display

³ 09h reserved

³ 0Ah MCGA with digital color display

³ 0Bh MCGA with analog monochrome display

³ 0Ch MCGA with analog color display

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 0FFh unrecognized video subsystem

³40:8B³ byte ³ last diskette data rate selected

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7,6 starting data transfer rate to use

³ 0,0 500 kb/sec

³ 0,1 300 kb/sec

³ 1,0 250 kb/sec

³ 1,1 reserved

³ 5,4 last step rate selected

³ 3 ending data transfer rate to use

³ 2 reserved

³ 1 reserved

³ 0 1 combination floppy/fixed disk controller detected

³ 0 XT floppy only controller (for 360kb drive) detected

³ Data Transfer Rates

³ Kbits/sec Media Drive Sectors/Track

³ 250 360k 360k 9

³ 300 360k 1.2M 9

³ 500 1.2M 1.2M 15

³ 250 720k 720k 9

³ 250 720k 1.4M 9

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 500 1.4M 1.4M 18

³40:8C³ byte ³ hard disk status returned by controller

³40:8D³ byte ³ hard disk error returned by controller

³40:8E³ byte ³ hard disk interrupt (bit 7=working interrupt)

³40:8F³ byte ³ combo_card - status of drives 0 and 1

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 7 reserved

³ 6 drive type determined for drive 1

³ 5 drive multiple data rate capability for drive 1

³ 0 no multiple data rate

³ 1 multiple data rate

³ 4 1 then drive 1 has 80 tracks

³ 0 then drive 1 has 40 tracks

³ 3 reserved

³ 2 drive type determined for drive 0

³ 1 drive multiple data rate capability for drive 0

³ 0 no multiple data rate

³ 1 multiple data rate

³ 0 1 the drive 0 has 80 tracks

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 0 the drive 0 has 40 tracks

³40:90³4 bytes³ media state drive 0, 1, 2, 3

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ floppy_media_state

³ bit 7,6 Data transfer rate

³ 00 - 500 K/sec

³ 01 - 300 K/sec

³ 10 - 250 K/sec

³ 11 - reserved

³ 5 double stepping required

³ 4 media/drive determined

³ 3 reserved

³ 2-0 present state

³ 000 360k in 360k unestablished

³ 001 360k in 1.2M unestablished

³ 010 1.2M in 1.2M unestablished

³ 011 360k in 360k established

³ 100 360k in 1.2M established

³ 101 1.2M in 1.2M established

³ 110 reserved

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 111 none of the above

³40:94³2 bytes³ track currently seeked to drive 0, 1

³40:96³ byte ³ keyboard flag byte 3 (see int 9h)

³40:97³ byte ³ keyboard flag byte 2 (see int 9h)

³40:98³ dword ³ segment:offset pointer to users wait flag

³40:9C³ dword ³ users timeout value in microseconds

³40:A0³ byte ³ real time clock wait function in use

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bits 7 wait time elapsed and posted flag

³ 6-1 reserved

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 0 int 15h, function 86h (WAIT) has occurred

³40:A1³ byte ³ LAN A DMA channel flags

³40:A2³2 bytes³ status LAN A 0,1

³40:A4³ dword ³ saved hard disk interrupt vector

³40:A8³ dword ³ SAVE_PTR: EGA pointer to table of 7 parameters in segment:

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ offset format. Format of table:

³ D_1 dword pointer to 1472 byte table of 64 video parameters

³ D_2 dword reserved

³ D_3 dword reserved

³ D_4 dword reserved

³ D_5 dword reserved for future use

³ D_6 dword reserved for future use

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ D_7 dword reserved for future use

³40:B0³2 words³ international support (Tandy 1000 TX)

³40:B4³ byte ³ keyboard NMI control flags (Convertible)

³40:B4³ byte ³ monochrome monitor hookup detect (Tandy 1000 TX)

³ ³ ³ 00h not present 0FFh present

³40:B5³ dword ³ keyboard break pending flags (Convertible)

³40:B5³ byte ³ extended equipment detect (5 bits) (Tandy 1000 TX)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 0 = 0 drive A is 5¬

³ 1 drive A is 3«

³ 1 = 0 drive A is 5¬

³ 1 drive A is 3«

³ 2 = 0 Tandy 1000 keyboard layout

³ 1 IBM keyboard layout

³ 3 = 0 CPU slow mode

³ 1 CPU fast mode

³ 4 = 0 internal color video support enabled

³ 1 internal color video support disabled, external

³ video enabled (chg from mb'd to expansion card)

³ 5 = 0 no external monochrome video installed

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 1 external monochrome video installed

³40:B6³ byte ³ extended equipment detect (1 bit) (Tandy 1000 TX)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ bit 0 = 0 drive C is 5¬

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 1 drive C is 3«

³40:B9³ byte ³ port 60 single byte queue (Convertible)

³40:BA³ byte ³ scan code of last key (Convertible)

³40:BB³ byte ³ pointer to NMI buffer head (Convertible)

³40:BC³ byte ³ pointer to NMI buffer tail (Convertible)

³40:BD³16bytes³ NMI scan code buffer (Convertible)

³40:CE³ word ³ day counter (Convertible and after)

³ to ³ -04:8F³ end of BIOS Data Area

ÃÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ ** End of BIOS Data Area **

ÃÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³40:90³-40:EF ³ reserved by IBM

³40:F0³16bytes³ Inter-Application Communications Area (for use by applications

³40:FF³ ³ to transfer data or parameters to each other)

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ 1) Used by Turbo Power's FMARK (mark memory for TSRs).

³ 2) Used by Norton Utilities' TimeMark to store the time.

³ 3) Used by BRIEF editor.

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´

³50:00³ byte ³ DOS print screen status flag

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ 00h not active or successful completion

³ 01h print screen in progress

ÚÄÄÄÄÄÂÄÄÄÄÄÄÄ´ 0FFh error during print screen operation

³50:01³ ³ Used by BASIC

³50:02-03 ³ PCjr POST and diagnostics work area

³50:04³ byte ³ Single drive mode status byte - not used by AT&T DOS 2.11!

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ 00 logical drive A was last active

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄ´ 01 logical drive B was last active

³50:05-0E ³ PCjr POST and diagnostics work area

³50:0F³ ³ BASIC: SHELL flag (set to 02h if there is a current SHELL)

³50:10³ word ³ BASIC: segment address storage (set with DEF SEG)

³50:12³4 bytes³ BASIC: int 1Ch clock interrupt vector segment:offset storage

³50:16³4 bytes³ BASIC: int 23h ctrl-break interrupt segment:offset storage

³50:1A³4 bytes³ BASIC: int 24h disk error int vector segment:offset storage

³50:1B-1F ³ Used by BASIC for dynamic storage

³50:20-21 ³ Used by DOS for dynamic storage

³50:22-2C ³ Used by DOS for diskette parameter table. See int 1Eh for values

ÀÄÄÄÄÄÁÄÄÄÄÄÄÄ´ In DOS 1.0 this is located in the ROM BIOS, but in DOS 1.1 and

³ subsequent it is a part of DOS located at 05:22. The first byte

³ (out of eleven) of the Disk Parameter contains the hexadecimal

³ value CF in DOS 1.0 and DF in DOS 1.1 and later.

³ DOS 1.0 24ms

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄ´ DOS 1.1 26ms

³50:30-33 ³ Used by MODE command

³50:81³ ³ number of floppies installed in the system?

³50:82³ ³ first hard disk drive?

³50:83³ ³ last hard disk drive?

³50:34-FF ³ Unknown - Reserved for DOS

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Absolute Addresses .................................................... 2**6

0008:0047 IO.SYS or IBMBIO.COM IRET instruction. This is the dummy routine that

interrupts 01h, 03h, and 0Fh are initialized to during POST.

C000:001E EGA BIOS signature (the letters IBM)

F000:FA6E table of characters 00h-7Fh used by int 10h video BIOS

The first 128 characters are stored here and each occupies 8 bytes.

The high bit ones are somewhere on the video adapter card.

F000:FFF5 BIOS release date

F000:FFFE PC model identification

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ ROM BIOS Ú model byte ³

³ copyright ³ Ú submodel byte machine ³

³ date ³ ³ Ú revision ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ 00 ³ 00 ³ 00 ³ AT&T 6300, Olivetti PC ³

³ 09/02/86 ³ FA ³ 00 ³ 00 ³ PS/2 Model 30 ³

³ 01/10/86 ³ FB ³ 00 ³ 00 ³ XT-2 (early) ³

³ 01/10/86 ³ FB ³ 00 ³ 01 ³ XT Model 089 ³

³ 05/09/86 ³ FB ³ 01 ³ 02 ³ XT-2 (revised) ³

³ 01/10/84 ³ FC ³ -- ³ -- ³ AT Model 099 (original) ³

³ 06/10/85 ³ FC ³ 00 ³ 01 ³ AT Model 239 6mHz (6.6 max governor) ³

³ 11/15/85 ³ FC ³ 01 ³ 00 ³ AT Model 339, 339 8mHz (8.6 max governor) ³

³ ³ FC ³ 01 ³ 00 ³ Compaq 386/16 ³

³ ³ FC ³ 01 ³ 03 ³ some Phoenix 386 BIOS ³

³ ³ FC ³ 01 ³ 81 ³ some Phoenix 386 BIOS ³

³ 04/21/86 ³ FC ³ 02 ³ 00 ³ XT/286 ³

³ 02/13/87 ³ FC ³ 04 ³ 00 ³ PS/2 Model 50 ³

³ 02/13/87 ³ FC ³ 05 ³ 00 ³ PS/2 Model 60 ³

³ ³ FC ³ 00 ³ ³ 7531/2 Industrial AT ³

³ ³ FC ³ 06 ³ ³ 7552 "Gearbox" ³

³ 04/18/88 ³ FC ³ 04 ³ 03 ³ PS/2 50Z ³

³ 01/24/90 ³ FC ³ 01 ³ 00 ³ Compaq Deskpro 80386/25e ³

³ 10/02/89 ³ FC ³ 02 ³ 00 ³ Compaq Deskpro 386s, 386SX, 16mHz ³

³ 06/01/83 ³ FD ³ -- ³ -- ³ PCjr ³

³ 11/08/82 ³ FE ³ -- ³ -- ³ XT, Portable PC, XT/370, 3270PC ³

³ 04/24/81 ³ FF ³ -- ³ -- ³ PC-0 (16k motherboard) ³

³ 10/19/81 ³ FF ³ -- ³ -- ³ PC-1 (64k motherboard) ³

³ 08/16/82 ³ FF ³ -- ³ -- ³ PC, XT, XT/370 (256k motherboard) ³

³ 10/27/82 ³ FF ³ -- ³ -- ³ PC, XT, XT/370 (256k motherboard) ³

³ ? 1987 ³ F8 ³ 00 ³ 00 ³ PS/2 Model 80 ³

³ 3/30/87 ³ F8 ³ 00 ³ 00 ³ PS/2 Model 80-041 16mHz ³

³ 08/28/87 ³ F8 ³ ?? ³ ?? ³ PS/2 Model 80-071 16mHz ³

³ ? 1987 ³ F8 ³ 01 ³ 00 ³ PS/2 Model 80 20mHz ³

³ 09/17/87 ³ F8 ³ 01 ³ 01 ³ PS/2 Model 80-111 20mHz ³

³ ? ³ F8 ³ 04 ³ ? ³ PS/2 Model 70-121 ³

³ 01/18/89 ³ F8 ³ 0B ³ 00 ³ PS/2 Model 70 Portable ³

³ 04/11/88 ³ F8 ³ 09 ³ 02 ³ PS/2 Model 70 desktop ³

³ 02/20/89 ³ F8 ³ 0D ³ ³ PS/2 Model 70-A21 ³

³ 09/13/85 ³ F9 ³ 00 ³ 00 ³ Convertible ³

³ ³ 2D ³ -- ³ -- ³ Compaq PC (4.77mHz original) ³

³ ³ 9A ³ -- ³ -- ³ Compaq Plus (XT compatible) ³

ÀÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

The IBM PC System Interrupts (Overview) ............................... 2**7

The interrupt table is stored in the very lowest location in memory, starting

at 0000:0000h. The locations are offset from segment 0, i.e. location 0000h has

the address for int 0, etc. The table is 1024 bytes in length and contains 256

four byte vectors from 00h to 0FFh. Each address' location in memory can be

found by multiplying the interrupt number by 4. For example, int 7 could be

found by (7x4=28) or 1Bh (0000:001Bh).

These interrupt vectors normally point to ROM tables or are taken over by DOS

when an application is run. Some applications revector these interrupts to

their own code to change the way the system responds to the user. DOS provides

int 21h function 25h to change interrupts from a high level; altering the

interrupt vector table directly is not recommended, nor would it really get

you anywhere.

Quick Chart of Interrupts 00h-0FFh .................................... 2**8

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Interrupt Address ³ ³

ÃÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÙ Function ³

³ Number³ (Hex) ³ Type ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0 ³ 00-03 ³ CPU ³ Divide by Zero ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1 ³ 04-07 ³ CPU ³ Single Step ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 2 ³ 08-0B ³ CPU ³ Nonmaskable ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 3 ³ 0C-0F ³ CPU ³ Breakpoint ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 4 ³ 10-13 ³ CPU ³ Overflow ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 5 ³ 14-17 ³ BIOS³ Print Screen ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 6 ³ 18-1B ³ hdw ³ Reserved ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 7 ³ 1C-1F ³ hdw ³ Reserved ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 8 ³ 20-23 ³ hdw ³ Time of Day ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 9 ³ 24-27 ³ hdw ³ Keyboard ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ A ³ 28-2B ³ hdw ³ Reserved ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ B ³ 2C-2F ³ hdw ³ Communications (8259) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ C ³ 30-33 ³ hdw ³ Communications ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ D ³ 34-37 ³ hdw ³ Disk ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ E ³ 38-3B ³ hdw ³ Diskette ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F ³ 3C-3F ³ hdw ³ Printer ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 10 ³ 40-43 ³ BIOS³ Video ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 11 ³ 44-47 ³ BIOS³ Equipment Check ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 12 ³ 48-4B ³ BIOS³ Memory ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 13 ³ 4C-4F ³ BIOS³ Diskette/Disk ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 14 ³ 50-53 ³ BIOS³ Serial Communications ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 15 ³ 54-57 ³ BIOS³ Cassette, System Services ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 16 ³ 58-5B ³ BIOS³ Keyboard ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 17 ³ 5C-5F ³ BIOS³ Parallel Printer ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 18 ³ 60-63 ³ BIOS³ ROM BASIC Loader ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 19 ³ 64-67 ³ BIOS³ Bootstrap Loader ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1A ³ 68-6B ³ BIOS³ Time of Day ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1B ³ 6C-6F ³ BIOS³ Keyboard Break ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1C ³ 70-73 ³ BIOS³ Timer Tick ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1D ³ 74-77 ³ BIOS³ Video Initialization ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1E ³ 78-7B ³ BIOS³ Diskette Parameters ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1F ³ 7C-7F ³ BIOS³ Video Graphics Characters, second set ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 20 ³ 80-83 ³ DOS ³ General Program Termination ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 21 ³ 84-87 ³ DOS ³ DOS Services Function Request ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 22 ³ 88-8B ³ DOS ³ Called Program Termination Address ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 23 ³ 8C-8F ³ DOS ³ Control Break Termination Address ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 24 ³ 90-93 ³ DOS ³ Critical Error Handler ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 25 ³ 94-97 ³ DOS ³ Absolute Disk Read ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 26 ³ 98-9B ³ DOS ³ Absolute Disk Write ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 27 ³ 9C-9F ³ DOS ³ Terminate and Stay Resident ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 28-3F ³ A0-FF ³ DOS ³ Reserved for DOS ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ *29h Fast Screen Write ³

³ *2Ah Microsoft Networks - Session Layer Interrupt ³

³ 2Fh Multiplex Interrupt ³

³ *30h Far jump instruction for CP/M-style calls ³

³ 33h Used by Microsoft Mouse Driver ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 40-43 ³100-115³ BIOS³ Reserved for BIOS ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 40h Hard Disk BIOS ³

³ 41h Hard Disk Parameters (except PC1) ³

³ 42h Pointer to screen BIOS entry (EGA, VGA, PS/2) ³

³ 43h Pointer to EGA initialization parameter table ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 44 ³116-119³ BIOS³ First 128 Graphics Characters ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 45-47 ³120-131³ BIOS³ Reserved for BIOS ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 45h Reserved by IBM (not initialized) ³

³ 46h Pointer to hard disk 2 params (AT, PS/2) ³

³ 47h Reserved by IBM (not initialized) ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 48 ³132-135³ BIOS³ PCjr Cordless Keyboard Translation ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 49 ³136-139³ BIOS³ PCjr Non-Keyboard Scancode Translation Table ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 4Ah Real-Time Clock Alarm (Convertible, PS/2) ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 50-5F ³140-17F³ BIOS³ Reserved for BIOS ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 5Ah Cluster Adapter BIOS entry address ³

³ *5Bh IBM (cluster adapter?) ³

³ 5Ch NETBIOS interface entry port ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 60-67 ³180-19F³ User Program Interrupts (availible for general use) ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 60h 10-Net Network ³

³ 67h Used by LIM & AQA EMS, EEMS ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 68-7F ³1A0-1FF³ Reserved by IBM ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 6Ch System Resume Vector (Convertible) ³

³ 6Fh some Novell and 10-Net API functions ³

³ 70h IRQ 8, Real Time Clock Interrupt (AT, PS/2) ³

³ 71h IRQ 9, LAN Adapter 1 ³

³ 72h IRQ 10 (AT, XT/286, PS/2) Reserved ³

³ 73h IRQ 11 (AT, XT/286, PS/2) Reserved ³

³ 74h IRQ 12 Mouse Interrupt (PS/2) ³

³ 75h IRQ 13, Coprocessor Error ³

³ 76h IRQ 14, Hard Disk Controller (AT, PS/2) ³

³ 77h IRQ 15 (AT, XT/286, PS/2) Reserved ³

³ 7Ch IBM REXX88PC command language ³

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 80-85 ³200-217³ ROM BASIC ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 86-F0 ³218-3C3³ Used by BASIC Interpreter When BASIC is running ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F1-FF ³3C4-3FF³ Reserved by IBM ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ *0F8h Set Shell Interrupt (OEM) ³

³ *0F9h OEM SHELL service codes ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

The IBM-PC System Interrupts (in detail) .............................. 2**9

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 00h Divide by Zero ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0000h) (processor error). Automatically called at end of DIV or IDIV

operation that results in error. Normally set by DOS to display an

error message and abort the program.

note On an 8086/8088, the return address points to the following instruction

On an 80286/80386, the return address points to the divide instruction

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³Interrupt 01h Single step ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0004h) Taken after every instruction when CPU Trap Flag indicates

single-step mode (bit 8 of FLAGS is 1). This is what makes the "T"

command of DEBUG work for single stepping. Is not generated after MOV

to segment register or POP of segment register. (unless you have a

very early 8088 with the microcode bug).

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³Interrupt 02h Non-maskable interrupt ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0008h) Vector not disabled via CLI. Generated by NMI signal in

hardware. This function is called in the event of a memory

parity error or may occur in the event of other hardware

problems or failures depending on the specific manufacturer's

hardware. Displays the appropriate error message and halts the

processor.

Some AT chip sets apparently use int 02h to signal I/O errors

as well as parity errors.

This signal has various uses:

POST parity error: all except PCjr and Convertible

80x87 coprocessor interrupt: all except PCjr and Convertible

Keyboard interrupt: PCjr, Convertible

I/O channel check: Convertible, PS/2 50+

Disk controller power-on request: Convertible

System suspend: Convertible

Realtime clock: Convertible

System watchdog timer: PS/2 50+

Timeout interrupt: PS/2 50+

DMA timer time-out interrupt: PS/2 50+

Infrared keyboard link: PCjr

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³Interrupt 03h Breakpoint ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:000Ch) Taken when CPU executes the 1-byte int 3 (0CCh). Similar to 8080's

(internal) RST instruction. Generally used to set breakpoints for DEBUG.

note 1) Also used by Turbo Pascal versions 1,2,3 when {$U+} specified.

2) Int 3s are sometimes inserted by the Microsoft Linker in response to

an unresolved symbol.

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³Interrupt 04h Divide overflow ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0010h) Generated by INTO instruction if OF flag is set. If flag is not set,

(internal) INTO is effectively a NOP. Used to trap any arithmetic errors when

program is ready to handle them rather than immediately when they

occur.

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³Interrupt 05h Print Screen ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0014h) Service dumps the screen to the printer. Invoked by int 9 for shifted

key 55 (PrtSc). Automatically called by keyboard scan when PrtSc key

is pressed. Normally executes a routine to print the screen, but may

call any routine that can safely be executed from inside the keyboard

handler. Status and result byte are at address 0050:0000.

(internal) BOUND Check Failed (80286+)

Generated by BOUND instruction when the value to be tested is less

than the indicated lower bound or greater than the indicated upper

bound.

entry AH 05h

return absolute address 50:0

00h print screen has not been called, or upon return from a call

there were no errors

01h print screen is already in progress

0FFh error encountered during printing

note 1) Uses BIOS services to read the screen.

2) Output is directed to LPT1.

3) Revectored into GRAPHICS.COM if GRAPHICS.COM is loaded.

4) On the Tandy 1000TX this interrupt can be enabled or disabled across

the expansion slots via a DIP switch.

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³Interrupt 06h Reserved by IBM ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0018h)

On the Tandy 1000TX this interrupt can be enabled or disabled across

the expansion slots via a DIP switch.

(internal) Undefined Opcode (80286+)

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³Interrupt 07h Reserved by IBM ³

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(0:00C0h)

On the Tandy 1000TX this interrupt can be enabled or disabled across

the expansion slots via a DIP switch.

(internal) No Math Unit Available (80286+)

note The 80286 and later can be programmed to generate an int 7 whenever

an ESC instruction is encountered. This could be used to emulate an

80x87 series coprocessor in software and be transparent to the

application software. It could also be used to make a non-Intel

floating point processor emulate an 80x87.

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³Interrupt 08h Timer ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0020h) 55ms timer "tick" issued 18.2 times per second.

(IRQ0) 8259-1 Interrupt Controller

Updates the system time at [0040:006C] (low word) and [0040:006E]

(high word) and issues an int 1Ch (timer). (int 1Ch points to an

IRET instruction unless changed by a resident program). The timer

interrupt is given the highest maskable interrupt priority upon

power up.

(internal) Double Fault (80286+ protected mode) Called when multiple exceptions

occur on one instruction, or an exception occurs in an exception

handler. If an exception occurs in the double fault handler, the CPU

goes into SHUTDOWN mode (which circuitry in the PC/AT converts to a

reset).

entry AH 08h

return absolute addresses:

40:6C number of interrupts since power on (4 bytes)

40:70 number of days since power on (1 byte)

40:67 day counter on all products after AT

40:40 motor control count - gets decremented and shuts off diskette

motor if zero

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³Interrupt 09h Keyboard ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0024h) Taken whenever a key is pressed or released. This is normally a scan

(IRQ1) code, but may also be an ACK or NAK of a command on AT-type

keyboards. The hardware provides the key pressed in a non-ASCII scan

code format read at I/O port 60h. The servicer acknowledges receipt

of the key by toggling bit 7 of port 61h. (Port 61h should be read

first, then bit 7 ORed on, output to port 61h, then ANDed off, and

resent to port 61h).

The read key is decoded to yield an ASCII character, special

function key (such as F1) or a control function like Left Shift Key.

The converted ASCII character is placed into the next available

position in the circular queue keyboard. It is put in the position

indicated by queue tail when it will not cause the loss of earlier

entered data. The queue head points to the oldest key pressed in the

buffer which has not been removed from the queue (the normal process

uses int 16h to remove keys from the queue and return the key value

to the int 16h caller).

The 16 word queue holds up to 16 keys. If the queue head equals the

queue tail, the queue is empty. Valid keys in the queue comprise

the upper byte scan code and the lower byte ASCII character. If the

key pressed has no ASCII equivalent (i.e F1 to F12), the lower byte

is zero.

Toggle and shift keys are not placed in the buffer, but appear in

the two status bytes at absolute addr. [0040:0017,18].

Special key combinations will cause other events to occur:

a) Ctrl-Alt_Del - Reset computer by jumping to power_on_reset

b) Print screen - Call int_5_prn_scrn to print the current screen

c) Ctrl-Break - Call int_1Bh control break key processor (DOS)

d) Pause - Wait until an ASCII key is pressed, without

placing the key in the queue

(internal) Math Unit Protection Fault (80286+ protected mode)

entry AH 09h

return at absolute memory addresses:

40:17 bit

0 right shift key depressed

1 left shift key depressed

2 control key depressed

3 alt key depressed

4 ScrollLock state has been toggled

5 NumLock state has been toggled

6 CapsLock state has been toggled

7 insert state is active

40:18 bit

0 left control key depressed

1 left alt key depressed

2 SysReq key depressed

3 Pause key has been toggled

4 ScrollLock key is depressed

5 NumLock key is depressed

6 CapsLock key is depressed

7 Insert key is depressed

40:96 bit

0 last code was the E1h hidden code

1 last code was the E0h hidden code

2 right control key down

3 right alt key down

4 101 key Enhanced keyboard installed

5 force NumLock if rd ID & kbx

6 last character was first ID character

7 doing a read ID (must be bit 0)

40:97 bit

0 ScrollLock indicator

1 NumLock indicator

2 CapsLock indicator

3 circus system indicator

4 ACK received

5 resend received flag

6 mode indicator update

7 keyboard transmit error flag

40:1E keyboard buffer (20h bytes)

40:1C buffer tail pointer

40:72 1234h if ctrl-alt-del pressed on keyboard

AL scan code

note 1) Int 05h invoked if PrtSc key pressed.

2) Int 1Bh invoked if Ctrl-Break key sequence pressed.

3) Int 15h, AH=85h invoked on AT and after if SysReq key is pressed.

4) Int 15h, AH=4Fh invoked on machines after AT.

5) Int 16h, BIOS keyboard functions, uses this interrupt.

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³Interrupt 0Ah EGA Vertical Retrace ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0028h) used by EGA vertical retrace

(IRQ2) 8259-1 Interrupt Controller

note 1) The TOPS and PCnet adapters use this IRQ line by default.

2) On systems equipped with 2 interrupt controller chips (8259), IRQ 2

is used to support the second interrupt controller. In this case,

int 71h (IRQ 9) is used to replace IRQ 2. Hardware calls to int 71h

are redirected to this interrupt to maintain compatibility.

3) Many VGA boards to not use this interrupt.

(internal) Invalid Task State Segment (80286+ protected mode)

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³Interrupt 0Bh Communications Controller (serial port) hdw. entry ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:002Ch) Serial Port 2 (COM2) 8259-1

(IRQ3)

note 1) IRQ 3 may be used by SDLC (synchronous data-link control) or

bisynchronous communications cards instead of a serial port.

2) The TOPS and PCnet adapters use this interrupt request line as an

alternate.

3) On PS/2s, COM2 through COM8 share this IRQ.

4) For most serial boards, COM4 shares this IRQ.

5) On the Commodore Amiga 2000 with the PC Bridge Board, this interrupt

is used for communication between the Amiga system board and the

Bridge Board. This was probably the lowest IRQ level they felt safe

using, but limits the A2000's use of network cards, etc.

6) This interrupt is used by part of the stack-switching code added

to DOS 3.2 for use with Local Area Network adapters.

7) The PS/2 puts COM3 through COM8 at port addresses above 3FFh (not

properly decoded by older PCs) and has all of them sharing IRQ3.

(internal) Not Present (80286+ protected mode)

Generated when loading a segment register if the segment descriptor

indicates that the segment is not currently in memory. May be used

to implement virtual memory.

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³Interrupt 0Ch Communications Controller (serial port) Hardware Entry ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0030h) Serial Port 1 (COM1) or internal modem in PCjr or Convertible

(IRQ4) 8259-1

note 1) IRQ 4 may be used by SDLC (synchronous data-link control) or

bisynchronous communications cards instead of a serial port.

2) On some PCs, this interrupt is shared by COM3.

3) Tandy computers use IRQ4 instead of IRQ5 for the hard disk interrupt.

4) Best performance of mice sometimes happens when they are configured

for IRQ4 instead of IRQ3, since some mouse drivers may lock system

interrupts for long periods.

(internal) Stack Fault (80286+ protected mode)

Generated on stack overflow/underflow. Note that the 80286 will shut

down in real mode if SP=1 before a push.

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³Interrupt 0Dh Hard Disk ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0034h) Miscelleneous uses

(IRQ5) 8259-1

note 1) Various Tandy 1000 models may use this line for the 60Hhz RAM refresh

or as "optional bus interrupt."

2) Used by hard disk on IBM XT and most compatibles.

3) LPT2 on AT, XT/286, and PS/2

4) Dummy CRT vertical retrace on PCjr

(internal) General Protection Violation (80286+)

Called in real mode when an instruction attempts to access a word

operand located at offset 0FFFFh or a PUSH MEM or POP MEM

instruction contains an invalid bit code in the second byte, or

when an instruction exceeds the maximum length allowed (10 bytes

for 80286, 15 bytes for 80386)

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³Interrupt 0Eh Diskette Interrupt ³

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(0:0038h) Generated by floppy controller on completion of an operation

(IRQ6) (sets bit 8 of 40:3E)

(internal) Page Fault (80386+ native mode)

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³Interrupt 0Fh Reserved by IBM ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:003Ch) IRQ7 used by 8259 PPI interrupt (LPT1, LPT2)

(IRQ7)

note 1) Generated by the LPT1 printer adapter when printer becomes ready. Many

printer adapters do not reliably generate this interrupt.

2) This interrupt is normally avoided. If a bad interrupt occurs, it will

vector to this spot (when caused by a misprogrammed 8259 PIC)

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

C H A P T E R T H R E E

THE PC ROM BIOS - Interrupts 10h through 19h

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³Interrupt 10h Video I/O - services to handle video output ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0040h) The ROM video routines in the original PC BIOS are designed for

use with the Color Graphics Adapter and incorporate code to test

for the horizontal retrace before writing. The check is

performed no matter what actual display adapter is installed.

The ROM character table for the first 128 characters is located

at 0FA6Eh in the PC. Int 01Fh can be used to point to a second

table of 128 characters.

CS, SS, DS, ES, BX, CX, DX are preserved during call. All

others are destroyed.

Function 00h Determine or Set Video State

entry AH 00h set video mode

AL display mode: CGA|PCjr|MDA|MCGA|EGA|VGA|8514

16 color 40x25, 360x400 graphics | | | | |VGA|

16 color 80x25 720x400 graphics | | | |VGA| |

16 color 03h 80x25 color text CGA|PCjr| | |EGA|VGA|

monochrome 07h 80x25 monochrome text | |MDA| |EGA| |

N/A 0Bh BIOS font load | | | |EGA|VGA|

N/A 0Ch BIOS font load | | | |EGA|VGA|

16 color 0Dh 320x200 graphics | | | |EGA|VGA|

16 color 0Eh 640x200 graphics | | | |EGA|VGA|

monochrome 0Fh 640x350 graphics | | | |EGA|VGA|

16 & 64 color 10h 640x350 color hi-res | | | |EGA|VGA|

16 color 12h 640x480 graphics | | | | |VGA|

256 color 13h 320x200 graphics | | |MCGA| |VGA|8514

14h-20h used by EGA and VGA graphics modes

18h 132x44 8x8 char mono | Tseng Labs EVA

19h 132x25 8x14 char mono | Tseng Labs EVA

1Ah 132x28 8x13 char mono | Tseng Labs EVA

monochrome 21h Hercules Graphics, Graphics Page 1

monochrome 22h Hercules Graphics, Graphics Page 2

22h 132x44 | Tseng, Ahead

23h 132x25 | Tseng Labs EVA

132x25 | Ahead Systems EGA2001

132x25 | ATI EGA Wonder

24h 132x28 | Tseng Labs EVA

25h 80x60 640x480 | Tseng Labs EVA

16 color 640x480 | VEGA VGA

26h 80x60 | Tseng Labs EVA

80x60 640x480 | Ahead Systems EGA2001

16 color 27h 720x512 | VEGA VGA

monochrome 132x25 | ATI EGA Wonder

28h unknown | VEGA VGA

16 color 29h 800x600 | VEGA VGA

256 color 2Dh 640x350 | VEGA VGA

256 color 2Eh 640x480 | VEGA VGA

256 color 2Fh 720x512 | VEGA VGA

256 color 30h 800x600 | VEGA VGA

unknown | AT&T 6300

16 color 36h 960x720 | VEGA VGA

16 color 37h 1024x768 | VEGA VGA

monochrome 132x44 | ATI EGA Wonder

2 color 40h 640x400 | AT&T 6300

80x43 | VEGA VGA

16 color 41h 640x200 | AT&T 6300

132x25 | VEGA VGA

16 color 42h 640x400 | AT&T 6300

132x43 | VEGA VGA

43h unsupported 640x200 of 640x400 viewport AT&T 6300

80x60 | VEGA VGA

44h disable VDC and DEB output | AT&T 6300

100x60 | VEGA VGA

48h 80x50 640x400 | AT&T 6300

4Dh 120x25 | VEGA VGA

4Eh 120x43 | VEGA VGA

4Fh 132x25 | VEGA VGA

monochrome 50h 132x25 | Ahead Systems EGA2001

16 color 640x480 | Paradise EGA-480

monochrome 80x43 | VEGA VGA

640x480 mono? | Taxan 565 EGA

51h 80x30 | Paradise EGA-480

monochrome 132x25 | VEGA VGA

640x480 ? | ATI EGA Wonder

monochrome 52h 132x44 | Ahead Systems EGA2001

monochrome 132x43 | VEGA VGA

752x410 ? | ATI EGA Wonder

53h 800x560 ? | ATI EGA Wonder

54h 132x43 | Paradise EGA-480

16 color 132x43 | Paradise VGA

16 color 132x43 | Paradise VGA on multisync

132x43 | Taxan 565 EGA

55h 132x25 | Paradise EGA-480

16 color 132x25 | Paradise VGA

16 color 132x25 | Paradise VGA on multisync

132x25 | Taxan 565 EGA

56h 132x43 | NSI Smart EGA+

132x43 | Paradise VGA

132x43 | Paradise VGA on multisync

monochrome 132x43 | Taxan 565 EGA

57h 132x25 | NSI Smart EGA+

132x25 | Paradise VGA

132x25 | Paradise VGA on multisync

monochrome 132x25 | Taxan 565 EGA

58h 100x75 800x600 16/256k | Paradise VGA

59h 100x75 800x600 | Paradise VGA

5Eh 640x400 | Paradise VGA,VEGA VGA

5Fh 640x480 | Paradise VGA

60h 80x? ?x400 | Corona/Cordata BIOS v4.10+

752x410 | VEGA VGA

60h 400 line graphics+80 col text |(Corona/Cordata)

61h 400 line graphics | Corona/Cordata BIOS v4.10+

720x540 | VEGA VGA

62h 800x600 | VEGA VGA

16 color 71h 100x35 800x600 | NSI Smart EGA+

74h 640x400 graphics | Toshiba 3100

7Eh Special Mode Set | Paradise VGA (see below)

BX horizontal dimension of the mode desired

CX vertical dimension of the mode desired

(both BX/CX in pixels for graphics modes, rows

for text modes)

DX number of colors of the mode desired

(use 0 for monochrome modes)

return BH 7Eh if successful

7Fh Special Function Set | Paradise VGA (see below)

BH 00h Set VGA Operation

01h Set Non-VGA Operation

02h Query Mode Status

return BL 0 if operating in VGA mode

1 if non-VGA mode.

CH total video RAM size in 64k byte units

CL video RAM used by the current mode

03h Lock Current Mode

Allows current mode (VGA or non-VGA) to

survive reboot.

BH 0Ah,0Bh,0Ch,0Dh,0Eh,0Fh

write paradise registers 0,1,2,3,4,5

(port 03CEh indexes A,B,C,D,E,F)

BL value to set in the paradise register.

BH 1Ah,1Bh,1Ch,1Dh,1Eh,1Fh

read paradise registers 0,1,2,3,4,5

(port 03CEh indexes A,B,C,D,E,F)

return BL value of the Paradise register

BH 7Fh if successful.

note Color modes (0,1,2,3,4,5,6) will set non-VGA CGA

operation. Monochrome mode 7 will set non-VGA

MDA/Hercules operation.

82h 80x25 B&W | AT&T VDC overlay mode *

83h 80x25 | AT&T VDC overlay mode *

86h 640x200 B&W | AT&T VDC overlay mode *

C0h 640x400 2/prog pallet | AT&T VDC overlay mode *

C4h disable output | AT&T VDC overlay mode *

D0h 640x400 | DEC VAXmate AT&T mode

unknown 640x225 | Z-100

unknown 640x400 | Z-100

note 1) If the high bit in AL is set, the display buffer is not cleared when a

new mode is selected. This may be used to mix modes on the display;

for example, characters of two difference sizes might be displayed

2) Modes 8-10 are available on the PCjr, Tandy 1000, and PS/2

3) IBM claims 100% software and hardware emulation of the CGA with the

MCGA chipset. All registers may be read and written as CGA. All

characters are double-scanned to give 80x25 with 400 line resolution.

The attributes for setting border color may be set on MCGA, but the

borders will remain the default color (they cannot actually be set)

4) The IBM Color Graphics Adapter (CGA) is too slow for the screen to

be updated before the vertical retrace of the monitor is completed.

If the video RAM is addressed directly, the screen will have "snow"

or interference. IBM's default is to turn the adapter off when it is

being updated, ie "flickering" when the display is scrolled.

5) The vertical retrace signal may be ignored when using the MCGA adapter.

The MCGA will not generate snow when written to. There is no flicker

with the MCGA.

6) The PCjr Video Gate Array uses a user-defined block of main system RAM

from 4 to 32k in size instead of having dedicated memory for the

display. Vertical retrace may be ignored when writing to the PCjr.

There is no flicker with the PCjr display.

7) The Hercules Graphics Card has 750x348 resolution

8) The Hercules Graphics Card takes 64k beginning at B:000 (same as MDA)

9) The CGA, MCGA, and VGA adapters use hardware address B:800

10) The BIOS clears the screen when the mode is set or reset.

11) For AT&T VDC overlay modes, BL contains the DEB mode, which may be 06h,

40h, or 44h

12) Int 10 will take the shapes of the first 128 characters (00h-7Fh) from

the table located in ROM at absolute address F000:FA6E. The EGA and VGA

have hardware capability to change this.

Function 01h Set Cursor Type - set the size of the cursor or turn it off

entry AH 01h

CH bit values:

bits 0-4 top line for cursor in character cell

bits 5-6 blink attribute

00 normal

01 invisible (no cursor)

10 slow (not used on original IBM PC)

11 fast

CL bit values:

bits 0-4 bottom line for cursor in character cell

return none

note 1) The ROM BIOS default cursors are: start end

monochrome mode 07h: 11 12

text modes 00h-03h: 6 7

2) The blinking in text mode is caused by hardware and cannot be turned

off, though some kludges can temporarily fake a nonblinking cursor

3) The cursor is automatically turned off in graphics mode

4) Another method of turning off the cursor in text mode is to position it

to a nondisplayable address, such as (X,Y)=(0,25)

5) Buggy on EGA systems - BIOS remaps cursor shape in 43 line modes, but

returns unmapped cursor shape

Function 02h Set Cursor Position - reposition the cursor to (X,Y)

entry AH 02h

BH video page

00h graphics mode

03h modes 2 and 3

07h modes 0 and 1

DH row (Y=0-24)

DL column (X=0-79 or 0-39)

return none

note 1) (0,0) is upper left corner of the screen

Function 03h Read Cursor Position - return the position of the cursor

entry AH 03h

BH page number

00h in graphics modes

03h in modes 2 & 3

07h in modes 0 & 1

return CH top line for cursor (bits 4-0)

CL bottom line for cursor (bits 4-0)

DH row number (Y=0-24)

DL column number (X=0-79 or 0-39)

Function 04h Read Light Pen - fetch light pen information

entry AH 04h

return AH 00h light pen not triggered

AH 01h light pen is triggered, values in resgisters

BX pixel column (X=0-319 or 0-639) graphics mode

CH raster line (Y=0-199) old graphics modes

CX (EGA) raster line (0-nnn) new graphics modes

DH row of current position (Y=0-24) text mode

DL column of current position (X=0-79 or 0-39) text mode

note Not supported on PS/2

Function 05h Select Active Page - set page number for services 6 and 7

entry AH 05h

AL number of new active page

0-7 modes 00h and 01h (CGA)

0-3 modes 02h and 03h (CGA)

0-7 modes 02h and 03h (EGA)

0-7 mode 0Dh (EGA)

0-3 mode 0Eh (EGA)

0-1 mode 0Fh (EGA)

0-1 mode 10h (EGA)

0 set address of graphics bitmap buffer (modes 60h,61h)

BX segment of buffer

0Fh get address of graphics bitmap buffer (modes 60h,61h)

BX segment of buffer

for PCjr only:

AL 80h to read CRT/CPU page registers

81h to set CPU page register to value in BL

82h to set CRT page register to value in BH

83h to set both CPU and page registers

(and Corona/Cordata BIOS v4.10+)

BH CRT page number for subfunctions 82h and 83h

BL CPU page register for subfunctions 81h and 83h

return standard PC none

PCjr if called with AH bit 7=1 then

BH CRT page register (if AL >= 80h)

BL CPU page register (if AL >= 80h)

DX segment of graphics bitmap buffer (video modes 60h,61h; AL=0Fh)

note 1) Mono adapter has only one display page

2) CGA has four 80x25 text pages or eight 40x25 text pages

3) A separate cursor is maintained for each display page

4) Switching between pages does not affect their contents

5) Higher page numbers indicate higher memory positions

Function 06h Scroll Page Up - scroll up or clear a display "window"

entry AH 06h

AL number of lines blanked at bottom of page

0 = blank entire window

BH attributes to be used on blank line

CH row (Y) of upper left corner or window

CL column (X) of upper left corner of window

DH row (Y) of lower right corner of window

DL column (X) of lower right corner of window

return none

note 1) Push BP before scrolling, pop after

2) If in CGA text mode, affects current page only

Function 07h Scroll Page Down - scroll down or clear a display "window"

entry AH 07h

AL number of lines to be blanked at top of page

0 = blank entire window

BH attributes to be used on blank line

CH row (Y) of upper left corner or window

CL column (X) of upper left corner of window

DH row (Y) of lower right corner of window

DL column (X) of lower right corner of window

return none

note 1) Push BP before scrolling, pop after

2) If in CGA text mode, affects current page only

Function 08h Read Character Attribute - of character at current cursor pos.

entry AH 08h

BH display page number - text mode

return AH character attribute - text mode

AL ASCII code of character at current cursor position

Function 09h Write Character and Attribute - at current cursor position

entry AH 09h

AL ASCII code of character to display

BH display page number - text mode

BL attribute/color of character

CX number of characters to write

return none

note 1) CX should not exceed actual rows availible, or results may be erratic

2) Setting CX to zero will cause runaway

3) All values of AL result in some sort of display; the various control

characters are not recognized as special and do not change the current

cursor position

4) Does not change cursor position when called - the cursor must be

advanced with int 10 function 0Ah.

5) If used to write characters in graphics mode with bit 7 of AH set to 1

the character will by XORed with the current display contents.

6) In graphics mode the bit patterns for ASCII character codes 80h-0FFh

are obtained from a table. On the standard PC and AT, the location is at

interrupt vector 01Fh (0000:007C). For ASCII characters 00h-07Fh, the

table is at an address in ROM. On the PCjr the table is at interrupt

vector 44h (0000:00110) and is in addressable RAM (may be replaced by

the user)

7) All characters are displayed, including CR, LF, and BS

Function 0Ah Write Character - display character(s) (use current attribute)

entry AH 0Ah

AL ASCII code of character to display

BH display page - text mode

BL color of character (graphics mode, PCjr only)

CX number of times to write character

return none

note 1) CX should not exceed actual rows availible, or results may be erratic

2) All values of AL result in some sort of display; the various control

characters are not recognized as special and do not change the current

cursor position

3) If used to write characters in graphics mode with bit 7 of AH set to 1

the character will by XORed with the current display contents.

4) In graphics mode the bit patterns for ASCII character codes 80h-0FFh

are obtained from a table. On the standard PC and AT, the location is at

interrupt vector 01Fh (0000:007C). For ASCII characters 00h-07Fh, the

table is at an address in ROM. On the PCjr the table is at interrupt

vector 44h (0000:00110) and is in addressable RAM (may be replaced by

the user)

5) In EGA in graphics modes, replication count in CX works correctly only

if all characters written are contained on the same row

6) All characters are displayed, including CR, LF, and BS

Function 0Bh Set Color Palette - set palette for graphics or text border

entry AH 0Bh

BH 00h select border (text mode)

BL color 0-15, 16-31 for high-intensity characters

BH 01h set graphics palette with value in BL

(CGA) BL 0 green/red/yellow

1 cyan/magenta/white

(EGA) (graphics modes)

BH 0

BL has border color (0-15) & high intensity bkgr'd color (16-31)

BH 1

BL contains palette being selected (0-1)

return none

note 1) Valid in CGA mode 04h, PCjr modes 06h, 08h-0Ah

2) Although the registers in the MCGA may be set as if to change the

border, the MCGA will not display a border no matter what register

settings are used.

Function 0Ch Write Dot - plot one graphics pixel

entry AH 0Ch

AL dot color code (0/1 in mode 6, 0-3 in modes 4 and 5)

(set bit 7 to XOR the dot with current color)

0-3 mode 04h, 05h

0-1 mode 06h

BH page number (ignored if adapter supports only one page)

CX column (X=0000h - 027Fh)

(0 - 319 in modes 4,5,13, 0 - 639 in modes 6,14,15,16)

DX row (Y=0000h - 00C7h) (0 - 199 CGA)

return none

note Video graphics modes 4-6 only

Function 0Dh Read Dot - determine the color of one graphics pixel

entry AH 0Dh

CX column (X=0000h - 027Fh) (0-319 or 639)

DX row (Y=0000h - 00C7h) (0-199)

return AL color of dot

note Only valid in graphics mode

Function 0Eh Write TTY - write one character and update cursor. Also handles

CR (0Dh), beep (07h), backspace (10h), and scrolling

entry AH 0Eh

AL ASCII code of character to be written

BH page number (text)

BL foreground color (video modes 6 & 7 only) (graphics)

return none

note 1) The ASCII codes for bell, backspace, carriage return, and linefeed are

recognized and appropriate action taken. All other characters are

written to the screen and the cursor is advanced to the next position

2) Text can be written to any CGA page regardless of current active page

3) Automatic linewrap and scrolling are provided through this function

4) This is the function used by the DOS CON console driver.

5) This function does not explicitly allow the use of attributes to the

characters written. Attributes may be provided by first writing an ASCII

27h (blank) with the desired attributes using function 09h, then

overwriting with the actual character using this function. While clumsy

this allows use of the linewrap and scrolling services provided by

this function

Function 0Fh Return Current Video State - mode and size of the screen

entry AH 0Fh

return AH number of character columns on screen

AL mode currently set (see AH=00h for display mode codes)

BH current active display page

note If mode was set with bit 7 set ("no blanking"), the returned mode will

also have bit 7 set

Function 10h Set Palette Registers (PCjr, Tandy 1000, EGA, MCGA, VGA)

entry AH 10h

AL 00h set individual palette register

BH color value to store

BL palette register to set

(on MCGA, only BX = 0712h is supported)

01h set border color palette register

BH color value to store

02h set all palette registers and overscan

ES:DX pointer to 17-byte list

bytes 0-15 values for palette regs. 0-15

byte 16 value for border color register

03h toggle blink/intensity bit (Jr, EGA, MCGA, VGA)

BL 00h enable intensity

01h enable blink

04h unknown

05h unknown

06h unknown

07h read individual palette register (VGA)

BL palette register number

return BH palette register value

08h read overscan (order color) register (VGA)

return BH value

09h read all palette registers and overscan register (VGA)

ES:DX pointer to buffer address (17 bytes)

10h set individual video DAC color register (MCGA, VGA)

BX register number

CH new value for green (0-63)

CL new value for blue (0-63)

DH new value for red (0-63)

11h unknown

12h set block of video DAC color registers (MCGA, VGA)

BX starting color register

CX number of registers to set

ES:DX table of 3*CX bytes where each 3 byte group

represents one byte each of red, green and

blue (0-63)

13h set video DAC color page (VGA)

BH 00h select 4 blocks of 64

BH 01h select 16 blocks of 16

BL 00h select paging mode

BL 01h select Page

BH page number (00h to 03h) or (00h to 0Fh)

(not valid in mode 13h)

14h unknown

15h read individual video DAC color register (MCGA, VGA)

BL palette register number

return DH red value

CH green value

CL blue value

16h unknown

17h read block of video DAC color registers (MCGA, VGA)

BX starting palette register

CX number of palette registers to read

ES:DX buffer (3 * CX bytes in size)

return CX number of red, green and blue triples in buffer

18h *UNDOCUMENTED* set PEL mask

BL new PEL value

19h *UNDOCUMENTED* read PEL mask

BL value read

1Ah read video DAC color-page state (VGA)

return BL paging mode

0 four pages of 64

1 sixteen pages of 16

BH current page

1Bh perform gray-scale summing (MCGA, VGA)

BX starting palette register

CX number of registers to convert

BH color value

BL if AL=00h palette register to set (00h-0Fh)

if AL=03h 0 to enable intensity

1 to enable blinking

ES:DX if AL=02h pointer to 16-byte table of register values

followed by the overscan value:

bytes 0-15 values for palette registers 0-15

byte 16 value for border register

return none

note DAC is Digital to Analog Convertor circuit in MCGA/VGA chips

Function 11h Character Generator Routine (EGA and after)

entry AH 11h

The following functions will cause a mode set, completely

resetting the video environment, but without clearing the video

buffer.

AL 00h, 10h load user-specified patterns

BH number of bytes per character pattern

BL block to load in map 2

CX count of patterns to store

DX character offset into map 2 block

ES:BP pointer to user table

01h, 11h load ROM monochrome patterns (8 by 14)

BL block to load

02h, 12h load ROM 8 by 8 double-dot patterns

BL block to load

03h set block specifier

BL block specifier

(EGA/MCGA) bits 0,1 = block selected by chars with attribute

bit 3 = 0

bits 2,3 = block selected by chars with attribute

bit 3 = 1

(VGA) bits 0,1,4 = block selected by attribute bit 3 = 0

bits 2,3,5 = block selected by attribute bit 3 = 1

04h,14h load 8x16 text character set (MCGA, VGA)

The routines called with AL=1x are designed to be

called only immediately after a mode set and are

similar to the routines called with AL=0x, except

that:

Page 0 must be active.

Bytes/character is recalculated.

Max character rows is recalculated.

CRT buffer length is recalculated.

CRTC registers are reprogrammed as follows:

reg09h bytes/char-1; max scan line (mode 7 only)

reg0Ah bytes/char-2; cursor start

reg0Bh 0 ; cursor end

reg12h ((rows+1)*(bytes/char))-1

; vertical display end

reg14h bytes/char ; underline loc

(* BUG: should be 1 less *)

The following functions are meant to be called only

after a mode set:

20h user 8 by 8 graphics characters (int 1Fh)

ES:BP pointer to user table

21h user graphics characters

ES:BP pointer to user table

CX bytes per character

BL row specifier

0 user set

DL number of rows

1 14 rows

2 25 rows

3 43 rows

22h ROM 8 by 14 set

BL row specifier

23h ROM 8 by 8 double dot

BL row specifier

24h load 8x16 graphics characters (MCGA, VGA)

BL row specifier

30h Get Font Information (EGA, MCGA, VGA)

BH pointer specifier

0 int 1Fh pointer

1 int 44h pointer

2 ROM 8 by 14 character font pointer

3 ROM 8 by 8 double dot font pointer

4 ROM 8 by 8 DD font (top half)

5 ROM text alternate (9 by 14) pointer

return ES:BP specified pointer value

CX bytes/character

DL character rows on screen

Function 12h Alternate Select (EGA and after)

entry AH 12h

BL 10h return EGA information

return BH 00h if color mode is in effect (3Dx)

01h if mono mode is in effect (3Dx)

BL 00h if 64k EGA memory

01h if 128k EGA memory

02h if 192k EGA memory

03h if 256k EGA memory

CH feature bits

CL switch settings

20h select alternate print screen routine

30h select vertical resolution for text modes (VGA)

AL 00h 200 scan lines

01h 350 scan lines

02h 400 scan lines

return AL 12h if function supported

31h enable/disable default palette loading (MCGA, VGA)

AL 00h enable default palette loading

01h disable default palette loading

return AL 12h if function was supported

32h enable/disable video addressing (MCGA, VGA)

AL 00h enable video

01h disable video

return AL 12h if function was supported

33h enable/disable default gray scale summing (MCGA, VGA)

AL 00h enable gray scale summing

01h disable gray scale summing

return AL 12h if function was supported

34h enable/disable text cursor emulation (VGA)

AL 00h enable cursor emulation

01h disable cursor emulation

return AL 12h if function was supported

35h display-switch interface (PS/2)

AL 00h initial adapter video off

01h initial planar video on

02h switch active video off

03h switch inactive video on

80h *undocumented* set system board video

active flag

ES:DX buffer (128 byte save area if AL = 0, 2 or 3)

return AL 12h if function was supported

36h video refresh control (VGA)

AL 00h enable refresh

01h disable refresh

return AL 12h if function supported

BX 5500h (used by ATI and TAXAN)

BX 5502h (used by ATI and TAXAN)

Function 13h Enhanced String Write (AT, XT/286, PS/2)

entry AH 13h

AL 00h Write String, Don't Move Cursor

01h Write String, Move Cursor

02h Write String of Alternating Characters and Attributes;

Don't Move Cursor

bit 0: set in order to move cursor after write

bit 1: set if string contains alternating chars and

attributes

03h Write String of Alternating Characters and Attributes;

Move Cursor

bit 0: set in order to move cursor after write

bit 1: set if string contains alternating characters

and attributes

BH display page number

BL attribute if AL bit 1 clear

CX length of string

DH row of starting cursor position

DL column of starting cursor position

ES:BP pointer to start of string

return none

note Recognizes CR, LF, BS, and bell

Function 14h Load LCD Character Font (Convertible)

entry AH 14h

AL 00h load user specified font

BH number of bytes per character

BL 00h load main font (block 0)

01h load alternate font (block 1)

CX number of characters to store

DX character offset into RAM font area

ES:DI pointer to character font

AL 01h load system ROM default font

BL 00h load main font (block 0)

01h load alternate font (block 1)

AL 02h set mapping of LCD high intensity attribute

BL 00h ignore high intensity attribute

01h map high intensity to underscore

02h map high intensity to reverse video

03h map high intensity to seleected alternate font

return unknown

Function 15h Return Physical Display Parameters (Convertible)

entry AH 15h

return AX Alternate display adapter type

ES:DI pointer to parameter table:

word # information

01h monitor model number

02h vertical pixels per meter

03h horizontal pixels per meter

04h total number of vertical pixels

05h total number of horizontal pixels

06h horizontal pixel separation in micrometers

07h vertical pixel separation in micrometers

Function 1Ah Display Combination Code (MCGA, VGA)

Using the compatibility BIOS of the PS/2 Models 50, 60, 80 there

is a way to determine which video controller and attached

display are on the system. The Display Combination Code (DCC)

is a Video BIOS function that provides the capability.

entry AH 1Ah

AL 00h read display combination code

01h write display combination code

return AL 1Ah indicates Compatibility BIOS is supported,

any other value is invalid

BH Display Combination Code (DCC)

00h no display

01h IBM monochrome adapter and display

02h IBM color/graphics monitor adapter w/color display

03h reserved

04h IBM EGA, color display

05h IBM EGA, monochrome display

06h IBM PGA, color display

07h VGA, analog monochrome display

08h VGA, analog color display

09h reserved

0Ah MCGA, digital color display

0Bh MCGA, analog monochrome display

0Ch MCGA, analog color display

0FFh unknown display type

BL active display device code

note This function may be used to test for VGA, since it is not supported in

earlier adapters. If AL is still 1Ah when the call completes, a VGA

compatible adapter is present.

Function 1Bh Functionality/State Information (MCGA, VGA)

entry AH 1Bh

BX implementation type

0000h return funtionality/state information

ES:DI pointer to 64 byte buffer

return AL 1Bh if function supported

ES:DI buffer filled

00h address of functionality table

01h unknown

02h unknown

03h unknown

04h current video mode

05h number of columns

06h unknown

07h length of regen buffer in bytes

09h starting address of regen buffer

0Bh cursor position for page 0

0Dh cursor position for page 1

0Fh cursor position for page 2

11h cursor position for page 3

13h cursor position for page 4

15h cursor position for page 5

17h cursor position for page 6

19h cursor position for page 7

1Bh cursor type

1Dh active display page

1Eh CRTC port address

20h current setting of register (3?8)

21h current setting of register (3?9)

22h number of rows

23h bytes/character

25h DCC of active display

26h DCC of alternate display

27h number of colors supported in current mode

29h number of pages supported in current mode

2Ah number of scan lines active

(0,1,2,3) = (200,350,400,480)

2Bh primary character block

2Ch secondary character block

2Dh miscellaneous flags byte

bit 0 all modes on all displays on

1 gray summing on

2 monochrome display attached

3 default palette loading disabled

4 cursor emulation enabled

5 0=intensity; 1=blinking

6 reserved

7 reserved

2Eh to 30h reserved

31h video memory available

00h=64K, 01h=128K, 02h=192K, 03h=256K

32h save pointer state flags byte

bit 0 512 character set active

1 dynamic save area present

2 alphanumeric font override active

3 graphics font override active

4 palette override active

5 DCC override active

6 reserved

7 reserved

33h to 3Fh reserved

note State Functionality Table format (16 bytes)

00h modes supported #1

bit 0 to bit 7 = 1 modes 0,1,2,3,4,5,6 supported

01h modes supported #2

bit 0 to bit 7 = 1 modes 8,9,A,B,C,D,E,F supported

02h modes supported #3

bit 0 to bit 3 = 1 modes 10,11,12,13 supported

bit 4 to bit 7 reserved

03h to 06h reserved

07h scan lines supported

bit 0 to bit 2 = 1 if scan lines 200,350,400 supported

08h total number of character blocks available in text modes

09h maximum number of active character blocks in text modes

0Ah miscellaneous function flags #1

bit 0 all modes on all displays function supported

1 gray summing function supported

2 character font loading function supported

3 default palette loading enable/disable supported

4 cursor emulation function supported

5 EGA palette present

6 color palette present

7 color paging function supported

0Bh miscellaneous function flags #2

bit 0 light pen supported

1 save/restore state function 1Ch supported

2 intensity blinking function supported

3 Display Combination Code supported

4-7 reserved

0Ch to 0Dh reserved

0Eh Save pointer function flags

bit 0 512 character set supported

1 dynamic save area supported

2 text font override supported

3 graphics font override supported

4 palette override supported

5 DCC extension supported

6 reserved

7 reserved

0Fh reserved

Function 1Ch Save/Restore Video State (VGA)

entry AH 1Ch

AL 00h return state buffer size

01h save video state

ES:BX buffer address

02h restore video state

ES:BX buffer address of previously saved state

CX requested states

bit 0 video hardware

1 BIOS data areas

2 color registers and DAC state

3-15 reserved

return AL 1Ch if function supported

BX number of 64 byte blocks needed (function 00h)

note VGA only

Function 40h Set Graphics Mode (Hercules Graphics Card Plus)

entry AH 40h

return unknown

Function 41h Set Text Mode (Hercules Graphics Card Plus)

entry AH 41h

return unknown

Function 42h Clear Current Page (Hercules Graphics Card Plus)

entry AH 42h

return unknown

Function 43h Select Drawing Page (Hercules Graphics Card Plus)

entry AH 43h

AL page number (0,1)

return unknown

Function 44h Select Drawing Function (Hercules Graphics Card Plus)

entry AH 44h

AL 0 clear pixels

1 set pixels

2 invert pixels

return unknown

Function 45h Select Page to Display (Hercules Graphics Card Plus)

entry AH 45h

AL page number (0,1)

return unknown

Function 46h Draw One Pixel (Hercules Graphics Card Plus)

entry AH 46h

DI x (0-720)

BP y (0-347)

return unknown

note Function 44h determines operation and function 43h which page to use.

Function 47h Find Pixel Value (Hercules Graphics Card Plus)

entry AH 47h

DI x (0-720)

BP y (0-347)

return AL 0 pixel clear

1 pixel set

note Function 43h specifies page that is used.

Function 48h Move to Point (Hercules Graphics Card Plus)

entry AH 48h

DI x (0-720)

BP y (0-347)

return unknown

Function 49h Draw to Point (Hercules Graphics Card Plus)

entry AH 49h

DI x (0-720)

BP y (0-347)

return unknown

note Function 48h or 49h specify first point, 44h operation and 43h page

to use.

Function 4Ah Block Fill (Hercules Graphics Card Plus)

entry AH 4Ah

return unknown

Function 4Bh Display Character (Hercules Graphics Card Plus)

entry AH 4Bh

AL ASCII code for character to display

DI x (0-720)

BP y (0-347)

return unknown

note Unlike the other BIOS character functions character position is

specified in pixels rather than rows and columns.

Function 4Ch Draw Arc (Hercules Graphics Card Plus)

entry AH 4Ch

return unknown

Function 4Dh Draw Circle (Hercules Graphics Card Plus)

entry AH 4Dh

return unknown

Function 4Eh Fill Area (Hercules Graphics Card Plus)

entry AH 4Eh

return unknown

Function 6Ah Direct Graphics Interface Standard (DGIS)

entry AH 6Ah

AL 00h Inquire Available Devices

BX 0

CX 0

DX buffer length (may be 0)

ES:DI address of buffer

return BX number of bytes stored in buffer

CX bytes req'd for all descriptions (0 if no DGIS)

note Buffer contains descriptions and addresses of DGIS-

compatible display(s) and printer(s)

01h Redirect Character Output

CX 0

ES:DI address of device to send INT 10 output to

return CX 0 output could not be redirected

else INT 10h output now routed to requested display

02h Inquire int 10 Output Device

ES:DI 0:0

return ES:DI 0:0 if current display is non-DGIS

else address of the current DGIS INT 10 display

Function 6Fh Set Video Mode (VEGA Extended EGA/VGA)

entry AH 6F

AL 05h

BL mode| (graphics mode if graphics resolution listed)

62h 800x600 16 VEGA Extended EGA

65h 1024x768 16 VEGA Extended EGA

66h 640x400 256 VEGA Extended VGA

67h 640x480 256 VEGA Extended VGA

68h 720x540 256 VEGA Extended VGA

69h 800x600 256 VEGA Extended VGA

Function 70h Get Video RAM Address (Tandy 1000)

entry AH 70h

return AX segment addresses of the following

BX offset address of green plane

CX segment address of green plane

DX segment address of red/blue plane

note (red offset = 0, blue offset = 4000)

Function 71h Get INCRAM Addresses (Tandy 1000)

entry AH 71h

return AX segment address of the following

BX segment address of INCRAM

CX offset address of INCRAM

Function 72h Scroll Screen Right (Tandy 1000)

entry AH 72h

AL number of columns blanked at left of page

00h blank window

BH attributes to be used on blank columns

CH,CL row, column address of upper left corner

DH,DL row, column address of lower right corner

Function 73h Scroll Screen Left (Tandy 1000)

entry AH 73h

AL number of columns blanked at right of page

00h blank window

BH attributes to be used on blank columns

CH,CL row, column address of upper left corner

DH,DL row, column address of lower right corner

Function 80h DESQview - Set (something)

entry AH 80h

DX 4456h ('DV')

ES:DI pointer to FAR subroutine to be called on?

return DS segment of DESQview data structure for video buffer

note 1) This function is probably meant for internal use only, due to the magic

value required in DX

2) The subroutine seems to be called when the DESQview menu is accessed

on entry, AL = 03h or 04h

Function 81h DESQview video - Get something?

entry AH 81h

DX 4456h ('DV')

return ES segment of DESQview data structure for video buffer

byte ES:[0] = current window number

note This function is probably meant for internal use only, due to the

magic value required in DX

Function 82h DESQview - Get Current Window Info

entry AH 82h

DX 4456h ('DV')

return AH unknown

AL current window number

BH unknown

BL direct screen writes

0 program does not do direct writes

1 program does direct writes, so shadow buffer not usable

CH unknown

CL current video mode

DS segment in DESQview for data structure

in DV 2.00,

byte DS:[0] = window number

word DS:[1] = segment of other data structure

word DS:[3] = segment of window's object handle

ES segment of DESQview data structure for video buffer

note This function is probably meant for internal use only, due to the magic

value required in DX

Function 0F0h Microsoft Mouse driver EGA support - Read One Register

entry AX 0F0h

BL register number

DX group index

(pointer/data chips)

00h CRT Controller (25 reg) 3B4h mono, 3D4h color

08h sequencer (5 registers) 3C4h

10h graphics controller (9 registers) 3CEh

18h attribute controller (20 registers) 3C0h

(single registers)

20h miscellaneous output register 3C2h

28h feature control register (3BAh mono, 3DAh color

30h graphics 1 position register 3CCh

38h graphics 2 position register 3CAh

return BL data

Function 0F1h Microsoft Mouse driver EGA support - Write One Register

entry AX 0F1h

DX group index (see function F0h)

BL register number

BH value to write

return BL data

Function 0F2h Microsoft Mouse driver EGA support - Read Register Range

entry AX 0F2h

CH starting register number

CL number of registers (>1)

DX group index

00h CRTC (3B4h mono modes, 3D4h color modes)

08h sequencer 3C4h

10h graphics controller 3CEh

18h attribute controller 3C0h

ES:BX pointer to buffer, CL bytes

Function 0F3h Microsoft Mouse driver EGA support - Write Register Range

entry AX 0F3h

CH starting register

CL number of registers (>1)

DX group index

00h CRTC (3B4h mono modes, 3D4h color modes)

08h sequencer 3C4h

10h graphics controller 3CEh

18h attribute controller 3C0h

ES:BX pointer to buffer, CL bytes

Function 0F4h Microsoft Mouse driver EGA support - Read Register Set

entry AX 0F4h

CX number of registers (>1)

ES:BX pointer to table of records in this format:

bytes 1-2 group index

(pointer/data chips)

00h CRTC (3B4h mono modes, 3D4h color modes)

08h sequencer 3C4h

10h graphics controller 3CEh

18h attribute controller 3C0h

(single registers)

20h miscellaneous output register 3C2h

28h feature control register (3BAh mono modes, 3DAh color)

30h graphics 1 position register 3CCh

38h graphics 2 position register 3CAh

byte 3 register number (0 for single registers)

byte 4 register value

Function 0F5h Microsoft Mouse driver EGA support - Read Register Set

entry AX 0F5h

CX number of registers (>1)

ES:BX pointer to table of records in this format:

bytes 1-2 group index

(pointer/data chips)

00h CRTC (3B4h mono modes, 3D4h color modes)

08h sequencer 3C4h

10h graphics controller 3CEh

18h attribute controller 3C0h

(single registers)

20h miscellaneous output register 3C2h

28h feature control register (3BAh mono modes, 3DAh color)

30h graphics 1 position register 3CCh

38h graphics 2 position register 3CAh

byte 3 register number (0 for single registers)

byte 4 register value

Function 0F6h Microsoft Mouse driver EGA support

Revert to Default Registers

entry AX 0F6h

return unknown

Function 0F7h Microsoft Mouse driver EGA support

Define Default Register Table

entry AX 0F7h

DX port number

ES:BX address of table of one byte entries, one byte to be written to

each register

(pointer/data chips)

00h CRTC (3B4h mono modes, 3D4h color modes)

08h sequencer 3C4h

10h graphics controller 3CEh

18h attribute controller 3C0h

(single registers)

20h miscellaneous output register 3C2h

28h feature control register (3BAh mono, 3DAh color)

30h graphics 1 position register 3CCh

38h graphics 2 position register 3CAh

Function 0FAh Microsoft Mouse driver EGA support - Interrogate Driver

entry AX 0FAh

BX 00h

return BX 00h if mouse driver not present

ES:BX pointer to EGA Register Interface version number, if present:

byte 1 major release number

byte 2 minor release number

Function 0FEh Get Alternate Screen Buffer Address (text mode only)

(Topview/DesQview/Taskview)

entry AH 0FEh

ES:DI segment:offset of assumed video buffer

return: ES:DI segment:offset of actual video buffer

note 1) This alternate video buffer can be written to directly, in the same

manner as writing to B:000 or B:800. The MT program will manage the

actual display.

2) There is no need to synchronize vertical retrace when writing to the

alternate buffer; this is managed by the MT program

3) If TopView or DESQview is not running, ES:DI is returned unchanged.

4) TopView requires that function 0FFh be called every time you write into

the buffer to tell TopView that something changed

Function 0FFh Update Real Display (text mode only) (TopView)

Update Video Buffer (Topview/DesQview/Taskview)

entry AH 0FFh

CX number of sequential characters that have been modified

DI offset of first character that has been modified

ES segment of video buffer

return unknown

note 1) DesQview supports this call, but does not require it

2) Avoid CX=0

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³Interrupt 11h Equipment Check ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0044h) fetch a code describing active peripherals.

entry AH 11h

return AX Equipment listing word Bits are:

0 number of floppy drives

0 no drives

1 bootable (IPL) diskette drive installed

1 math chip

0 no math coprocessor (80x87) present

1 math coprocessor (80x87) present

(PS/2) 2 0 mouse not installed

1 mouse installed

(PC) 2,3 system board RAM

0,0 16k (PC-0, PC-1)

1,1 64k (PC-2, XT)

note 1) not commonly used. Set both bits to 1

2) both bits always 1 in AT

4,5 initial video mode

0,0 no video installed (use with dumb terminal)

0,1 40x25 color (CGA)

1,0 80x25 color (CGA, EGA, PGA, MCGA, VGA)

1,1 80x25 monochrome (MDA or Hercules, most super-

hires mono systems)

6,7 number of diskette drives (only if bit 0 1)

0,0 1 drives

0,1 2 drives

1,0 3 drives

1,1 4 drives

8 0 DMA present

1 no DMA (PCjr, some Tandy 1000s, 1400LT)

9,A,B number of RS232 serial ports (0-3)

0,0,0 none

0,0,1 1

0,1,0 2

0,1,1 3

1,0,0 4

C 0 no game I/O attached

1 game I/O attached (default for PCjr)

D serial accessory installation

0 no serial accessories installed

1 Convertible - internal modem installed

1 PCjr - serial printer attached

E,F number of parallel printers

0,0 none

0,1 one (LPT1, PRN)

1,0 two (LPT2)

1,1 three (LPT3)

note Models before PS/2 would allow a fourth

parallel printer. Remapping of the BIOS in the

PS/2s does not allow the use of LPT4.

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³Interrupt 12h Memory Size ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0048h) get system memory

return AX number of contiguous 1K RAM blocks

note 1) This service does not depend on the setting of the motherboard switches

2) This is the same value stored in absolute address 04:13h

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³Interrupt 13h Disk I/O - access the disk drives (floppy and hard disk) ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:004Ch) does not try rereading disk if an error is returned

Function 00h Reset - reset the disk controller chip

entry AH 00h

DL drive (if bit 7 is set both hard disks and floppy disks reset)

return AH status

note 1) Forces controller chip to recalibrate read/write heads

2) Some systems (Sanyo 55x) this resets all drives

Function 01h Get Status of disk system

entry AH 01h

DL drive (hard disk if bit 7 set)

return AL status of most recent operation

00h successful completion

01h bad command

02h address mark not found

03h tried to write on write-protected disk

04h sector not found

05h reset failed (hard disk)

06h diskette removed or changed

07h bad parameter table (hard disk)

08h DMA overrun

09h attempt to DMA across 64K boundary

0Ah bad sector detected (hard disk)

0Bh bad track detected (hard disk)

0Ch unsupported track

0Dh invalid number of sectors on format (hard disk)

0Eh control data address mark detected (hard disk)

0Fh DMA arbitration error (hard disk)

10h bad CRC/EEC on read

11h data ECC corrected

20h controller failure

40h seek failed

80h timeout

0AAh drive not ready (hard disk)

0BBh undefined error (hard disk)

0CCh write fault (hard disk)

0E0h status error (hard disk)

0FFh sense operation failed (hard disk)

Function 02h Read Sectors - read one or more sectors from diskette

entry AH 02h

AL number of sectors to read

BX address of buffer (ES=segment)

CH track number (0-39 or 0-79 for floppies)

(for hard disk, bits 8,9 in high bits of CL)

CL sector number (1 to 18, not value checked)

DH head number (0 or 1)

DL drive (0=A, 1=B, etc.) (bit 7=0) (drive 0-7)

ES:BX address to store/fetch data (buffer to fill)

[0000:0078] dword pointer to diskette parms

return CF clear (0) for successful

set (1) failure

AH status (00h, 02h, 03h, 04h, 08h, 09h, 10h, 0Ah, 20h,

40h, 80h)

AL number of sectors transferred

note 1) Number of sectors begins with 1, not 0

2) Trying to read zero sectors is considered a programming error; results

are not defined

Function 03h Write Sectors - write from memory to disk

entry AH 03h

AL number of sectors to write (1-8)

CH track number (for hard disk, bits 8,9 in high bits of CL)

CL beginning sector number

(if hard disk, high two bits are high bits of track #)

DH head number

DL drive number (0-7)

ES:BX address of buffer for data

return CF set if error

AH status (see above)

AL number of sectors written

note 1) Number of sectors begins with 1, not 0

2) Trying to write zero sectors is considered a programming error; results

are not defined

Function 04h Verify - verify that a write operation was successful

entry AH 04h

AL number of sectors to verify (1-8)

CH track number (for hard disk, bits 8,9 in high bits of CL)

CL beginning sector number

DH head number

DL drive number (0-7)

return CF set on error

AH status (see above)

AL number of sectors verified

Function 05h Format Track - write sector ID bytes for 1 track

entry AH 05h

AL number of sectors to create on this track

CH track (or cylinder) number

CL sector number

DH head number (0, 1)

DL drive number (0-3)

ES:BX pointer to 4-byte address field (C-H-R-N)

byte 1 = (C) cylinder or track

byte 2 = (H) head

byte 3 = (R) sector

byte 4 = (N) bytes/sector (0 = 128, 1 = 256, 2 = 512, 3 = 1024)

return CF set if error occurred

AH status code (see above)

note Not valid for ESDI hard disks on PS/2

Function 06h Hard Disk - format track and set bad sector flags

(PC2, PC-XT, and Portable)

entry AH 06h

AL interleave value (XT only)

CH cylinder number (bits 8,9 in high bits of CL)

CL sector number

DH head

DL drive

ES:BX 512 byte format buffer

the first 2*(sectors/track) bytes contain f,n for each sector

f 00Fh for good sector

80h for bad sector

n sector number

return AH status code

Function 07h Hard Disk - format the drive starting at the desired track

(PC2, PC-XT and Portable)

entry AH 07h

AL interleave value (XT only) (01h-10h)

CH cylinder number (bits 8,9 in high bits of CL) (00h-03FFh)

CL sector number

DH head number (0-7)

DL drive number (80h-87h, 80h=C, 81h=D,...)

ES:BX format buffer, size = 512 bytes

the first 2*(sectors/track) bytes contain f,n for each sector

f=00h for good sector

80h for bad sector

n=sector number

return AH status code (see above)

note Award AT BIOS routines are extended to handle more than 1024 cylinders.

AL number of sectors

CH cylinder numberm low 8 bits

CL sector number bits 0-5, bits 6-7 are high 2 cylinder bits

DH head number (bits 0-5) bits 6-7 are extended high cyls (>1024)

DL drive number (0-1 for diskette, 80h-81h for hard disk)

ES:BX transfer address

Function 08h Read Drive Parameters (XT, CONV, AT, XT/286, PS/2)

entry AH 08h

DL drive number (0-2)

return CF set on error

AH status code (see above)

BL drive type (see AH=17h below) (AT/PS2 floppies only)

CH maximum useable value for cylinder number

CL maximum useable value for sector number or cylinder number

DH maximum usable value for head number

DL number of consecutive acknowledging drives (0-2)

ES:DI drive parameter table

Function 09h Initialize Two Fixed Disk Base Tables (XT, AT, XT/286, PS/2)

(install nonstandard drive)

entry AH 09h

return CF set on error

AH status code (see above)

data block definitions:

+0 maximum number of cylinders (dw)

+2 maximum number of heads (db)

+3 starting reduced write current cylinder (dw - XT only)

+5 starting write precomp cylinder (dw)

+7 maximum ECC data burst length (db - XT only)

+8 control byte: Bits

0,1,2 Ä drive option

3,4,5 - always zero

6 - disable ECC retries

7 - disable access retries

note 1) Int 41h points to table for drive 0

2) Int 46h points to table for drive 1

3) 41h used by XT, 41h and 46h used by AT

Function 0Ah Read Long (Hard disk) (XT, AT, XT/286, PS/2)

entry AH 0Ah

CH cylinder number (bits 8,9 in high bits of CL)

CL sector number

DL drive ID

DH head number

ES:BX pointer to buffer to fill

return CF set on error

AH status code (see above)

AL number of sectors actually transferred

note 1) A "long" sector includes a 4 byte EEC (Extended Error Correction) code

2) Used for diagnostics only on PS/2 systems

Function 0Bh Write Long (XT, AT, XT/286, PS/2)

entry AH 0Bh

CH cylinder (bits 8,9 in high bits of CL)

CL sector number

DH head number

DL drive ID

ES:BX pointer to buffer containing data

return CF set on error

AH status code (see above)

AL number of sectors actually transferred

note 1) A "long" sector includes a 4 byte EEC (Extended Error Correction) code

2) Used for diagnostics only on PS/2 systems

Function 0Ch Seek To Cylinder (except PC, PCjr)

entry AH 0Ch

CH cylinder number (bits 8,9 in high bits of CL)

DH head number

DL drive ID

return CF set on error

AH status code (see above)

note 1) Positions heads over a particular cylinder

Function 0Dh Alternate Disk Reset (except PC, PCjr)

entry AH 0Dh

DL drive ID

return CF set on error

AH status code (see above)

note Not for PS/2 ESDI hard disks

Function 0Eh Read Sector Buffer (XT, Portable PS/2)

entry AH 0Eh

AL number of sectors

CH cylinder (bits 8,9 in top two bits of CL)

CL sector number

DH head number

DL drive number

ES:BX pointer to buffer

return CF set on error

AH status code (see above)

AL number of sectors actually transferred

note 1) Transfers controller's sector buffer. No data is read from the drive

2) Used for diagnostics only on PS/2 systems

Function 0Fh Write sector buffer (XT, Portable)

entry AH 0Fh

AL number of sectors

CH cylinder (bits 8,9 in top two bits of CL)

CL sector number

DH head number

DL drive number

ES:BX pointer to buffer

return CF set if error

AH status code

AL number of sectors actually transferred

note 1) Should be called before formatting to initialize the controller's

sector buffer.

2) Used for diagnostics only on PS/2 systems

Function 10h Test For Drive Ready

entry AH 10h

DL drive ID

return CF set on error

AH status code (see above)

Function 11h Recalibrate Drive

entry AH 11h

DL drive ID

return CF set on error

AH status code (see above)

Function 12h Controller RAM Diagnostic (XT, Portable, PS/2)

entry AH 12h

return CF set on error

AH status code (see AH=1 above)

note Used for diagnostics only on PS/2 systems

Function 13h Drive Diagnostic (XT, Portable)

entry AH 13h

return CF set on error

AH status code (see above)

note Used for diagnostics only on PS/2 systems

Function 14h Controller Internal Diagnostic (AT, XT/286)

entry AH 14h

return CF set on error

AH status code (see above)

note 1) OEM is Western Digital 1003-WA2 hard/floppy combination controller

in AT and XT/286.

2) Used for diagnostics only in PS/2 systems

Function 15h Get Disk Type (except PC and XT)

entry AH 15h

DL drive ID

return AH disk type

00h no drive is present

01h diskette, no change detection present

02h diskette, change detection present

03h fixed disk

CX:DX number of 512-byte sectors when AH = 03h

Function 16h Change of Disk Status (diskette) (except PC and XT)

entry AH 16h

return AH disk change status

00h no disk change

01h disk changed

DL drive that had disk change

Function 17h Set Disk Type for Format (diskette) (except PC and XT)

entry AH 17h

AL 00h no disk

01h 360kb diskette in 360Kb drive

02h 360kb diskette in 1.2M drive

03h 1.2M diskette in 1.2M drive

04h 720kb diskette in 720Kb drive

DL drive number

return AH status of operation

note This function is probably enhanced for the PS/2 series to detect

1.44 in 1.44 and 720k in 1.44.

Function 18h Set Media Type For Format (diskette) (AT, XT/286, PS/2)

entry AH 18h

CH lower 8 bits of number of tracks

CL high 2 bits of number of tracks (6,7) sectors per track

(bits 0-5)

DL drive number

return AH 00h if requested combination supported

01h if function not available

0Ch if not suppported or drive type unknown

80h if there is no media in the drive

ES:DI pointer to 11-byte parameter table

Function 19h Park Hard Disk Heads (XT/286, PS/2)

entry AH 19h

DL drive

return CF set on error

AH error code

Function 1Ah ESDI Hard Disk - Format (PS/2)

entry AH 1Ah

AL defect table count

CL format modifiers

bits 0 ignore primary defect map

1 ignore secondary defect map

2 update secondary defect map

3 perform surface analysis

4 generate periodic interrupt

DL drive

ES:BX pointer to defect table

return CF set on error

AH status (see AH=1 above)

note If periodic interrupt selected, int 15h/AH=0Fh is called after each

cylinder is formatted

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 14h Initialize and Access Serial Port For Int 14 ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0050h) the following status is defined:

serial status byte:

bits 0 delta clear to send

1 delta data set ready

2 trailing edge ring detector

3 delta receive line signal detect

4 clear to send

5 data set ready

6 ring indicator

7 receive line signal detect

line status byte:

bits 0 data ready

1 overrun error

2 parity error

3 framing error

4 break detect

5 transmit holding register empty

6 transmit shift register empty

7 time out note: if bit 7 set then other bits are invalid

All routines have AH=function number and DX=RS232 card number (0 based).

AL=character to send or received character on exit, unless otherwise noted.

entry AH 00h Initialize And Access Serial Communications Port

bit pattern: BBBPPSLL

BBB = baud rate: 110,150,300,600,1200,2400,4800,9600

PP = parity: 01 = odd, 11 = even

S = stop bits: 0 = 1, 1 = 2

LL = word length: 10 = 7-bits, 11 = 8-bits

AL parms for initialization:

bit pattern:

0 word length

1 word length

2 stop bits

3 parity

4 parity

5 baud rate

6 baud rate

7 baud rate

word length 10 7 bits

11 8 bits

stop bits 0 1 stop bit

1 2 stop bits

parity 00 none

01 odd

11 even

baud rate 000 110 baud

001 150 baud

010 300 baud

011 600 baud

100 1200 baud

101 2400 baud

110 4800 baud

111 9600 baud (4800 on PCjr)

DX port number

return AH line status

AL modem status

Function 01h Send Character in AL to Comm Port DX (0 or 1)

entry AH 01h

AL character

DX port number (0 or 1)

return AH RS232 status code

bit 0 data ready

1 overrun error

2 parity error

3 framing error

4 break detected

5 transmission buffer register empty

6 transmission shift register empty

7 timeout

AL modem status

bit

0 delta clear-to-send

1 delta data-set-ready

2 trailing edge ring detected

3 change, receive line signal detected

4 clear-to-send

5 data-set-ready

6 ring received

7 receive line signal detected

Function 02h Wait For A Character From Comm Port DX

entry AH 02h

return AL character received

AH error code (see above)(00h for no error)

Function 03h Fetch the Status of Comm Port DX (0 or 1)

entry AH 03h

return AH set bits (01h) indicate comm-line status

bit 7 timeout

bit 6 empty transmit shift register

bit 5 empty transmit holding register

bit 4 break detected ("long-space")

bit 3 framing error

bit 2 parity error

bit 1 overrun error

bit 0 data ready

AL set bits indicate modem status

bit 7 received line signal detect

bit 6 ring indicator

bit 5 data set ready

bit 4 clear to send

bit 3 delta receive line signal detect

bit 2 trailing edge ring detector

bit 1 delta data set ready

bit 0 delta clear to send

Function 04h Extended Initialize (PC Convertible)

entry AH 04h

AL break status

01h if break

00h if no break

BH parity

00h no parity

01h odd parity

02h even parity

03h stick parity odd

04h stick parity even

BL number of stop bits

00h one stop bit

01h 2 stop bits (1« if 5 bit word length)

CH word length

00h 5 bits

01h 6 bits

02h 7 bits

03h 8 bits

CL baud rate

00h 110

01h 150

02h 300

03h 600

04h 1200

05h 2400

06h 4800

07h 9600

08h 19200

return AL modem status

AH line control status

Function 05h Extended Communication Port Control (PS/2)

entry AH 05h

AL 00h read modem control register

return BL modem control reg (see AL=1)

AL 01h write modem control register

BL modem control register: (for AL=00 and AL=01) bits

0 data terminal ready

1 request to send

2 out1

3 out2

4 loop

5,6,7 reserved

return AH status

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 15h Cassette I/O ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0054h) Renamed "System Services" on PS/2 line

Function 00h Turn Cassette Motor On (PC, PCjr only)

entry AH 00h

return AH 86h no cassette present

CF set on error

AH error code

00h no errors

01h CRC error

02h bad tape signals

no data transitions (PCjr)

03h no data found on tape

not used (PCjr)

04h no data

no leader (PCjr)

80h invalid command

86h no cassette present

not valid in PCjr

note NOP for systems where cassette not supported

Function 01h Turn Cassette Motor Off (PC, PCjr only)

entry AH 01h

return AH 86h no cassette present

CF set on error

AH error code

note NOP for systems where cassette not supported

Function 02h Read Blocks From Cassette (PC, PCjr only)

entry AH 02h

CX count of bytes to read

ES:BX pointer to data buffer

return CF set on error

AH error code

DX count of bytes actually read

ES:BX pointer past last byte written

note 1) NOP for systems where cassette not supported

2) Cassette operations normally read 256 byte blocks

Function 03h Write Data Blocks to Cassette (PC, PCjr only)

entry AH 03h

CX count of bytes to write

ES:BX pointer to data buffer

return CF set on error

AH error code (see 02h)

CX 0

ES:BX pointer to last byte written+1

note 1) NOP for systems where cassette not supported

2) The last block is padded to 256 bytes with zeroes if needed

3) No errors are returned by this service

Function 0Fh ESDI Format Unit Periodic Interrupt (PS/2 50, 60, 80)

entry AH 0Fh

AL phase code

00h reserved

01h surface analysis

02h formatting

return CF clear if formatting should continue

set if it should terminate

note Called during ESDI drive formatting after each cylinder is completed

Function 10h TopView API Function Calls (TopView)

entry AH 00h PAUSE Give Up CPU Time

return 00h after other processes run

01h GETMEM allocate "system" memory

BX number of bytes to allocate

return ES:DI pointer to block of memory

02h PUTMEM deallocate "system" memory

ES:DI pointer to previously allocated block

return block freed

03h PRINTC display character/attribute on screen

BH attribute

BL character

DX segment of object handle for window

note BX=0 does not display anything, it only

positions the hardware cursor

10h unknown

AL 04h thru 12h

return TopView - unimplemented in DV 2.0x

pops up "Programming error" window in DV 2.0x

11h unknown

12h unknown

13h GETBIT define a 2nd-level interrupt handler

ES:DI pointer to FAR service routine

return BX bit mask indicating which bit was

allocated

0 if no more bits available

14h FREEBIT undefine a 2nd-level interrupt handler

BX bit mask from int 15/AH 13h

15h SETBIT schedule one or more 2nd-level interrupts

BX bit mask for interrupts to post

return indicated routines will be called at next ???

16h ISOBJ verify object handle

ES:DI possible object handle

return BX -1 if ES:DI is a valid object handle

0 if ES:DI is not

17h TopView - unimplemented in DV 2.00

return pops up "Programming Error" window in DV 2.00

18h LOCATE Find Window at a Given Screen Location

BH column

BL row

ES segment of object handle for ?

(0 = use default)

return ES segment of object handle for window

which is visible at the indicated

position

19h SOUND Make Tone

BX frequency in Hertz

CX duration in clock ticks (18.2 ticks/sec)

return immediately, tone continues to completion

note If another tone is already playing, the new tone

does not start until completion of the previous

one. In DV 2.00, it is possible to enqueue

about 32 tones before the process is blocked

until a note completes.

In DV 2.00, the lowest tone allowed is 20 Hz

1Ah OSTACK Switch to Task's Internal Stack

return stack switched

1Bh BEGINC Begin Critical Region

return task-switching temporarily disabled

note Will not task-switch until END CRITICAL REGION

(AH=1Ch) is called

1Ch ENDC End Critical Region

return task-switching enabled

1Dh STOP STOP TASK

ES segment of object handle for task to be stopped

(= handle of main window for that task)

return indicated task will no longer get CPU time

note At least in DV 2.00, this function is ignored

unless the indicated task is the current task.

1Eh START Start Task

ES segment of object handle for task to be started

(== handle of main window for that task)

return Indicated task is started up again

1Fh DISPEROR Pop-Up Error Window

BX bit fields:

0-12 number of characters to display

13,14 which mouse button may be pressed to

remove window

00 either

01 left

10 right

11 either

15 beep if 1

DS:DI pointer to text of message

CH width of error window (0 = default)

CL height of error window (0 = default)

DX segment of object handle

return BX status:

1 left button pressed

2 right button pressed

27 ESC key pressed

note Window remains on-screen until ESC or indicated

mouse button is pressed

20h TopView - unimplemented in DV 2.0x

return pops up "Programming Error" window in DV 2.0x

21h PGMINT Interrupt Another Task

BX segment of object handle for task to interrupt

DX:CX address of FAR routine to jump to next time

task is run

return nothing?

note The current ES, DS, SI, DI, and BP are passed

to the FAR routine

22h GETVER Get Version

BX 00h

return BX nonzero, TopView or compatible loaded

BH minor version

BL major version

notes TaskView returns BX = 0001h

DESQview 2.0 returns BX = 0A01h

23h POSWIN Position Window

BX segment of object handle for parent window

within which to position the window (0 = full

screen)

CH # columns to offset from position in DL

CL # rows to offset from position in DL

DL bit flags

0,1 horizontal position

00 current

01 center

10 left

11 right

2,3 vertical position

00 current

01 center

10 top

11 bottom

4 don't redraw screen if set

5-7 not used

ES segment of object handle for window to be

positioned

return nothing

24h GETBUF Get Virtual Screen Information

BX segment of object handle for window (0=default)

return CX size of virtual screen in bytes

DL 0 or 1, unknown

ES:DI address of virtual screen

25h USTACK Switch Back to User's Stack

return stack switched back

note Call only after int 15h,fn1Ah

26h-2Ah DesQview (TopView?) - unimplemented in DV 2.0x

return pops up "Programming Error" window in DV 2.0x

2Bh POSTTASK Awaken Task DesQview 2.0 (TopView?)

BX segment of object handle for task

return nothing

2Ch Start New Application in New Process

DesQview 2.0 (TopView?)

ES:DI pointer to contents of .PIF/.DVP file

BX size of .PIF/.DVP info

return BX segment of object handle for new task

2Dh Keyboard Mouse Control DesQview 2.0

BL subfunction

00h determine whether using keyboard mouse

01h turn keyboard mouse on

02h turn keyboard mouse off

return (calling BL was 00h)

BL 0 using real mouse

1 using keyboard mouse

Function 11h Topview commands

entry AH 11h

AL various

note In DesQview 2.0x, these function calls are identical to AH=0DEh, so

see those below

Function 20h PRINT.COM (DOS internal) (AT, XT-286, PS/2 50+)

entry AH 20h

AL subfunction

00h unknown (PRINT)

01h unknown (PRINT)

10h sets up SysReq routine on AT, XT/286, PS/2

11h completion of SysReq routine (software only)

note 1) AL=0 or 1 sets or resets some flags which affect what PRINT does when

it tries to access the disk

Function 21h Power-On Self Test (POST) Error Log (PS/2 50+)

entry AH 21h

AL 00h read POST log

01h write POST log

BH device ID

BL error code

return CF set on error

AH status

00h OK

BX number of error codes stored

ES:DI pointer to error log

01h list full

80h invalid command

86h unsupported

note The log is a series of words, the first byte of which identifies the

error code and the second the device.

Function 40h Read/Modify Profiles (Convertible)

entry AH 40h

AL 00h read system profile in CX,BX

01h write system profile from CX, BX

02h read internal modem profile in BX

03h write internal modem profile from BX

BX profile info

return BX internal modem profile (from 02h)

CX,BX system profile (from 00h)

Function 41h Wait On External Event (Convertible)

entry AH 41h

AL condition type

bits 0-2: condition to wait for

0 any external event

1 compare and return if equal

2 compare and return if not equal

3 test and return if not zero

4 test and return if zero

bit 3: reserved

bit 4: 1=port address, 0=user byte

bits 5-7: reserved

BH condition compare or mask value

condition codes:

0 any external event

1 compare and return if equal

2 compare and return if not equal

3 test and return if not zero

4 test and return if zero

BL timeout value times 55 milliseconds

0 if no time limit

DX I/O port address (if AL bit 4 = 1)

ES:DI pointer to user byte (if AL bit 4 = 0)

Function 42h Request System Power Off (Convertible)

entry AH 42h

AL 00h to use system profile

01h to force suspend regardless of profile

Function 43h Read System Status (Convertible)

entry AH 43h

return AL status bits:

0 LCD detached

1 reserved

2 RS232/parallel powered on

3 internal modem powered on

4 power activated by alarm

5 standby power lost

6 external power in use

7 battery low

Function 44h (De)activate Internal Modem Power (Convertible)

entry AH 44h

AL 00h to power off

01h to power on

Function 4Fh Keyboard Intercept (except PC, PCjr, and XT)

entry AH 4Fh

AL scan code, CF set

return AL scan code, CF set if processing desired

note Called by int 9 handler to translate scan codes

Function 80h Device Open (AT, XT/286, PS/2)

entry AH 80h

BX device ID

CX process ID

return CF set on error

AH status

Function 81h Device Close (AT, XT/286, PS/2)

entry AH 81h

BX device ID

CX process ID

return CF set on error

AH status

Function 82h Program Termination (AT, XT/286, PS/2)

AH 82h

BX device ID

return: CF set on error

AH status

note Closes all devices opened with function 80h

Function 83h Event Wait (AT, XT/286, Convertible, PS/2)

entry AH 83h

AL 00h to set interval

10h to cancel

CX,DX number of microseconds to wait (granularity is 976 microseconds)

ES:BX pointer to memory flag (bit 7 is set when interval expires)

(pointer is to caller's memory)

return CF set (1) if function already busy

Function 84h Read Joystick Input Settings (AT, XT/286, PS/2)

entry AH 84h

DX 00h to read the current switch settings (return in AL)

01h to read the resistive inputs

return AX A(X) value

BX A(Y) value

CX B(X) value

DX B(Y) value

AL switch settings (bits 7-4)

Function 85h System Request (SysReq) Key Pressed (except PC, PCjr, XT)

entry AH 85h

return AL 00h key pressed

01h key released

note Called by keyboard decode routine

Function 86h Elapsed Time Wait (except PC, PCjr, XT)

AH 86h

CX,DX number of microseconds to wait

return CF clear after wait elapses

CF set immediately due to error

note Only accurate to 977 microseconds

Function 87h Extended Memory Block Move (286/386 machines only)

AH 87h

CX number of words to move

ES:SI pointer to Global Descriptor Table (GDT)

offset 00h null descriptor

08h uninitialized, will be made into GDT descriptor

10h descriptor for source of move

18h descriptor for destination of move

20h uninitialized, used by BIOS

28h uninitialized, will be made into SS descriptor

return CF set on error

AH status

00h source copied into destination

01h parity error

02h interrupt error

03h address line 20 gating failed

Function 88h Extended Memory Size Determine (AT, XT/286, PS/2)

entry AH 88h

return AX # of contiguous 1K blocks of memory starting at address 1024k

Function 89h Switch Processor to Protected Mode (AT, XT/286, PS/2)

entry AH 89h

BH interrupt number of IRQ 8 (IRQ 9Fh use next 7 interrupts)

BL interrupt number of IRQ 0 (IRQ 17h use next 7 interrupts)

CX offset into protected mode CS to jump to

DS:SI pointer to Global Descriptor Table for protected mode

offset 00h null descriptor

08h GDT descriptor

10h IDT descriptor

18h DS

20h ES

28h SS

30h CS

38h uninitialized, used to build descriptor for

BIOS CS

return AH 0FFh error enabling address line 20

CF set on error

Function 90h Device Busy Loop (except PC, PCjr, XT)

entry AH 90h

AL type code:

00h disk

01h diskette

02h keyboard

03h PS/2 pointing device

80h network (ES:BX = pointer to network control block)

0FCh hard disk reset (PS/2)

0FDh diskette motor start

0FEh printer

ES:BX pointer to request block for type codes 80h through 0BFh

return CF 1 (set) if wait time satisfied

0 (clear) if driver must perform wait

note Used by NETBIOS

Type codes are allocated as follows:

00h-7Fh non-reentrant devices; OS must arbitrate access

80h-BFh reentrant devices; ES:BX points to a unique control block

C0h-FFh wait-only calls, no complementary int 15, fn91h call

Function 91h Set Flag and Complete Interrupt (except PC, PCjr, XT)

entry AH 91h

AL type code (see AH=90h above)

ES:BX pointer to request block for type codes 80h through 0BFh

return AH 0

note Used by NETBIOS

Function 0C0h Get System Configuration (XT after 1/10/86, PC Convertible,

XT/286, AT, PS/2)

entry AH 0C0h

return CF 1 if BIOS doesn't support call

ES:BX pointer to ROM system descriptor table

dword number of bytes in the following table (norm. 16 bytes)

byte system ID byte; see Chapter 2 for interpretation

byte secondary ID distingushes between AT and XT/286, etc.

byte BIOS revision level, 0 for 1st release, 1 for 2nd, etc.

byte feature information

80h DMA channel 3 used by hard disk BIOS

40h 2nd 8259 installed

20h realtime clock installed

10h int 15h, fn 04h called upon int 09h

08h wait for external event supported (int 15fn41)

used on Convertible; reserved on PS/2 systems

04h extended BIOS area allocated at 640k

03h reserved

02h bus is Micro Channel instead of PC

01h reserved

00h reserved

byte unknown (set to 0) (reserved by IBM)

byte unknown (set to 0)

byte unknown (set to 0) (Award copyright here)

note 1) Int 15h is also used for the Multitask Hook on PS/2 machines. No

2) The 1/10/86 XT BIOS returns an incorrect value for the feature byte.

Function 0C1h System - Return Extended-BIOS Data-Area Segment Address (PS/2)

entry AH 0C1h

return CF set on error

ES segment of data area

Function 0C2h Pointing Device BIOS Interface (DesQview 2.x) (PS/2)

entry AH 0C2h

AL 00h enable/disable

BH 00h disable

01h reset

return BH device ID

02h set sampling rate

BH 00h 10/second

01h 20/second

02h 40/second

03h 60/second

04h 80/second

05h 100/second

06h 200/second

03h set resolution

BH 00h one count per mm

01h two counts per mm

02h four counts per mm

03h eight counts per mm

04h get type

return BH device ID

05h initialize

BH data package size (1 - 8 bytes)

06h get/set scaling factor

BH 00h return device status

return BL status byte

bit 0: right button pressed

bit 1: reserved

bit 2: left button pressed

bit 3: reserved

bit 4: 0=1:1 scaling, 1=2:1 scaling

bit 5: device enabled

bit 6: 0=stream mode, 1=remote mode

bit 7: reserved

CL resolution (see function 03h)

DL sample rate, reports per second

01h set scaling at 1:1

02h set scaling at 2:1

07h set device handler address

ES:BX user device handler

return AL 00h

return CF set on error

AH status

00h successful

01h invalid function

02h invalid input

03h interface error

04h need to resend

05h no device handler installed

note The values in BH for those functions that take it as input are stored

in different locations for each subfunction

Function 0C3h Enable/Disable Watchdog Timeout (PS/2 50+)

entry AH 0C3h

AL 00h disable

01h enable

BX timer counter

return CF set on error

note The watchdog timer generates an NMI

Function 0C4h Programmable Option Select (PS/2 50+)

entry AH 04Ch

AL 00h return base POS register address

01h enable slot

BL slot number

02h enable adapter

return CF set on error

DX base POS register address (if function 00h)

Function 0DEh DesQview Services (DesQview)

entry AH 0DEh

AL 00h Get Program Name

return AX offset into DESQVIEW.DVO of current

program's record:

byte length of name

n bytes name

2 bytes keys to invoke program (second

= 00h if only one key used)

word ? (I see 0 always)

byte end flag: 00h for all but last

entry, which is 0FFh

01h Update "Open Window" Menu

return none

note Reads DESQVIEW.DVO, disables Open menu if file

not in current directory

02h unimplemented in DV 2.0x

return nothing (NOP in DV 2.0x)

03h unimplemented in DV 2.0x

return nothing (NOP in DV 2.0x)

04h Get Available Common Memory

return BX bytes of common memory available

CX largest block available

DX total common memory in bytes

05h Get Available Conventional Memory

return BX K of memory available

CX largest block available

DX total conventional memory in K

06h Get Available Expanded Memory

return BX K of expanded memory available

CX largest block available

DX total expanded memory in K

07h APPNUM Get Current Program's Number

return AX number of program as it appears on the

"Switch Windows" menu

08h GET (unknown)

return AX 0 unknown

1 unknown

09h unimplemented in DV 2.00

return nothing (NOP in DV 2.00)

0Ah DBGPOKE Display Character on Status Line

BL character

return character displayed, next call will display in

next position (which wraps back to the start of

the line if off the right edge of screen)

note 1) Displays character on bottom line of *physical*

screen, regardless of current size of window

(even entirely hidden)

2) Does not know about graphics display modes,

just pokes the characters into display memory

0Bh APILEVEL Define Minimum API Level Required

BL API level

>2 pops up "You need a newer version" error

window in DV 2.00

BH unknown

return AX maximum API level?

0Ch GETMEM Allocate "System" Memory

BX number of bytes

return ES:DI pointer to allocated block

0Dh PUTMEM Deallocate "System" Memory

ES:DI pointer to previously allocated block

return nothing

0Eh Find Mailbox by Name (DV 2.0+)

ES:DI pointer to name to find

CX length of name

return BX 0 not found

1 found

DS:SI object handle

0Fh Enable DesQview Extensions (DV 2.0+)

return AX and BX destroyed (seems to be bug, weren't

saved & restored)

note 1) Sends a manager stream with opcodes AEh, BDh,

and BFh to task's window

2) Enables an additional mouse mode

10h PUSHKEY PUT KEY INTO KEYBOARD INPUT STREAM (DV 2.0+)

BH scan code

BL character

return BX unknown (sometimes, but not always,

same as BX passed in)

note A later read will get the keystroke as if it

had been typed by the user

11h ENABLE/DISABLE AUTO JUSTIFICATION OF WINDOW (DV 2.0+)

BL 0 viewport will not move automatically

nonzero viewport will move to keep cursor

visible

return none

12h unknown (DV 2.0+)

BX 0 clear something?

nonzero set something?

return none

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 16h Keyboard I/O ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0058h) access the keyboard

Function 00h Get Keyboard Input - read the next character in keyboard buffer,

if no key ready, wait for one.

entry AH 00h

return AH scan code

AL ASCII character

Function 01h Check Keystroke Buffer - Do Not Clear

entry AH 01h

return ZF 0 (clear) if character in buffer

1 (set) if no character in buffer

AH scan code of character (if ZF=0)

AL ASCII character if applicable

note Keystroke is not removed from buffer

Function 02h Shift Status - fetch bit flags indicating shift status

entry AH 02h

return AL bit codes (same as [0040:0017])

bit 7 Insert state

bit 6 CapsLock state

bit 5 NumLock state

bit 4 ScrollLock state

bit 3 Alt key

bit 2 Control key

bit 1 Left shift (left caps-shift key)

bit 0 Right shift (right caps-shift key)

note other codes found at [0040:0018]

bit 7 Insert shift (Ins key)

bit 6 Caps shift (CapsLock key)

bit 5 Num shift (NumLock key)

bit 4 Scroll shift (ScrollLock key)

bit 3 Hold state (Ctrl-NumLock is in effect)

Function 03h Keyboard - Set Repeat Rate (PCjr, AT, XT/286, PS/2)

entry AH 03h

AL 00h reset typematic (PCjr)

01h increase initial delay (PCjr)

02h increase continuing delay (PCjr)

03h increase both delays (PCjr)

04h turn off typematic (PCjr)

05h set typematic rate (AT, PS/2)

BH 00h-03h for delays of 250ms, 500ms, 750ms, or 1second

0,0 250ms

0,1 500ms

1,0 750ms

1,1 1 second

BL 00h-1Fh for typematic rates of 30cps down to 2cps

00000 30 01011 10.9 10101 4.5

00001 26.7 01100 10 10110 4.3

00010 24 01101 9.2 10111 4

00011 21.8 01110 8.6 11000 3.7

00100 20 01111 8 11001 3.3

00101 18.5 10000 7.5 11010 3

00110 17.1 10001 6.7 11011 2.7

00111 16 10010 6 11100 2.5

01000 15 10011 5.5 11101 2.3

01001 13.3 10011 5.5 11110 2.1

01010 12 10100 5 11111 2

Function 04h Keyboard Click Toggle (PCjr and Convertible)

entry AH 04h

AL 00h for click off

01h for click on

Function 05h Keyboard Buffer Write (AT or PS/2 with enhanced kbd)

(XT/286, PS/2, AT with "Enhanced" keyboard)

entry AH 05h

CH scan code

CL ASCII character

return AL 01h if buffer full

Function 10h Get Enhanced Keystroke And Read (F11, F12 Enhanced Keyb'd)

(XT/286, PS/2, AT with "Enhanced" keyboard)

entry AH 10h

return AH scan code

AL ASCII character if applicable

Function 11h Check Enhanced Keystroke (F11-F12 on enhanced keyboard)

(XT/286, PS/2, AT with "Enhanced" keyboard)

entry AH 11h

return ZF 0 (clear) if key pressed

1 if buffer empty

AH scan code (when ZF=0)

AL ASCII character if applicable (when ZF=0)

note Keystroke is not removed from buffer

Function 12h Extended Get Shift Status (F11, F12 Enhanced keyboard)

entry AH 12h

return AL bit

0 right Shift key depressed

1 left Shift key depressed

2 Control key depressed

3 Alt key depressed

4 ScrollLock state active

5 NumLock state active

6 CapsLock state active

7 insert state is active

AH 0 left Control key pressed

1 left Alt key depressed

2 right Control key pressed

3 right Alt key depressed

4 Scroll Lock key depressed

5 NumLock key depressed

6 CapsLock key depressed

7 SysReq key depressed

Function F0h Set CPU speed (Compaq 386)

entry AH F0h set speed

return unknown

note used by Compaq DOS MODE command.

parameters not availible

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 17h Printer ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:005Ch) access the parallel printer(s)

AH is changed. All other registers left alone.

Function 00h Print Character/send AL to printer DX (0, 1, or 2)

entry AH 00h

AL character

DX printer to be used (0,1,2)

return AH status byte

bit

0 time out

1 unused

2 unused

3 I/O error

4 selected

5 out of paper

6 acknowledge

7 not busy

Function 01h Initialize Printer - set init line low, send 0Ch to printer DX

entry AH 01h

DX printer port to be initialized (0,1,2)

return status as below

Function 02h Printer Status - read status of printer DX into AH

entry AH 02h

DX printer port to be used (0,1,2)

return AH bit flags bit 7 0 = printer is busy

bit 6 ACKnowledge line state

bit 5 out-of-paper line state

bit 4 printer selected line state

bit 3 I/O error

bit 2 unused

bit 1 unused

bit 0 time-out error

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 18h ROM BASIC ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0060h) Execute ROM BASIC at address 0F600h:0000h

note 1) Often reboots a compatible

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 19h Bootstrap Loader ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0064h) Reads track 0, sector 1 into address 0000h:7C00h, then transfers

control to that address. If no diskette drive available,

transfers to ROM-BASIC or displays loader error message.

Causes reboot of disk system if invoked while running.

(no memory test performed).

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³Interrupt 1Ah Time of Day ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0068h) access the PC internal clock

Function 00h Read System Time Counter

entry AH 00h

return CX high word of clock count

DX low word of clock count

AL 00h if clock was read or written (via AH=0,1) within the current

24-hour period. Otherwise, AL > 0

Function 01h Set Clock - set # of 55ms clock ticks in system time counter

entry AH 01h

CX:DX high word/low word count of timer ticks

return none

note 1) The clock ticks are incremented by timer interrupt at 18.2065 times

per second or 54.9254milliseconds/count. Therefore:

counts per second = 18 (12h)

counts per minute = 1092 (444h)

counts per hour = 65543 (10011h)

counts per day = 1573040 (1800B0h)

2) counter is zeroed when system is rebooted

Function 02h Read Real Time Clock Time (AT and after)

entry AH 02h

return CH hours in BCD

CL minutes in BCD

DH seconds in BCD

DL 1 (set) if daylight savings time option

CF 1 (set) if clock not operating

Function 03h Set Real Time Clock Time (AT and after)

entry AH 03h

CH hours in BCD

CL minutes in BCD

DH seconds in BCD

DL 0 (clear) if standard time

1 (set) if daylight savings time option

return none

Function 04h Read Real Time Clock Date (AT and after)

entry AH 04h

return CH century in BCD (19 or 20)

CL year in BCD

DH month in BCD

DL day in BCD

CF 1 (set) if clock not operating

Function 05h Set Real Time Clock Date (AT and after)

entry AH 05h

CH century in BCD (19 or 20)

CL year in BCD

DH month in BCD

DL day in BCD

return none

Function 06h Set Real Time Clock Alarm (AT and after)

entry AH 06h

CH hours in BCD

CL minutes in BCD

DH seconds in BCD

return CF set if alarm already set or clock inoperable

note Int 4Ah occurs at specified alarm time every 24hrs until reset

Function 07h Reset Real Time Clock Alarm (AT and after)

entry AH 07h

return none

Function 08h Set Real Time Clock Activated Power On Mode (Convertible)

entry AH 08h

CH hours in BCD

CL minutes in BCD

DH seconds in BCD

Function 09h Read Real Time Clock Alarm Time and Status

(Convertible and PS/2 Model 30)

entry AH 09h

return CH hours in BCD

CL minutes in BCD

DH seconds in BCD

DL alarm status:

00h if alarm not enabled

01h if alarm enabled but will not power up system

02h if alarm will power up system

Function 0Ah Read System-Timer Day Counter (XT-2 [640k motherboard], PS/2)

entry AH 0Ah

return CF set on error

CX count of days since Jan 1,1980

Function 0Bh Set System-Timer Day Counter (XT-2 [640k motherboard], PS/2)

entry AH 0Bh

CX count of days since Jan 1,1980

return CF set on error

Function 80h Set Up Sound Multiplexor (PCjr) (Tandy 1000?)

entry AH 80h

AL 00h source is 8253 channel 2

01h source is cassette input

02h source is I/O channel "audio in"

03h source is TI sound generator chip

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³Interrupt 1Bh Control-Break ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:006Ch) This interrupt is called when the keyboard scanner of the IBM

machines detects Ctrl and Break pressed at the same time.

note 1) If the break occurred while processing an interrupt, one or more

end of interrupt commands must be send to the 8259 Programmable

Interrupt Controller.

2) All I/O devices should be reset in case an operation was underway at

the time.

3) It is normally pointed to an IRET during system initialization so that

it does nothing, but some programs change it to return a ctrl-C scan

code and thus invoke int 23h.

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³Interrupt 1Ch Timer Tick ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0070h)

note 1) Taken 18.2065 times per second

2) Normally vectors to dummy IRET unless PRINT.COM has been installed.

3) If an application moves the interrupt pointer, it is the responsibility

of that application to save and restore all registers that may be

modified.

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³Interrupt 1Dh Vector of Video Initialization Parameters ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0074h) This doubleword address points to 3 sets of 16-bytes containing

data to initialize for video modes for video modes 0 & 1 (40

column), 2 & 3 (80 column), and 4, 5 & 6 (graphics) on the

Motorola 6845 CRT controller chip.

6845 registers:

R0 horizontal total (horizontal sync in characters)

R1 horizontal displayed (characters per line)

R2 horizontal sync position (move display left or right)

R3 sync width (vertical and horizontal pulse: 4-bits each)

R4 vertical total (total character lines)

R5 vertical adjust (adjust for 50 or 60 Hz refresh)

R6 vertical displayed (lines of chars displayed)

R7 vertical sync position (lines shifted up or down)

R8 interlace (bits 4 and 5) and skew (bits 6 and 7)

R9 max scan line addr (scan lines per character row)

R10 cursor start (starting scan line of cursor)

R11 cursor stop (ending scan line of cursor)

R12 video memory start address high byte (6-bits)

R13 video memory start address low byte (8-bits)

R14 cursor address high byte (6-bits)

R15 cursor address low byte (8-bits)

6845 Video Init Tables:

table for modes 0 and 1 \

table for modes 2 and 3 \ each table is 16 bytes long and

table for modes 4,5, and 6 / contains values for 6845 registers

table for mode 7 /

4 words: size of video RAM for modes 0/1, 2/3, 4/5, and 6/7

8 bytes: number of columns in each mode

8 bytes: video controller mode byte for each mode

note 1) There are 4 separate tables, and all 4 must be initialized if all

video modes will be used.

2) The power-on initialization code of the computer points this vector

to the ROM BIOS video routines.

3) IBM recommends that if this table needs to be modified, it should be

copied into RAM and only the nescessary changes made.

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³Interrupt 1Eh Vector of Diskette Controller Parameters ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0078h) Dword address points to data base table that is used by BIOS.

Default location is at 0F000:0EFC7h. 11-byte table format:

bytes:

00h 4-bit step rate, 4-bit head unload time

01h 7-bit head load time, 1-bit DMA flag

02h 54.9254 ms counts - delay till motor off (37-38 typ)

03h sector size:

00h 128 bytes

01h 256 bytes

02h 512 bytes

03h 1024 bytes

04h last sector on track (8 or 9 typical)

05h gap between sectors on read/write (42 typical)

06h data length for DMA transfers (0FFh typical)

07h gap length between sectors for format (80 typical)

08h sector fill byte for format (0F6h typical)

09h head settle time (in milliseconds) (15 to 25 typical)

DOS 1.0 0

DOS 2.10 15

DOS 3.1 1

10h motor start time (in 1/8 second intervals) (2 to 4 typ.)

DOS 2.10 2

note 1) This vector is pointed to the ROM BIOS diskette tables on system

initialization

2) IBM recommends that if this table needs to be modified, it should be

copied into RAM and only the nescessary changes made.

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³Interrupt 1Fh Pointer to Graphics Character Extensions (Graphics Set 2) ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:007Ch) This is the pointer to data used by the ROM video routines to

display characters above ASCII 127 while in CGA medium and high

res graphics modes.

note 1) Doubleword address points to 1K table composed of 28 8-byte character

definition bit-patterns. First byte of each entry is top row, last byte

is bottom row.

2) The first 128 character patterns are located in system ROM.

3) This vector is set to 000:0 at system initialization

4) Used by DOS' external GRAFTABL command

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³Interrupt 20h Terminate Current Program ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0080h)

Issue int 20h to exit from a program. This vector transfers to the logic in

DOS to restore the terminate address, the Ctrl-Break address,and the critical

error exit address to the values they had on entry to the program. All the file

buffers are flushed and all handles are closed. You should close all files

changed in length (see function calls 10h and 3Eh) before issuing this

interrupt. If the changed file is not closed, its length, time, and date are

not recorded correctly in the directory.

For a program to pass a completion code or an error code when terminating, it

must use either function call 4Ch (Terminate a Process) or 31h (Terminate

Process and Stay Resident). These two methods are preferred over using

int 20h and the codes returned by them can be interrogated in batch processing.

Important: Before you issue an interrupt 20h, your program must ensure that

the CS register contains the segment of its program segment prefix.

Interrupt 20h DOS - Terminate Program

entry no parameters

return The following vectors are restored from the Program Segment Prefix:

0Ah Program Terminate

0Eh Control-C

12h Critical Error

note IBM and Microsoft recommend using int 21 Fn 4Ch. Using int 20 is

officially frowned upon since the introduction of DOS 2.0

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

C H A P T E R F O U R

DOS INTERRUPTS AND FUNCTION CALLS

note: The registered version of this chapter is twice this size.

DOS REGISTERSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

DOS uses the following registers, pointers, and flags when it executes

interrupts and function calls:

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³GENERAL REGISTERS ³ register ³ definition ³

³ ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ AX ³ accumulator (16 bit) ³

³ ³ AH ³ accumulator high-order byte (8 bit) ³

³ ³ AL ³ accumulator low order byte (8 bit) ³

³ ³ BX ³ base (16 bit) ³

³ ³ BH ³ base high-order byte (8 bit) ³

³ ³ BL ³ base low-order byte (8 bit) ³

³ ³ CX ³ count (16 bit) ³

³ ³ CH ³ count high order byte (8 bit) ³

³ ³ CL ³ count low order byte (8 bit) ³

³ ³ DX ³ data (16 bit) ³

³ ³ DH ³ date high order byte (8 bit) ³

³ ³ DL ³ data low order byte (8 bit) ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³SEGMENT REGISTERS ³ register ³ definition ³

³ ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ CS ³ code segment (16 bit) ³

³ ³ DS ³ data segment (16 bit) ³

³ ³ SS ³ stack segment (16 bit) ³

³ ³ ES ³ extra segment (16 bit) ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³INDEX REGISTERS ³ register ³ definition ³

³ ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ DI ³ destination index (16 bit) ³

³ ³ SI ³ stack index (16 bit) ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³SEGMENT REGISTERS ³ register ³ definition ³

³ ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ CS ³ code segment (16 bit) ³

³ ³ DS ³ data segment (16 bit) ³

³ ³ SS ³ stack segment (16 bit) ³

³ ³ ES ³ extra segment (16 bit) ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³INDEX REGISTERS ³ register ³ definition ³

³ ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ DI ³ destination index (16 bit) ³

³ ³ SI ³ stack index (16 bit) ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³POINTERS ³ register ³ definition ³

³ ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ SP ³ stack pointer (16 bit) ³

³ ³ BP ³ base pointer (16 bit) ³

³ ³ IP ³ instruction pointer (16 bit) ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³FLAGS AF, CF, DF, IF, OF, PF, SF, TF, ZF ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

These registers, pointers, and flags are "lowest common denominator" 8088-8086

CPU oriented. DOS makes no attempt to use any of the special or enhanced

instructions availible on the later CPUs which will execute 8088 code, such as

the 80186, 80286, 80386, or NEV V20, V30, V40, or V50.

When DOS takes control after a function call, it switches to an internal

stack. Registers which are not used to return information (other than AX) are

preserved. The calling program's stack must be large enough to accomodate the

interrupt system - at least 128 bytes in addition to other interrupts.

DOS actually maintains three stacks -

stack 1: 384 bytes (in DOS 3.1)

for functions 00h and for 0Dh and up, and for ints 25h and 26h.

stack 2: 384 bytes (in DOS 3.1)

for function calls 01h through 0Ch.

stack 3: 48 bytes (in DOS 3.1)

for functions 0Dh and above. This stack is the initial stack used by

the int 21h handler before it decides which of the other two to use.

It is also used by function 59h (get extended error), and 01h to 0Ch if

they are called during an int 24h (critical error) handler. Functions

33h (get/set break flag), 50h (set process ID), 51h (get process ID)

and 62h (get PSP address) do not use any DOS stack under DOS 3.x

(under 2.x, 50h and 51h use stack number 2).

IBM and Microsoft made a change back in DOS 3.0 or 3.1 to reduce the size of

DOS. They reduced the space allocated for scratch areas when interrupts are

being processed. The default seems to vary with the DOS version and the

machine, but 8 stack frames seems to ring a bell. That means that if you get

more than 8 interrupts at the same time, clock, disk, printer spooler,

keyboard, com port, etc., the system will crash. It seems to happen usually on

a network. STACKS=16,256 means allow 16 interrupts to interrupt each other and

allow 256 bytes for each for scratch area. Eight is marginal.

DOS 3.2 does some different stack switching than previous versions. The

interrupts which are switched are 02h, 08h, 09h, 0Ah, 0Bh, 0Ch, 0Dh, 0Eh, 70h,

72h, 73h, 74h, 75h, 76h, and 77h. DOS 3.2 has a special check in the

initialization code for a PCjr and don't enable stack switching on that machine.

INTERRUPTSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Microsoft recommends that a program wishing to examine or set the contents of

any interrupt vector use the DOS function calls 35h and 25h provided for those

purposes and avoid referencing the interrupt vector locations directly.

DOS reserves interrupt numbers 20h to 3Fh for its own use. This means absolute

memory locations 80h to 0FFh are reserved by DOS. The defined interrupts are as

follows with all values in hexadecimal.

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³Interrupt 21h Function Call Request ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

(0:0084h)

DOS provides a wide variety of function calls for character device I/O, file

management, memory management, date and time functions,execution of other

programs, and more. They are grouped as follows:

call description

00h program terminate

01h-0Ch character device I/O, CP/M compatibility format

0Dh-24h file management, CP/M compatibility format

25h-26h nondevice functions, CP/M compatibility format

27h-29h file management, CP/M compatibility format

2Ah-2Eh nondevice functions, CP/M compatibility format

2Fh-38h extended functions

39h-3Bh directory group

3Ch-46h extended file management

47h directory group

48h-4Bh extended memory management

54h-57h extended functions

5Eh-5Fh networking

60h-62h extended functions

63h-66h enhanced foreign language support

List of DOS services: * = undocumented

00h terminate program

01h get keyboard input

02h display character to STDIO

03h get character from STDAUX

04h output character to STDAUX

05h output character to STDPRN

06h direct console I/O - keyboard to screen

07h get char from std I/O without echo

08h get char from std I/O without echo, checks for ^C

09h display a string to STDOUT

0Ah buffered keyboard input

0Bh check STDIN status

0Ch clear keyboard buffer and invoke keyboard function

0Dh flush all disk buffers

0Eh select disk

0Fh open file with File Control Block

10h close file opened with File Control Block

11h search for first matching file entry

12h search for next matching file entry

13h delete file specified by File Control Block

14h sequential read from file specified by File Control Block

15h sequential write to file specified by File Control Block

16h find or create firectory entry for file

17h rename file specified by file control block

18h* unknown

19h return current disk drive

1Ah set disk transfer area (DTA)

1Bh get current disk drive FAT

1Ch get disk FAT for any drive

1Dh* unknown

1Eh* unknown

1Fh* read DOS disk block, default drive

20h* unknown

21h random read from file specified by FCB

22h random write to file specified by FCB

23h return number of records in file specified by FCB

24h set relative file record size field for file specified by FCB

25h set interrupt vector

26h create new Program Segment Prefix (PSP)

27h random file block read from file specified by FCB

28h random file block write to file specified by FCB

29h parse the command line for file name

2Ah get the system date

2Bh set the system date

2Ch get the system time

2Dh set the system time

2Eh set/clear disk write VERIFY

2Fh get the Disk Transfer Address (DTA)

30h get DOS version number

31h TSR, files opened remain open

32h* read DOS Disk Block

33h get or set Ctrl-Break

34h* INDOS Critical Section Flag

35h get segment and offset address for an interrupt

36h get free disk space

37h* get/set option marking character (SWITCHAR)

38h return country-dependent information

39h create subdirectory

3Ah remove subdirectory

3Bh change current directory

3Ch create and return file handle

3Dh open file and return file handle

3Eh close file referenced by file handle

3Fh read from file referenced by file handle

40h write to file referenced by file handle

41h delete file

42h move file pointer (move read-write pointer for file)

43h set/return file attributes

44h device IOCTL (I/O control) info

45h duplicate file handle

46h force a duplicate file handle

47h get current directory

48h allocate memory

49h release allocated memory

4Ah modify allocated memory

4Bh load or execute a program

4Ch terminate prog and return to DOS

4Dh get return code of subprocess created by 4Bh

4Eh find first matching file

4Fh find next matching file

50h* set new current Program Segment Prefix (PSP)

51h* puts current PSP into BX

52h* pointer to the DOS list of lists

53h* translates BPB (Bios Parameter Block, see below)

54h get disk verification status (VERIFY)

55h* create PSP: similar to function 26h

56h rename a file

57h get/set file date and time

58h get/set allocation strategy (DOS 3.x)

59h get extended error information

5Ah create a unique filename

5Bh create a DOS file

5Ch lock/unlock file contents

5Dh* network

5Eh* network printer

5Fh* network redirection

60h* parse pathname

61h* unknown

62h get program segment prefix (PSP)

63h* get lead byte table (DOS 2.25)

64h* unknown

65h get extended country information (DOS 3.3)

66h get/set global code page table (DOS 3.3)

67h set handle count (DOS 3.3)

68h commit file (DOS 3.3)

69h disk serial number (DOS 4.0)

6Ah unknown

6Bh unknown

6Ch extended open/create (DOS 4.0)

CALLING THE DOS SERVICESÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The DOS services are invoked by placing the number of the desired function in

requirements of the function, and invoking int 21h.

On return, the requested service will be performed if possible. Most codes

will return an error; some return more information. Details are contained in

the listings for the individual functions. Extended error return may be

obtained by calling function 59h (see 59h).

with garbage values in unused registers. Do not test for values in unspecified

registers; your program may exhibit odd behavior.

DS:DX pointers are the data segment register (DS) indexed to the DH and DL

registers (DX). DX always contains the offset address, DS contains the segment

address.

The File Control Block services (FCB services) were part of DOS 1.0. Since

the release of DOS 2.0, Microsoft has recommended that these services not be

used. A set of considerably more enhanced services (handle services) were

introduced with DOS 2.0. The handle services provide support for wildcards and

subdirectories, and enhanced error detection via function 59h.

The data for the following calls was compiled from various Intel, Microsoft,

IBM, and other publications. There are many subtle differences between MSDOS

and PCDOS and between the individual versions. Differences between the

versions are noted as they occur.

There are various ways of calling the DOS functions. For all methods, the

function number is loaded into register AH, subfunctions and/or parameters are

loaded into AL or other registers, and call int 21 by one of the following

methods:

A) call interrupt 21h directly (the recommended procedure)

B) perform a long call to offset 50h in the program's PSP.

1) This method will not work under DOS 1.x

2) Though recommended by Microsoft for DOS 2.0, this method takes more

time and is no longer recommended.

C) place the function number in CL and perform an intrasegment call to

location 05h in the current code segment. This location contains a long

call to the DOS function dispatcher.

1) IBM recommends this method be used only when using existing programs

written for different calling conventions. (such as converting CP/M

programs). This method should be avoided unless you have some specific

use for it.

2) AX is always destroyed by this method.

3) This method is valid only for functions 00h-24h.

There are also various ways of exiting from a program. (assuming it is not

intended to be a TSR). All methods except call 4Ch must ensure that the

segment register contains the segment address of the PSP.

A) Interrupt 21h, function 4Ch (Terminate with Result Code). This is the

"official" recommended method of returning to DOS.

B) Interrupt 21h, function 00h (Exit Program). This is the early style

int 21 function call. It simply calls int 20h.

C) Interrupt 20h (Exit).

D) A JMP instruction to offset 00h (int 20h vector) in the Program Segment

Prefix. This is just a roundabout method to call int 20h. This method

was set up in DOS 1.0 for ease of conversion for CP/M programs. It is no

longer recommended for use.

E) A JMP instruction to offset 05h (int 21 vector) in the Program Segment

Prefix, with AH set to 00h or 4Ch. This is another CP/M type function.

INT 21H DOS services

Function (hex)

* Indicates Functions not documented in the IBM DOS Technical Reference.

Note some functions have been documented in other Microsoft or licensed OEM

documentation.

Function 00h Terminate Program

Ends program, updates, FAT, flushes buffers, restores registers

entry AH 00h

CS segment address of PSP

return none

note 1) Program must place the segment address of the PSP control block in CS

before calling this function.

2) The terminate, ctrl-break,and critical error exit addresses (0Ah, 0Eh,

12h) are restored to the values they had on entry to the terminating

program, from the values saved in the program segment prefix at

locations PSP:000Ah, PSP:000Eh, and PSP:0012h.

3) All file buffers are flushed and the handles opened by the process are

closed.

4) Any files that have changed in length and are not closed are not

recorded properly in the directory.

5) Control transfers to the terminate address.

6) This call performs exactly the same function as int 20h.

7) All memory used by the program is returned to DOS.

Function 01h Get Keyboard Input

Waits for char at STDIN (if nescessary), echoes to STDOUT

entry AH 01h

return AL ASCII character from STDIN (8 bits)

note 1) Checks char for Ctrl-C, if char is Ctrl-C, executes int 23h.

2) For function call 06h, extended ASCII codes require two function calls.

The first call returns 00h as an indicator that the next call will be an

extended ASCII code.

3) Input and output are redirectable. If redirected, there is no way to

detect EOF.

Function 02h Display Output

Outputs char in DL to STDOUT

entry AH 02h

DL 8 bit data (usually ASCII character)

return none

note 1) If char is 08 (backspace) the cursor is moved 1 char to the left

(nondestructive backspace).

2) If Ctrl-C is detected after input, int 23h is executed.

3) Input and output are redirectable. If redirected, there is no way to

detect disk full.

Function 03h Auxiliary Input

Get (or wait until) character from STDAUX

entry AH 03h

return AL char from auxiliary device

note 1) AUX, COM1, COM2 is unbuffered and not interrupt driven

2) This function call does not return status or error codes. For greater

control it is recommended that you use ROM BIOS routine (int 14h) or

write an AUX device driver and use IOCTL.

3) At startup, PC-DOS initializes the first auxiliary port (COM1) to 2400

baud, no parity, one stop bit, and an 8-bit word. MSDOS may differ.

4) If Ctrl-C is has been entered from STDIN, int 23h is executed.

Function 04h Auxiliary Output

Write character to STDAUX

entry AH 04h

DL char to send to AUX

return none

note 1) This function call does not return status or error codes. For greater

control it is recommended that you use ROM BIOS routine (int 14h) or

write an AUX device driver and use IOCTL.

2) If Ctrl-C is has been entered from STDIN, int 23h is executed.

3) Default is COM1 unless redirected by DOS.

4) If the device is busy, this function will wait until it is ready.

Function 05h Printer Output

Write character to STDPRN

entry AL 05h

DL character to send

return none

note 1) If Ctrl-C is has been entered from STDIN, int 23h is executed.

2) Default is PRN or LPT1 unless redirected with the MODE command.

3) If the printer is busy, this function will wait until it is ready.

Function 06h Direct Console I/O

Get character from STDIN; echo character to STDOUT

entry AH 06h

DL 0FFh for console input, or 00h-0FEh for console output

return ZF set (1) = no character

clear (0) = character recieved

AL character

note 1) Extended ASCII codes require two function calls. The first call returns

00h to indicate the next call will return an extended code.

2) If DL is not 0FFh, DL is assumed to have a valid character that is

output to STDOUT.

3) This function does not check for Ctrl-C or Ctrl-PrtSc.

4) Does not echo input to screen

5) If I/O is redirected, EOF or disk full cannot be detected.

Function 07h Direct Console Input Without Echo (does not check BREAK)

Get or wait for char at STDIN, returns char in AL

entry AH 07h

return AL character from standard input device

note 1) Extended ASCII codes require two function calls. The first call returns

00h to indicate the next call will return an extended code.

2) No checking for Ctrl-C or Ctrl-PrtSc is done.

3) Input is redirectable.

Function 08h Console Input Without Echo (checks BREAK)

Get or Wait for char at STDIN, return char in AL

entry AH 08h

return AL char from standard input device

note 1) Char is checked for ctrl-C. If ctrl-C is detected, executes int 23h.

2) For function call 08h, extended ASCII characters require two function

calls. The first call returns 00h to signify an extended ASCII code.

The next call returns the actual code.

3) Input is redirectable. If redirected, there is no way to check EOF.

Function 09h Print String

Outputs Characters in the Print String to the STDOUT

entry AH 09h

DS:DX pointer to the Character String to be displayed

return none

note 1) The character string in memory must be terminated by a $ (24h)

The $ is not displayed.

2) Output to STDOUT is the same as function call 02h.

Function 0Ah Buffered Keyboard Input

Reads characters from STDIN and places them in the buffer beginning

at the third byte.

entry AH 0Ah

DS:DX pointer to an input buffer

return none

note 1) Min buffer size = 1, max = 255

2) Char is checked for ctrl-C. If ctrl-C is detected, executes int 23h.

3) Format of buffer DX:

byte contents

1 Maximum number of chars the buffer will take, including CR.

Reading STDIN and filling the buffer continues until a carriage

return (<Enter> or 0Dh) is read. If the buffer fills to one less

than the maximum number the buffer can hold, each additional

number read is ignored and ASCII 7 (BEL) is output to the

display until a carriage return is read. (you must set this

value)

2 Actual number of characters received, excluding the carriage

return, which is always the last character. (the function sets

this value)

3-n Characters received are placed into the buffer starting here.

Buffer must be at least as long as the number in byte 1.

4) Input is redirectable. If redirected, there is no way to check EOF.

5) The string may be edited with the standard DOS editing commands as it

is being entered.

6) Extended ASCII characters are stored as 2 bytes, the first byte being

zero.

Function 0Bh Check Standard Input (STDIN) status

Checks for character availible at STDIN

entry AH 0Bh

return AL 0FFh if a character is availible from STDIN

00h if no character is availible from STDIN

note 1) Checks for Ctrl-C. If Ctrl-C is detected, int 23h is executed

2) Input can be redirected.

3) Checks for character only, it is not read into the application

4) IBM reports that this call does not work properly under the DOSSHELL

program in DOS 4.00 and 4.01. DOSSHELL will return all zeroes. This

function works correctly from the command line or application.

Function 0Ch Clear Keyboard Buffer & Invoke a Keyboard Function (FCB)

Dumps buffer, executes function in AL (01h,06h,07h,08h,0Ah only)

entry AH 0Ch

AL function number (must be 01h, 06h, 07h, 08h, or 0Ah)

return AL 00h buffer was flushed, no other processing performed

other any other value has no meaning

note 1) Forces system to wait until a character is typed.

2) Flushes all typeahead input, then executes function specified by AL (by

moving it to AH and repeating the int 21 call).

3) If AL contains a value not in the list above, the keyboard buffer is

flushed and no other action is taken.

Function 0Dh Disk Reset

Flushes all currently open file buffers to disk

entry AH 0Dh

return none

note 1) Does not close files. Does not update directory entries; files changed

in size but not closed are not properly recorded in the directory

2) Sets DTA address to DS:0080h

3) Should be used before a disk change, Ctrl-C handlers, and to flush

the buffers to disk.

Function 0Eh Select Disk

Sets the drive specified in DL (if valid) as the default drive

entry AL 0Eh

DL new default drive number (0=A:,1=B:,2=C:,etc.)

return AL total number of logical drives (not nescessarily physical)

note 1) For DOS 1.x and 2.x, the minimum value for AL is 2.

2) For DOS 3.x and 4.x, the minimum value for AL is 5.

3) The drive number returned is not nescessarily a valid drive.

4) For DOS 1.x: 16 logical drives are availible, A-P.

For DOS 2.x: 63 logical drives are availible. (Letters are only used for

the first 26 drives. If more than 26 logical drives are

used, further drive letters will be other ASCII characters

ie {,], etc.

For DOS 3.x: 26 logical drives are availible, A-Z.

For DOS 4.x: 26 logical drives are availible, A-Z.

Function 0Fh Open Disk File (FCB)

Searches current directory for specified filename and opens it

entry AH 0Fh

DS:DX pointer to an unopened FCB

return AL 00h if file found

0FFh if file not not found

note 1) If the drive code was 0 (default drive) it is changed to the actual

drive used (1=A:,2=B:,3=C:, etc). This allows changing the default drive

without interfering with subsequent operations on this file.

2) The current block field (FCB bytes C-D, offset 0Ch) is set to zero.

3) The size of the record to be worked with (FCB bytes E-F, offset 0Eh) is

set to the system default of 80h. The size of the file (offset 10h) and

the date (offset 14h) are set from information obtained in the root

directory. You can change the default value for the record size (FCB

bytes E-F) or set the random record size and/or current record field.

Perform these actions after the open but before any disk operations.

4) The file is opened in compatibility mode.

5) Microsoft recommends handle function call 3Dh be used instead.

6) This call is also used by the APPEND command in DOS 3.2+

7) Before performing a sequential disk operation on the file, you must

set the Current Record field (offset 20h). Before performing a random

disk operation on the file, you must set the Relative Record field

(offset 21h). If the default record size of 128 bytes is incorrect, set

it to the correct value.

Function 10h Close File (FCB)

Closes a File After a File Write

entry AH 10h

DS:DX pointer to an opened FCB

return AL 00h if the file is found and closed

0FFh if the file is not found in the current directory

note 1) This function call must be done on open files that are no longer needed,

and after file writes to insure all directory information is updated.

2) If the file is not found in its correct position in the current

directory, it is assumed that the diskette was changed and AL returns

0FFh. This error return is reportedly not completely reliable with DOS

version 2.x.

3) If found, the directory is updated to reflect the status in the FCB, the

buffers to that file are flushed, and AL returns 00h.

Function 11h Search For First Matching Entry (FCB)

Searches current disk & directory for first matching filename

entry AH 11h

DS:DX pointer to address of FCB

return AL 00h successful match

0FFh no matching filename found

note 1) The FCB may contain the wildcard character ? under Dos 2.x, and ? or *

under 3.x and 4.x.

2) The original FCB at DS:DX contains information to continue the search

with function 12h, and should not be modified.

3) If a matching filename is found, AL returns 00h and the locations at the

Disk Transfer Address are set as follows:

a) If the FCB provided for searching was an extended FCB, then the first

byte at the disk transfer address is set to 0FFh followed by 5 bytes

of zeroes, then the attribute byte from the search FCB, then the

drive number used (1=A, 2=B, etc) then the 32 bytes of the directory

entry. Thus, the disk transfer address contains a valid unopened FCB

with the same search attributes as the search FCB.

b) If the FCB provided for searching was a standard FCB, then the first

byte is set to the drive number used (1=A,2=b,etc), and the next 32

bytes contain the matching directory entry. Thus, the disk transfer

address contains a valid unopened normal FCB.

4) If an extended FCB is used, the following search pattern is used:

a) If the FCB attribute byte is zero, only normal file entries are

found. Entries for volume label, subdirectories, hidden or system

files, are not returned.

b) If the attribute byte is set for hidden or system files, or

subdirectory entries, it is to be considered as an inclusive search.

All normal file entries plus all entries matching the specified

attributes are returned. To look at all directory entries except the

volume label, the attribute byte may be set to hidden + system +

directory (all 3 bits on).

c) If the attribute field is set for the volume label, it is considered

an exclusive search, and ONLY the volume label entry is returned.

5) This call is also used by the APPEND command in DOS 3.2+

Function 12h Search For Next Entry Using FCB (FCB)

Search for next matching filename

entry AH 12h

DS:DX pointer to the unopened FCB specified from the previous Search

First (11h) or Search Next (12h)

return AL 00h if matching filename found

0FFh if matching filename was not found

note 1) After a matching filename has been found using function call 11h,

function 12h may be called to find the next match to an ambiguous

request. For DOS 2.x, ?'s are allowed in the filename. For DOS 3.x

and 4.x, global (*) filename characters are allowed.

2) The DTA contains info from the previous Search First or Search Next.

3) All of the FCB except for the name/extension field is used to keep

information nescessary for continuing the search, so no disk operations

may be performed with this FCB between a previous function 11h or 12h

call and this one.

4) If the file is found, an FCB is created at the DTA address and set up to

open or delete it.

Function 13h Delete File Via FCB (FCB)

Deletes file specified in FCB from current directory

entry AH 13h

DS:DX pointer to address of FCB

return AL 00h file deleted

0FFh if file not found or was read-only

note 1) All matching current directory entries are deleted. The global filename

character "?" is allowed in the filename.

2) Will not delete files with read-only attribute set

3) Close open files before deleting them.

4) Requires Network Access Rights

Function 14h Sequential Disk File Read (FCB)

Reads record sequentially from disk via FCB

entry AH 14h

DS:DX pointer to an opened FCB

return AL 00h successful read

01h end of file (no data read)

02h Data Transfer Area too small for record size specified

or segment overflow

03h partial record read, EOF found

note 1) The record size is set to the value at offset 0Eh in the FCB.

2) The record pointed to by the Current Block (offset 0Ch) and the Current

Record (offset 20h) fields is loaded at the DTA, then the Current Block

and Current Record fields are incremented.

3) The record is read into memory at the current DTA address as specified

by the most recent call to function 1Ah. If the size of the record and

location of the DTA are such that a segment overflow or wraparound would

occur, the error return is set to AL=02h

4) If a partial record is read at the end of the file, it is passed to the

requested size with zeroes and the error return is set to AL=03h.

Function 15h Sequential Disk Write (FCB)

Writes record specified by FCB sequentially to disk

entry AH 15h

DS:DX pointer to address of FCB

return AL 00h successful write

01h diskette full, write canceled

02h disk transfer area (DTA) too small or segment wrap

note 1) The data to write is obtained from the disk transfer area

2) The record size is set to the value at offset 0Eh in the FCB.

3) This service cannot write to files set as read-only

4) The record pointed to by the Current Block (offset 0Ch) and the Current

Record (offset 20h) fields is loaded at the DTA, then the Current Block

and Current Record fields are incremented.

5) If the record size is less than a sector, the data in the DTA is written

to a buffer; the buffer is written to disk when it contains a full

sector of data, the file is closed, or a Reset Disk (function 0Dh) is

issued.

6) The record is written to disk at the current DTA address as specified

by the most recent call to function 1Ah. If the size of the record and

location of the DTA are such that a segment overflow or wraparound would

occur, the error return is set to AL=02h

Function 16h Create A Disk File (FCB)

Search and open or create directory entry for file

entry AH 16h

DS:DX pointer to an FCB

return AL 00h successful creation

0FFh no room in directory

note 1) If a matching directory entry is found, the file is truncated to zero

bytes.

2) If there is no matching filename, a filename is created.

3) This function calls function 0Fh (Open File) after creating or

truncating a file.

4) A hidden file can be created by using an extended FCB with the attribute

byte (offset FCB-1) set to 2.

Function 17h Rename File Specified by File Control Block (FCB)

Renames file in current directory

entry AH 17h

DS:DX pointer to an FCB (see note 4)

return AL 00h successfully renamed

0FFh file not found or filename already exists

note 1) This service cannot rename read-only files

2) The "?" wildcard may be used.

3) If the "?" wildcard is used in the second filename, the corresponding

letters in the filename of the directory entry are not changed.

4) The FCB must have a drive number, filename, and extension in the usual

position, and a second filename starting 6 bytes after the first, at

offset 11h.

5) The two filenames cannot have the same name.

6) FCB contains new name starting at byte 17h.

Function 18h Internal to DOS

* Unknown

entry AH 18h

return AL 0

Function 19h Get Current Disk Drive

Return designation of current default disk drive

entry AH 19h

return AL current default drive (0=A, 1=B,etc.)

note Some other DOS functions use 0 for default, 1=A, 2=B, etc.

Function 1Ah Set Disk Transfer Area Address (DTA)

Sets DTA address to the address specified in DS:DX

entry AH 1Ah

DS:DX pointer to buffer

return none

note 1) The default DTA is 128 bytes at offset 80h in the PSP. DOS uses the

DTA for all file I/O.

2) Registers are unchanged.

3) No error codes are returned.

2) Disk transfers cannot wrap around from the end of the segment to the

beginning or overflow into another segment.

Function 1Bh Get Current Drive File Allocation Table Information

Returns information from the FAT on the current drive

entry AH 1Bh

exit AL number of sectors per allocation unit (cluster)

DS:BX address of the current drive's media descriptor byte

CX number of bytes per sector

DX number of allocation units (clusters) for default drive

note 1) Save DS before calling this function.

2) This call returned a pointer to the FAT in DOS 1.x. Beginning with

DOS 2.00, it returns a pointer only to the table's ID byte.

3) IBM recommends programmers avoid this call and use int 25h instead.

Function 1Ch Get File Allocation Table Information for Specific Device

Returns information on specified drive

entry AH 1Ch

DL drive number (1=A, 2=B, 3=C, etc)

return AL number of sectors per allocation unit (cluster)

DS:BX address of media descriptor byte for drive in DL

CX sector size in bytes

DX number of allocation units (clusters)

note 1) DL = 0 for default.

2) Save DS before calling this function.

3) Format of media-descriptor byte:

bits: 0 0 (clear) not double sided

1 (set) double sided

1 0 (clear) not 8 sector

1 (set) 8 sector

2 0 (clear) nonremovable device

1 (set) removable device

3-7 always set (1)

4) This call returned a pointer to the FAT in DOS 1.x. Beginning with

DOS 2.00, it returns a pointer only to the table's ID byte.

5) IBM recommends programmers avoid this call and use int 25h instead.

Function 1Dh Not Documented by Microsoft

* Unknown

entry AH 1Dh

return AL 0

Function 1Eh Not Documented by Microsoft

* Unknown

entry AH 1Eh

return AL 0

note Apparently does nothing

Function 1Fh Get Default Drive Parameter Block

* Same as function call 32h (below), except that the table is accessed from

the default drive

entry AH 1Fh

other registers unknown

return AL 00h no error

0FFh error

DS:BX points to DOS Disk Parameter Block for default drive.

note 1) Unknown vector returned in ES:BX.

2) For DOS 2.x and 3.x, this just invokes function 32h (undocumented,

Read DOS Disk Block) with DL=0

Function 20h Unknown

* Internal - does nothing?

entry AH 20h

return AL 0

Function 21h Random Read from File Specified by File Control Block (FCB)

Reads one record as specified in the FCB into the current DTA.

entry AH 21h

DS:DX address of the opened FCB

return AL 00h successful read operation

01h end of file (EOF), no data read

02h DTA too small for the record size specified

03h end of file (EOF), partial data read

note 1) The current block and current record fields are set to agree with the

random record field. Then the record addressed by these fields is read

into memory at the current Disk Transfer Address.

2) The current file pointers are NOT incremented this function.

3) If the DTA is larger than the file, the file is padded to the requested

length with zeroes.

Function 22h Random Write to File Specified by FCB (FCB)

Writes one record as specified in the FCB to the current DTA

entry AH 22h

DS:DX address of the opened FCB

return AL 00h successful write operation

01h disk full; no data written (write was canceled)

02h DTA too small for the record size specified (write was

canceled)

note 1) This service cannot write to read-only files.

2) The record pointed to by the Current Block (offset 0Ch) and the Current

Record (offset 20h) fields is loaded at the DTA, then the Current Block

and Current Record fields are incremented.

3) If the record size is less than a sector, the data in the DTA is written

to a buffer; the buffer is written to disk when it contains a full

sector of data, the file is closed, or a Reset Disk (function 0Dh) is

issued.

4) The current file pointers are NOT incremented this function.

5) The record is written to disk at the current DTA address as specified

by the most recent call to function 1Ah. If the size of the record and

location of the DTA are such that a segment overflow or wraparound would

occur, the error return is set to AL=02h

Function 23h Get File Size (FCB)

Searches current subdirectory for matching file, returns size in FCB

entry AH 23h

DS:DX address of an unopened FCB

return AL 00h file found

0FFh file not found

note 1) Record size field (offset 0Eh) must be set before invoking this function

2) The disk directory is searched for the matching entry. If a matching

entry is found, the random record field is set to the number of records

in the file. If the value of the Record Size field is not an even

divisor of the file size, the value set in the relative record field is

rounded up. This gives a returned value larger than the actual file size

3) This call is used by the APPEND command in DOS 3.2+

Function 24h Set Relative Record Field (FCB)

Set random record field specified by an FCB

entry AH 24h

DS:DX address of an opened FCB

return Random Record Field of FCB is set to be same as Current Block

and Current Record.

note 1) You must invoke this function before performing random file access.

2) The relative record field of FCB (offset 21h) is set to be same as the

Current Block (offset 0Ch) and Current Record (offset 20h).

3) No error codes are returned.

4) The FCB must already be opened.

Function 25h Set Interrupt Vector

Sets the address of the code DOS is to perform each time the specified

interrupt is invoked.

entry AH 25h

AL int number to reassign the handler to

DS:DX address of new interrupt vector

return none

note 1) Registers are unchanged.

2) No error codes are returned.

3) The interrupt vector table for the interrupt number specified in AL

is set to the address contained in DS:DX. Use function 35h (Get Vector)

to get the contents of the interrupt vector and save it for later use.

4) When you use function 25 to set an interrupt vector, DOS 3.2 doesn't

point the actual interrupt vector to what you requested. Instead, it

sets the interrupt vector to point to a routine inside DOS, which does

this:

1. Save old stack pointer

2. Switch to new stack pointer allocated from DOS's stack pool

3. Call your routine

4. Restore old stack pointer

The purpose for this was to avoid possible stack overflows when there

are a large number of active interrupts. IBM was concerned (this was an

IBM change, not Microsoft) that on a Token Ring network there would be

a lot of interrupts going on, and applications that hadn't allocated

very much stack space would get clobbered.

Function 26h Create New Program Segment Prefix (PSP)

This service copies the current program-segment prefix to a new memory

location for the creation of a new program or overlay. Once the new PSP is

in place, a DOS program can read a DOS COM or overlay file into the memory

location immediately following the new PSP and pass control to it.

entry AH 26h

DX segment number for the new PSP

return none

note 1) Microsoft recommends you use the newer DOS service 4Bh (EXEC) instead.

2) The entire 100h area at location 0 in the current PSP is copied into

location 0 of the new PSP. The memory size information at location 6

in the new segment is updated and the current termination, ctrl-break,

and critical error addresses from interrupt vector table entries for

ints 22h, 23h, and 24 are saved in the new program segment starting at

0Ah. They are restored from this area when the program terminates.

3) Current PSP is copied to specified segment

Function 27h Random Block Read From File Specified by FCB

Similar to 21h (Random Read) except allows multiple files to be read.

entry AH 27h

CX number of records to be read

DS:DX address of an opened FCB

return AL 00h successful read

01h end of file, no data read

02h DTA too small for record size specified (read canceled)

03h end of file

CX actual number of records read (includes partial if AL=03h)

note 1) The record size is specified in the FCB. The service updates the Current

Block (offset 0Ch) and Current Record (offset 20h) fields to the next

record not read.

2) If CX contained 0 on entry, this is a NOP.

3) If the DTA is larger than the file, the file is padded to the requested

length with zeroes.

4) This function assumes that the FCB record size field (0Eh) is correctly

set. If not set by the user, the default is 128 bytes.

5) The record is written to disk at the current DTA address as specified

by the most recent call to function 1Ah. If the size of the record and

location of the DTA are such that a segment overflow or wraparound would

occur, the error return is set to AL=02h

Function 28h Random Block Write to File Specified in FCB

Similar to 27h (Random Write) except allows multiple files to be read.

entry AH 28h

CX number of records to write

DS:DX address of an opened FCB

return AL 00h successful write

01h disk full, no data written

02h DTA too small for record size specified (write canceled)

CX number of records written

note 1) The record size is specified in the FCB.

2) This service allocates disk clusters as required.

3) This function assumes that the FCB Record Size field (offset 0Eh) is

correctly set. If not set by the user, the default is 128 bytes.

4) The record size is specified in the FCB. The service updates the Current

Block (offset 0Ch) and Current Record (offset 20h) fields to the next

record not read.

5) The record is written to disk at the current DTA address as specified

by the most recent call to function 1Ah. If the size of the record and

location of the DTA are such that a segment overflow or wraparound would

occur, the error return is set to AL=02h

6) If called with CX=0, no records are written, but the FCB's File Size

entry (offset 1Ch) is set to the size specified by the FCB's Relative

Record field (offset 21h).

Function 29h Parse the Command Line for Filename

Parses a text string into the fields of a File Control Block

entry AH 29h

DS:SI pointer to string to parse

ES:DI pointer to memory buffer to fill with unopened FCB

AL bit mask to control parsing

bit 0 = 0: parsing stops if file seperator found

1: causes service to scan past leading chars such as

blanks. Otherwise assumes the filename begins in

the first byte

1 = 0: drive number in FCB set to default (0) if string

contains no drive number

1: drive number in FCB not changed

2 = 0: filename in FCB set to 8 blanks if no filename in

string

1: filename in FCB not changed if string does not

contain a filename

3 = 0: extension in FCB set to 3 blanks if no extension in

string

1: extension left unchanged

4-7 must be zero

return AL 00h no wildcards in name or extension

01h wildcards appeared in name or extension

0FFh invalid drive specifier

DS:SI pointer to the first byte after the parsed string

ES:DI pointer to a buffer filled with the unopened FCB

note 1) If the * wildcard characters are found in the command line, this service

will replace all subsequent chars in the FCB with question marks.

2) This service uses the characters as filename separators

DOS 1 : ; . , + / [ ] = " TAB SPACE

DOS 2,3 : ; . , + = TAB SPACE

3) This service uses the characters

: ; . , + < > | / \ [ ] = " TAB SPACE

or any control characters as valid filename separators

4) A filename cannot contain a filename terminator. If one is encountered,

all processing stops. The handle functions will allow use of some of

these characters.

5) If no valid filename was found on the command line, ES:DI +1 points

to a blank (ASCII 32).

6) This function cannot be used with filespecs which include a path

7) Parsing is in the form D:FILENAME.EXT. If one is found, a corresponding

unopened FCB is built at ES:DI

Function 2Ah Get Date

Returns day of the week, year, month, and date

entry AH 2Ah

return CX year (1980-2099)

DH month (1-12)

DL day (1-31)

AL weekday 00h Sunday

01h Monday

02h Tuesday

03h Wednesday

04h Thursday

05h Friday

06h Saturday

note 1) Date is adjusted automatically if clock rolls over to the next day,

and takes leap years and number of days in each month into account.

2) Although DOS cannot set an invalid date, it can read one, such as

1/32/80, etc.

3) DesQview also accepts CX = 4445h and DX = 5351h, i.e. 'DESQ' as valid

4) DOS will accept CH=0 (midnight) as a valid time, but if a file's time

is set to exactly midnight the time will not be displayed by the DIR

command.

Function 2Bh Set Date

set current system date

entry AH 2Bh

CX year (1980-2099)

DH month (1-12)

DL day (1-31)

return AL 00h no error (valid date)

0FFh invalid date specified

note 1) On entry, CX:DX must have a valid date in the same format as returned

by function call 2Ah

2) DOS 3.3 also sets CMOS clock

Function 2Ch Get Time

Get current system time from CLOCK$ driver

entry AH 2Ch

return CH hours (0-23)

CL minutes (0-59)

DH seconds (0-59)

DL hundredths of a second (0-99)

note 1) Time is updated every 5/100 second.

2) The date and time are in binary format

Function 2Dh Set Time

Sets current system time

entry AH 2Dh

CH hours (0-23)

CL minutes (0-59)

DH seconds (0-59)

DL hundredths of seconds (0-99)

return AL 00h if no error

0FFh if bad value sent to routine

note 1) DOS 3.3 also sets CMOS clock

2) CX and DX must contain a valid time in binary

Function 2Eh Set/Reset Verify Switch

Set verify flag

entry AH 2Eh

AL 00 to turn verify off (default)

01 to turn verify on

return none

note 1) This is the call invoked by the DOS VERIFY command

2) Setting of the verify switch can be obtained by calling call 54h

3) This call is not supported on network drives

4) DOS checks this flag each time it accesses a disk

Function 2Fh Get Disk Transfer Address (DTA)

Returns current disk transfer address used by all DOS read/write operations

entry AH 2Fh

return ES:BX address of DTA

note 1) The DTA is set by function call 1Ah

2) Default DTA address is a 128 byte buffer at offset 80h in that program's

Program Segment Prefix

Function 30h Get DOS Version Number

Return DOS version and/or user number

entry AH 30h

return AH minor version number (i.e., DOS 2.10 returns AX = 0A02h)

AL major version number

BH OEM ID number

00h IBM

16h DEC (others not known)

BL:CX 24-bit user serial number

note 1) If AL returns a major version number of zero, the DOS version is

below 1.28 for MSDOS and below 2.00 for PCDOS.

2) IBM PC-DOS always returns 0000h in BX and CX.

3) OS/2 v1.0 Compatibility Box returns a value of 10 for major version.

4) Due to the OS/2 return and the fact that some European versions of DOS

carry higher version numbers than IBM's DOS, utilities which check

for a DOS version should not abort if a higher version than required

is found unless some specific problems are known.

Function 31h Terminate Process and Stay Resident

KEEP, or TSR

entry AH 31h

AL exit code

DX program memory requirement in 16 byte paragraphs

return AX return code (retrieveable by function 4Dh)

note 1) Files opened by the application are not closed when this call is made

2) Memory can be used more efficiently if the block containing the copy of

the DOS environment is deallocated before terminating. This can be done

by loading ES with the segment contained in 2Ch of the PSP and issuing

function call 49h (Free Allocated Memory).

3) Unlike int 27h, more than 64k may be made resident with this call

Function 32h Read DOS Disk Block

* Retrieve the pointer to the drive parameter block for a drive

entry AH 32h

DL drive (0=default, 1=A:, etc.).

return AL 00h if drive is valid

0FFh if drive is not valid

DS:BX pointer to DOS Drive Parameter Table. Format of block:

Bytes Type Value

00h byte Drive: 0=A:, 1=B:, etc.

01h byte Unit within drive (0, 1, 2, etc.)

02h-03h word Bytes per sector

04h byte Sectors per cluster - 1

05h byte Cluster to sector shift (i.e., how far to shift-

left the bytes/sector to get bytes/cluster)

06h-07h word Number of reserved (boot) sectors

08h byte Number of FATs

09h-0Ah word Number of root directory entries

0Bh-0Ch word Sector # of 1st data. Should be same as # of

sectors/track.

0Dh-0Eh word # of clusters + 1 (=last cluster #)

0Fh byte Sectors for FAT

10h-11h word First sector of root directory

12h-15h dword Address of device driver header for this drive

16h byte Media Descriptor Byte for this drive

17h byte 0FFh indicates block must be rebuilt

(DOS 3.x) 00h indicates block device has

been accessed

18h-1Bh dword address of next DOS Disk Block (0FFFFh means

last in chain)

22h byte Current Working Directory (2.0 only) (64 bytes)

note 1) Use [BX+0D] to find no. of clusters (>1000H, 16-bit FAT; if not, 12-bit

(exact dividing line is probably a little below 1000h to allow for

bad sectors, EOF markers, etc.)

2) Short article by C.Petzold, PC Magazine Vol.5,no.8, and the article

"Finding Disk Parameters" in the May 1986 issue of PC Tech Journal.

3) This call is mostly supported in OS/2 1.0's DOS Compatibility Box. The

dword at 12h will not return the address of the next device driver when

in the Compatibility Box.

4) used by CHKDSK

Function 33h Control-Break Check

Get or set control-break checking at CON

entry AH 33h

AL 00h to test for break checking

01h to set break checking

DL 00h to disable break checking

01h to enable break checking

02h internal, called by PRINT.COM (DOS 3.1)

03h unknown

04h unknown

05h boot drive (DOS 4.0+)

return DL 00h if break=off

01h if break=on

(if AL=05h) boot drive, A=1, B=2, etc)

AL 0FFh error

Function 34h Return INDOS Flag

* Returns ES:BX pointing to Critical Section Flag, byte indicating whether

it is safe to interrupt DOS.

entry AH 34h

return ES:BX points to DOS "critical section flag"

note 1) If byte is 0, it is safe to interrupt DOS. This was mentioned in some

documentation by Microsoft on a TSR standard, and PC Magazine reports

it functions reliably under DOS versions 2.0 through 3.3. Chris

Dunford (of CED fame) and a number of anonymous messages on the BBSs

indicate it may not be totally reliable.

2) The byte at ES:BX+1 is used by the Print program for this same purpose,

so it's probably safer to check the WORD at ES:BX.

3) Reportedly, examination of DOS 2.10 code in this area indicates that the

byte immediately following this "critical section flag" must be 00h to

permit the PRINT.COM interrupt to be called. For DOS 3.0 and 3.1 (except

Compaq DOS 3.0), the byte before the "critical section flag" must be

zero; for Compaq DOS 3.0, the byte 01AAh before it must be zero.

4) In DOS 3.10 this reportedly changed to word value, with preceding byte.

5) This call is supported in OS/2 1.0's DOS Compatibility Box

6) Gordon Letwin of Microsoft discussed this call on ARPAnet in 1984. He

stated:

a) this is not supported under any version of the DOS

b) it usually works under DOS 2, but there may be circumstances

when it doesn't (general disclaimer, don't know of a specific

circumstance)

c) it will usually not work under DOS 3 and DOS 3.1; the DOS is

considerably restructured and this flag takes on additional

meanings and uses

d) it will fail catastrophically under DOS 4.0 and forward.

Obviously this information is incorrect since the call works fine

through DOS 3.3. Microsoft glasnost?

Function 35h Get Vector

Get interrupt vector

entry AH 35h

AL interrupt number (hexadecimal)

return ES:BX address of interrupt vector

note Use function call 25h to set the interrupt vectors

Function 36h Get Disk Free Space

get information on specified drive

entry AH 36h

DL drive number (0=default, 1=A:, 2=B:, etc)

return AX number of sectors per cluster

0FFFFh means drive specified in DL is invalid

BX number of availible clusters

CX bytes per sector

DX clusters per drive

note 1) Mult AX * CX * BX for free space on disk

2) Mult AX * CX * DX for total disk space

3) Function 36h returns an incorrect value after an ASSIGN command. Prior

to ASSIGN, the DX register contains 0943h on return, which is the free

space in clusters on the HC diskette. After ASSIGN, even with no

parameters, 0901h is returned in the DX register; this is an incorrect

value. Similar results occur with DD diskettes on a PC-XT or a PC-AT.

This occurs only when the disk is not the default drive. Results are as

expected when the drive is the default drive. Therefore, the

circumvention is to make the desired drive the default drive prior to

issuing this function call.

4) Int 21h, function call 36h returns an incorrect value after an ASSIGN

command. Prior to ASSIGN, the DX register contains 0943h on return,

which is the free space in clusters on the HC diskette. After ASSIGN,

even with no parameters, 0901h is returned in the DX register; this is

an incorrect value. Similar results occur with DD diskettes on a PC-XT

or a PC-AT. This occurs only when the disk is not the default drive.

Results are as expected when the drive is the default drive. Therefore,

the circumvention is to make the desired drive the default drive prior

to issuing this function call.

5) This function supercedes functions 1Bh and 1Ch.

Function 37h SWITCHAR / AVAILDEV

* Get/set option marking character (is usually "/"), and device type

entry AH 37h

AL 00h read switch character (returns current character in DL)

01h set character in DL as new switch character

(DOS 2.x) 02h read device availability (as set by function AL=3) into

DL. A 0 means devices that devices must be accessed in

file I/O calls by /dev/device. A non-zero value means

that devices are accessible at every level of the

directory tree (e.g., PRN is the printer and not a file

PRN).

AL=2 to return flag in DL, AL=3 to set from DL (0 = set,

1 = not set).

(DOS 2.x) 03h get device availability, where:

DL 00h means /dev/ must precede device names

01h means /dev/ need not precede device names

return DL switch character (if AL=0 or 1)

device availability flag (if AL=2 or 3)

AL 0FFh the value in AL was not in the range 0-3.

note 1) Functions 2 & 3 appear not to be implemented for DOS 3.x.

2) It is documented on page 4.324 of the MS-DOS (version 2) Programmer's

Utility Pack (Microsoft - published by Zenith).

3) Works on all versions of IBM PC-DOS from 2.0 through 3.3.1.

4) The SWITCHAR is the character used for "switches" in DOS command

arguments (defaults to '/', as in "DIR/P"). '-' is popular to make a

system look more like UNIX; if the SWITCHAR is anything other than '/',

then '/' may be used instead of '\' for pathnames

5) Ignored by XCOPY, PKARC, LIST

6) SWITCHAR may not be set to any character used in a filename

7) In DOS 3.x you can still read the "AVAILDEV" byte with subfunction 02h

but it always returns 0FFh even if you try to change it to 0 with

subfunction 03h.

8) AVAILDEV=0 means that devices must be referenced in an imaginary

subdirectory "\dev" (similar to UNIX's /dev/*); a filename "PRN.DAT"

can be created on disk and manipulated like any other. If AVAILDEV != 0

then device names are recognized anywhere (this is the default):

"PRN.DAT" is synonymous with "PRN:".

9) These functions reportedly are not supported in the same fashion in

various implementations of DOS.

10) used by DOS 3.3 CHKDSK, BASIC, DEBUG

Function 38h Return Country Dependent Information

(PCDOS 2.0, 2.1, MSDOS 2.00 only)

entry AH 38h

AL function code (must be 0 in DOS 2.x)

DS:DX pointer to 32 byte memory buffer for returned information

return CF set on error

AX error code (02h)

BX country code

DS:DX pointer to buffer filled with country information:

bytes 0,1 date/time format

0 USA standard H:M:S M/D/Y

1 European standard H:M:S D/M/Y

2 Japanese standard H:M:S D:M:Y

byte2 ASCIIZ string currency symbol

byte3 zeroes

byte4 ASCIIZ string thousands separator

byte5 zeroes

byte6 ASCIIZ string decimal separator

byte7 zeroes

bytes 8,1Fh 24 bytes reserved

Function 38h Get Country Dependent Information

(PCDOS 3.x+, MSDOS 2.01+)

entry AH 38h

AL function code

00h to get current country information

01h-0FEh country code to get information for, for countries

with codes less than 255

0FFh to get country information for countries with a code

greater than 255

BX 16 bit country code if AL=0FFh

DS:DX pointer to the memory buffer where the data will be returned

DX 0FFFFh if setting country code rather than getting info

return CF 0 (clear) function completed

1 (set) error

AX error code

02h invalid country code (no table for it)

(if DX <> 0FFFFh)

BX country code (usually international telephone code)

DS:DX pointer to country data buffer

bytes 0,1 date/time format

0 USA standard H:M:S M/D/Y

1 European standard H:M:S D/M/Y

2 Japanese standard H:M:S D:M:Y

bytes 2-6 currency symbol null terminated

byte 07h thousands separator null terminated

byte 08h zeroes

byte 09h decimal separator null terminated

byte 0Ah zeroes

byte 0Bh date separator null terminated

byte 0Ch zeroes

byte 0Dh time separator null terminated

byte 0Eh zeroes

byte 0Fh bit field currency format

bit 0 = 0 if currency symbol precedes the value

1 if currency symbol is after the value

bit 1 = 0 no spaces between value and currency symbol

1 one space between value and currency symbol

bit 2 = 1 set if currency symbol replaces decimal pt

bits 3-7 not defined by Microsoft

byte 10h number of significant decimal digits in currency

(number of places to right of decimal point)

byte 11h time format

bit 0 = 0 12 hour clock

1 24 hour clock

bits 1-7 unknown, probably not used

bytes 12h-15h address of case map routine (FAR CALL, AL = char)

entry AL ASCII code of character to be converted to

uppercase

return AL ASCII code of the uppercase input character

byte 16h data-list separator character

byte 17h zeroes

bytes 18h-21h 5 words reserved

note 1) When an alternate keyboard handler is invoked, the keyboard routine is

loaded into user memory starting at the lowest portion of availible

user memory. The BIOS interrupt vector that services the keyboard is

redirected to the memory area where the new routine resides. Each new

routine takes up about 1.6K of memory and has lookup tables that return

values unique to each language. (KEYBxx in the DOS book)

Once the keyboard interrupt vector is changed by the DOS keyboard

routine, the new routine services all calls unless the system is

returned to the US format by the ctrl-alt-F1 keystroke combination. This

does not change the interrupt vector back to the BIOS location; it

merely passes the table lookup to the ROM locations.

2) Ctrl-Alt-F1 will only change systems with US ROMS to the US layout.

Some systems are delivered with non-US keyboard handler routines in ROM

3) Case mapping call: the segment/offset of a FAR procedure that performs

country-specific lower-to-upper case mapping on ASCII characters 80h to

0FFh. It is called with the character to be mapped in AL. If there is

an uppercase code for the letter, it is returned in AL, if there is no

code or the function was called with a value of less than 80h AL is

returned unchanged.

4) This call is fully implemented in MS-DOS version 2.01 and higher. It

is in version 2.00 but not fully implemented (according to Microsoft)

Function 38h Set Country Dependent Information

entry AH 38h

AL code country code to set information for, for countries

with codes less than 255

0FFh to set country information for countries with a code

greater than 255

BX 16 bit country code if AL=0FFh

DX 0FFFFh

return CF clear successful

set if error

AX error code (02h)

Function 39h Create Subdirectory (MKDIR)

Makes a subdirectory along the indicated path

entry AH 39h

DS:DX address of ASCIIZ pathname string

return flag CF 0 successful

1 error

AX error code if any (3, 5)

note 1) The ASCIIZ string may contain drive and subdirectory.

2) Drive may be any valid drive (not nescessarily current drive)

3) The pathname cannot exceed 64 characters

Function 3Ah Remove Subdirectory (RMDIR)

entry AH 3Ah

DS:DX address of ASCIIZ pathname string

return CF clear successful

set AX error code if any (3, 5, 16)

note 1) The ASCIIZ string may contain drive and subdirectory.

2) Drive may be any valid drive (not nescessarily current drive)

3) The pathname cannot exceed 64 characters

Function 3Bh Change Current Directory (CHDIR)

entry AH 3Bh

DS:DX address of ASCIIZ string

return flag CF 0 successful

1 error

AX error code if any (3)

note 1) The pathname cannot exceed 64 characters

2) The ASCIIZ string may contain drive and subdirectory.

3) Drive may be any valid drive (not nescessarily current drive)

Function 3Ch Create A File (CREAT)

Create a file with handle

entry AH 3Ch

CX attributes for file

00h normal

01h read only

02h hidden

03h system

DS:DX address of ASCIIZ filename string

return flag CF 0 successful creation

1 error

AX 16 bit file handle

or error code (3, 4, 5)

note 1) The ASCIIZ string may contain drive and subdirectory.

2) Drive may be any valid drive (not nescessarily current drive)

3) If the volume label or subdirectory bits are set in CX, they are ignored

4) The file is opened in read/write mode

5) If the file does not exist, it is created. If one of the same name

exists, it is truncated to a length of 0.

6) Good practice is to attempt to open a file with fn 3Dh and jump to an

error routine if successful, create file if 3Dh fails. That way an

existing file will not be truncated and overwritten.

Function 3Dh Open A File

Open disk file with handle

entry AH 3Dh

AL access code byte

(DOS 2.x) bits 0-2 file attribute

000 read only

001 write only

010 read/write

bits 3-7 should be set to zero

(DOS 3.x) bits 0-2 file attribute

000 read only

001 write only

010 read/write

bit 3 reserved

0 should be set to zero

bits 4-6 sharing mode (network)

000 compatibility mode (the way FCBs open files)

001 read/write access denied (exclusive)

010 write access denied

011 read access denied

100 full access permitted

bit 7 inheritance flag

0 file inherited by child process

1 file private to child process

DS:DX address of ASCIIZ pathname string

return flag CF set on error

AX error code

1 error

AX 16 bit file handle

or error code (1, 2, 4, 5, 0Ch)

note 1) Opens any normal, system, or hidden file

2) Files that end in a colon are not opened

3) The rear/write pointer is set at the first byte of the file and the

record size of the file is 1 byte (the read/write pointer can be changed

through function call 42h). The returned file handle must be used for

all subsequent input and output to the file.

4) If the file handle was inherited from a parent process or was

duplicated by DUP or FORCEDUP, all sharing and access restrictions are

also inherited.

5) A file sharing error (error 1) causes an int 24h to execute with an

error code of 2

Function 3Eh Close A File Handle

Close a file and release handle for reuse

entry AH 3Eh

BX file handle

return flag CF 0 successful close

1 error

AX error code if error (6)

note 1) When executed, the file is closed, the directory is updated, and all

buffers for that file are flushed. If the file was changed, the time

and date stamps are changed to current

2) If called with the handle 00000, it will close STDIN (normally the

keyboard).

Function 3Fh Read From A File Or Device

Read from file with handle

entry AH 3Fh

BX file handle

CX number of bytes to read

DS:DX address of buffer

return flag CF 0 successful read

1 error

AX 0 pointer was already at end of file

or number of bytes read

or error code (5, 6)

note 1) This function attempts to transfer the number of bytes specified in CX

to a buffer location. It is not guaranteed that all bytes will be read.

If AX < CX a partial record was read.

2) If performed from STDIN (file handle 0000), the input can be redirected

3) If used to read the keyboard, it will only read to the first CR

4) The file pointer is incremented to the last byte read.

Function 40h Write To A File Or Device

Write to file with handle

entry AH 40h

BX file handle

CX number of bytes to write

DS:DX address of buffer

return flag CF 0 successful write

1 error

AX number of bytes written

or error code (5, 6)

note 1) This call attempts to transfer the number of bytes indicated in CX

from a buffer to a file. If CX and AX do not match after the write,

an error has taken place; however no error code will be returned for

this problem. This is usually caused by a full disk.

2) If the write is performed to STDOUT (handle 0001), it may be redirected

3) To truncate the file at the current position of the file pointer, set

the number of bytes in CX to zero before calling int 21h. The pointer

can be moved to any desired position with function 42h.

4) This function will not write to a file or device marked read-only.

5) May also be used to display strings to CON instead of fn 09h. This

function will write CX bytes and stop; fn 09h will continue to write

until a $ character is found.

6) This is the call that DOS actually uses to write to the screen in DOS

2.x and above.

Function 41h Delete A File From A Specified Subdirectory (UNLINK)

entry AH 41h

DS:DX pointer to ASCIIZ filespec to delete

return CF 0 successful

1 error

AX error code if any (2, 5)

note 1) This function will not work on a file marked read-only

2) Wildcards are not accepted

Function 42h Move a File Read/Write Pointer (LSEEK)

entry AH 42h

AL method code

00h offset from beginning of file

01h offset from present location

02h offset from end of file

BX file handle

CX most significant half of offset

DX least significant half of offset

return AX low offset of new file pointer

DX high offset of new file pointer

CF 0 successful move

1 error

AX error code (1, 6)

note 1) If pointer is at end of file, reflects file size in bytes.

2) The value in DX:AX is the absolute 32 bit byte offset from the beginning

of the file

Function 43h Get/Set file attributes (CHMOD)

entry AH 43h

AL 00h get file attributes

01h set file attributes

CX file attributes to set

bit 0 read only

1 hidden file

2 system file

3 volume label

4 subdirectory

5 written since backup

DS:DX pointer to full ASCIIZ file name

return CF set if error

AX error code (1, 2, 3, 5)

CX file attributes on get

attributes:

01h read only

02h hidden

04h system

0FFh archive

note 1) This call will not change the volume label or directory bits

Function 44h I/O Control for Devices (IOCTL)

Get or Set Device Information

entry AH 44h

AL 00h Get Device Information (from DX)

BX file or device handle

return DX device info

If bit 7 set: (character device)

bit 0: console input device

1: console output device

2: NUL device

3: CLOCK$ device

4: device is special

5: binary (raw) mode

6: not EOF

12: network device (DOS 3.x)

14: can process IOCTL control

strings (func 2-5)

If bit 7 clear: (file)

bits 0-5: block device number

6: file has not been written

12: Network device (DOS 3.x)

15: file is remote (DOS 3.x)

01h Set Device Information (DH must be zero for this call)

DX bits:

0 1 console input device

1 1 console output device

2 1 null device

3 1 clock device

4 1 reserved

5 0 binary mode - don't check for control chars

1 cooked mode - check for control chars

6 0 EOF - End Of File on input

7 device is character device if set, if not, EOF

is 0 if channel has been written, bits 0-5 are

block device number

12 network device

14 1 can process control strings (AL 2-5, can only be

read, cannot be set)

15 n reserved

02h Read CX bytes to device in DS:DX from BX control chan

03h Write Device Control String

BX device handle

CX number of bytes to write

DS:DX pointer to buffer

return AX number of bytes written

04h Read From Block Device (drive number in BL)

BL drive number (0=default)

CX number of bytes to read

DS:DX pointer to buffer

return AX number of bytes read

05h Write to Block Device (drive number in BL)

AX number of bytes transfered

06h Get Input Handle Status

BX file or device handle

return AL 0FFh device ready

00h device not ready

07h Get Output Handle Status

return AL 00h not ready

0FFh ready

note: for DOS 2.x, files are always ready for output

08h Removable Media Bit (DOS 3.x+)

return AX 00h device is removable

01h device is nonremovable

0Fh invalid drive specification

09h Test whether Local or Network Device in BL (DOS 3.x+)

BL drive number (0=default)

return DX attribute word, bit 12 set if device is

remote

0Ah Is Handle in BX Local or Remote? (DOS 3.x+)

BX file handle

return DX (attribute word) bit 15 set if file is remote

0Bh Change Sharing Retry Count to DX (default=3), (DOS 3.x+)

CX delay (default=1)

DX retry count (default=3)

0Ch General IOCTL (DOS 3.3 [3.2?]) allows a device driver to

prepare, select, refresh, and query Code Pages

0Dh Block Device Request (DOS 3.3+)

BL drive number (0=default)

CH major subfunction

CL minor subfunction

40h set device parameters

41h write logical device track

42h format and verify logical device track

60h get device parameters

61h read logical device track

62h verify logical device track

DS:DX pointer to parameter block

0Eh Get Logical Device (DOS 3.3+)

BL drive number (0=default)

return AL=0 block device has only one logical drive

assigned 1..n the last letter used to reference

the device (1=A:,etc)

0Fh Set Logical Device (DOS 3.3+)

BL drive number: 0=default, 1=A:, 2=B:, etc.

BX file handle

CX number of bytes to read or write

DS:DX data or buffer

DX data

return AX number of bytes transferred

or error code (call function 59h for extended error codes)

or status 00h not ready

0FFh ready

CF set if error

Function 45h Duplicate a File Handle (DUP)

entry AH 45h

BX file handle to duplicate

return CF clear AX duplicate handle

set AX error code (4, 6)

note 1) If you move the pointed of one handle, the pointer of the other will

also be moved.

2) The handle in BX must be open

Function 46h Force Duplicate of a Handle (FORCEDUP or CDUP)

Forces handle in CX to refer to the same file at the same

position as BX

entry AH 46h

BX existing file handle

CX new file handle

return CF clear both handles now refer to existing file

set error

AX error code (4, 6)

note 1) If CX was an open file, it is closed first

2) If you move the read/write pointer of either file, both will move

3) The handle in BX must be open

Function 47h Get Current Directory

Places full pathname of current directory/drive into a buffer

entry AH 47h

DL drive (0=default, 1=A:, etc.)

DS:SI points to 64-byte buffer area

return CF clear DS:DI pointer to ASCIIZ pathname of current directory

set AX error code (0Fh)

note String does not begin with a drive identifier or a backslash

Function 48h Allocate Memory

Allocates requested number of 16-byte paragraphs of memory

entry AH 48h

BX number of 16-byte paragraphs desired

return CF clear AX segment address of allocated space

BX maximum number paragraphs available

set AX error code (7, 8)

note BX indicates maximum memory availible only if allocation fails

Function 49h Free Allocated Memory

Frees specified memory blocks

entry AH 49h

ES segment address of area to be freed

return CF clear successful

set AX error code (7, 9)

note 1) This call is only valid when freeing memory obtained by function 48h.

2) A program should not try to release memory not belonging to it.

Function 4Ah Modify Allocated Memory Blocks (SETBLOCK)

Expand or shrink memory for a program

entry AH 4AH

BX new size in 16 byte paragraphs

ES segment address of block to change

return CF clear nothing

set AX error code (7, 8, 9)

or BX max number paragraphs available

note 1) Max number paragraphs availible is returned only if the call fails

2) Memory can be expanded only if there is memory availible

Function 4Bh Load or Execute a Program (EXEC)

entry AH 4Bh

AL 00h load and execute program. A PSP is built for the program

the ctrl-break and terminate addresses are set to the

new PSP.

*01h load but don't execute (note 1)

*01h load but don't execute (internal, DOS 3.x & DESQview)

*02h load but do not execute (internal, DOS 2.x only)

03h load overlay (do not create PSP, do not begin execution)

DS:DX points to the ASCIIZ string with the drive, path, and filename

to be loaded

ES:BX points to a parameter block for the load

(AL=00h) word segment address of environment string to be

passed

dword pointer to the command line to be placed at

PSP+80h

dword pointer to default FCB to be passed at PSP+5Ch

dword pointer to default FCB to be passed at PSP+6Ch

(*AL=01h) word segment of environment (0 = use current)

dword pointer to command line

dword pointer to FCB 1

dword pointer to FCB 2

dword will hold SS:SP on return

dword will hold program entry point (CS:IP) on return

(*AL=02h) word segment of environment (0 = use current)

dword pointer to command line

dword pointer to FCB 1

dword pointer to FCB 2

(AL=03h) word segment address where file will be loaded

word relocation factor to be applied to the image

return CF set error

AX error code (1, 2, 8, 0Ah, 0Bh)

note 1) If you make this call with AL=1 the program will be loaded as if you

made the call with AL=0 except that the program will not be executed.

Additionally, with AL=1 the stack segment and pointer along with the

program's CS:IP entry point are returned to the program which made the

4B01h call. These values are put in the four words at ES:BX+0Eh. On

entry to the call ES:BX points to the environment address, the command

line and the two default FCBs. This form of EXEC is used by DEBUG.COM.

2) Application programs may invoke a secondary copy of the command

processor (normally COMMAND.COM) by using the EXEC function. Your

program may pass a DOS command as a parameter that the secondary

command processor will execute as though it had been entered from the

standard input device.

The procedure is:

A. Assure that adequate free memory (17k for 2.x and 3.0, 23k for 3.1

up) exists to contain the second copy of the command processor and

the command it is to execute. This is accomplished by executing

function call 4Ah to shrink memory allocated to that of your current

requirements. Next, execute function call 48h with BX=0FFFFh. This

returns the amount of memory availible.

B. Build a parameter string for the secondary command processor in the

form:

1 byte length of parameter string

xx bytes parameter string

1 byte 0Dh (carriage return)

For example, the assembly language statement below would build the

string to cause execution of the command FOO.EXE:

DB 19,"/C C:FOO",13

C. Use the EXEC function call (4Bh), function value 0 to cause execution

of the secondary copy of the command processor. (The drive,

directory, and name of the command processor can be gotten from the

COMSPEC variable in the DOS environment passed to you at PSP+2Ch.)

D. Remember to set offset 2 of the EXEC control block to point to the

string built above.

3) All open files of a process are duplicated in the newly created

process after an EXEC, except for files originally opened with the

inheritance bit set to 1.

4) The environment is a copy of the original command processor's

environment. Changes to the EXECed environment are not passed back to

the original. The environment is followed by a copy of the DS:DX

filename passed to the child process. A zero value will cause the

child process to inherit the environment of the calling process. The

segment address of the environment is placed at offset 2Ch of the

PSP of the program being invoked.

5) This function uses the same resident part of COMMAND.COM, but makes a

duplicate of the transient part.

6) How EXEC knows where to return to: Basically the vector for int 22h

holds the terminate address for the current process. When a process

gets started, the previous contents of int 22h get tucked away in the

PSP for that process, then int 22h gets modified. So if Process A

EXECs process B, while Process B is running, the vector for int 22h

holds the address to return to in Process A, while the save location in

Process B's PSP holds the address that process A will return to when

*it* terminates. When Process B terminates by one of the usual legal

means, the contents of int 22h are (surmising) shoved onto the stack,

the old terminate vector contents are copied back to int 22h vector from

Process B's PSP, then a RETF or equivalent is executed to return control

to process A.

7) To load an overlay file with 4B: first, don't de-allocate the memory

that the overlay will load into. With the other 4Bh functions, the

opposite is true--you have to free the memory first, with function 4Ah.

Second, the "segment address where the file will be loaded" (first item

in the parameter block for sub-function 03) should be a paragraph

boundary within your currently-allocated memory. Third, if the

procedures within the overlay are FAR procs (while they execute, CS will

be equal to the segment address of the overlay area), the relocation

factor should be set to zero. On the other hand, if the CS register

will be different from the overlay area's segment address, the

relocation factor should be set to represent the difference. You

determine where in memory the overlay file will load by using the

segment address mentioned above. Overlay files are .EXEs (containing

header, relocation table, and memory image).

8) When function 00h returns, all registers are changed, including the

stack. You must resore SS, SP, and any other required registers.

Function 4Ch Terminate a Process (EXIT)

Quit with ERRORLEVEL exit code

entry AH 4Ch

AL exit code in AL when called, if any, is passed to next process

return none

note 1) Control passes to DOS or calling program

2) return code from AL can be retrieved by ERRORLEVEL or function 4Dh

3) all files opened by this process are closed, buffers are flushed, and

the disk directory is updated

4) Restores Terminate vector from PSP:000Ah

Ctrl-C vector from PSP:000Eh

Critical Error vector from PSP:0012h

Function 4Dh Get Return Code of a Subprocess (WAIT)

Gets return code from functions 31h and 4Dh (ERRORLEVEL)

entry AH 4Dh

return AL exit code of subprogram (functions 31h or 4Ch)

AH circumstance which caused termination

00h normal termination

01h control-break

02h critical device error

03h terminate and stay resident (function 31h)

note The exit code is only returned once

Function 4Eh Find First Matching File (FIND FIRST)

entry AH 4Eh

CX search attributes

DS:DX pointer to ASCIIZ filename (with attributes)

return CF set AX error code (2, 12h)

clear data block written at current DTA

format of block is: (info from BIX)

documented by Micro- |00h 1 byte attribute byte of search

soft as "reserved for |01h 1 byte drive letter for search

DOS' use on subsquent |02h 11 bytes the search name used

Find Next calls" |0Ch 2 bytes word value of last entry

function 4Fh |0Fh 4 bytes dword pointer to this DTA

|13h 2 bytes word directory start

| PC-DOS 3.10 (from INTERRUP.ARC)

|00h 1 byte drive letter

|01h-0Bh bytes search template

|0Ch 1 byte search attributes

| DOS 2.x (and DOS 3.x except 3.1?) (from INTERRUP.ARC)

|00h 1 byte search attributes

|01h 1 byte drive letter

|02h-0Ch bytes search template

|0Dh-0Eh 2 bytes entry count within directory

|0Fh-12h bytes reserved

|13h-14h 2 bytes cluster number of parent directory

15h 1 byte file attribute

16h 2 bytes file time

18h 2 bytes file date

1Ah 2 bytes low word of file size

1Ch 2 bytes high word of file size

1Eh 13 bytes name and extension of file found, plus

1 byte of 0s. All blanks are removed

from the name and extension, and if an

extension is present it is preceded by a

period.

note 1) Will not find volume label

2) This function does not support network operations

3) Wildcards are allowed in the filespec

4) If the attribute is zero, only ordinary files are found. If the volume

label bit is set, only volume labels will be found. Any other attribute

will return that attribute and all normal files together.

5) To look for everything except the volume label, set the hidden, system,

and subdirectory bits all to 1

Function 4Fh Find Next Matching File (FIND NEXT)

Find next ASCIIZ file

entry AH 4Fh

return CF clear data block written at current DTA

set AX error code (2, 12h)

note 1) If file found, DTA is formatted as in call 4Eh

2) Volume label searches using 4Eh/4Fh reportedly aren't 100% reliable

under DOS 2.x. The calls sometime report there's a volume label and

point to a garbage DTA, and if the volume label is the only item they

often won't find it

3) This function does not support network operations

4) Use of this call assumes that the original filespec contained wildcards

Function 50h "Used Internally by DOS" - Set PSP

* Set new Program Segment Prefix (current Process ID)

entry AH 50h

BX segment address of new PSP

return none - swaps PSP's regarded as current by DOS

note 1) By putting the PSP segment value into BX and issuing call 50h DOS stores

that value into a variable and uses that value whenever a file call is

made.

2) Note that in the PSP (or PDB) is a table of 20 (decimal) open file

handles. The table starts at offset 18h into the PSP. If there is an

0FFh in a byte then that handle is not in use. A number in one of the

bytes is an index into an internal FB table for that handle. For

instance the byte at offset 18h is for handle 0, at offset 19h handle

1, etc. up to 13h. If the high bit is set then the file associated by

the handle is not shared by child processes EXEC'd with call 4Bh.

3) Function 50h is dangerous in background operations prior to DOS 3.x as

it uses the wrong stack for saving registers. (same as functions

0..0Ch in DOS 2.x)

4) Under DOS 2.x, this function cannot be invoked inside an int 28h handler

without setting the Critical Error flag

5) Open File information, etc. is stored in the PSP DOS views as current.

If a program (eg. a resident program) creates a need for a second PSP,

then the second PSP should be set as current to make sure DOS closes

that as opposed to the first when the second application finishes.

6) See PC Mag Vol.5, No 9, p.314 for discussion.

7) Used by DOS 3.3 PRINT & DEBUG, DesQview 2.01, Windows 1.03, SYMDEB

from MASM 4.0

Function 51h "Used Internally by DOS" - Get Program Segment Prefix

* Returns the PSP address of currently executing program

entry AH 51h

return BX address of currently executing program

offset

00h program exit point

02h memory size in paragraphs

04h unused (0)

05h CP/M style entry point (far call to DOS)

0Ah terminate address (old int 22h)

0Ch terminate segment

0Eh break address (old int 23h)

10h break segment

12h error address (old int 24h)

14h error segment

16h parent PSP segment

18h DOS 2.0+ open files, 0FFh = unused

2Ch DOS 2.0+ environment segment

2Eh far ptr to process's SS:SP

32h DOS 3.x max open files

34h DOS 3.x openfile table address

36h DOS 3.x openfile table segment

38h unused by DOS versions <= 3.3

50h DOS function dispatcher (FAR routine)

53h unused

55h FCB #1 extension

5Ch FCB #1

6Ch FCB #2

80h command tail / default DTA buffer

note 1) Used in DOS 2.x, 3.x uses 62h

2) Function 51h is dangerous in background operations prior to DOS 3.x as

it uses the wrong stack for saving registers. (same as functions

0..0Ch in DOS 2.x)

3) 50h and 51h might be used if you have more than one process in a PC.

For instance if you have a resident program that needs to open a file

you could first call 51h to save the current id and then call 50h to set

the ID to your PSP.

4) Under DOS 2.x, this function cannot be invoked inside an int 28h handler

without setting the Critical Error flag

5) Used by DOS 3.3 PRINT, DEBUG

Function 52h "Used Internally by DOS" - IN-VARS

* Returns a pointer to a set of DOS data variables MCB chain,

pointer to first device driver and a pointer to disk parameter

blocks (first one)

entry AH 52h

return ES:BX pointer to the DOS list of lists, for disk information. Does not

access the disk, so information in tables might be incorrect if

disk has been changed. Returns a pointer to the following array

of longword pointers:

Bytes Value

-2h,-1h segment of first memory control block

00h-03h pointer to first DOS disk block (see function 36h)

04h-07h Pointer to list of DOS file tables

dword pointer to next file table

word number of files in this table

35h bytes per file

00h-01h number of file handles referring to

this file

02h-06h unknown

07h-0Ah pointer to device driver header if

character device; pointer to DOS Device

Control Block if block device (see

fn 32h for format)

0Bh-1Fh unknown

20h-2Ah filename in FCB format (no path, no

period, blank-padded)

2Bh-2Ch PSP segment of file's owner

2Dh-30h unknown - 0 always

31h-32h unknown

33h-34h unknown

8h-0Bh pointer to CLOCK$ device driver, whether installable or

resident

0Ch-0Fh pointer to actual CON: device driver, whether

installable or resident

(DOS 2.x)

10 number of logical drives in system

11-12 maximum bytes/block of any block device

13-16 unknown

17 beginning (not a pointer. The real beginning!) of NUL

device driver. This is the first device on DOS's linked

list of device drivers.

(DOS 3.x)

10h-11h maximum bytes/block of any block device (0200h)

12h-15h pointer to first disk buffer

16h-19h partially undefined: Pointer to array of drive info:

51h bytes per drive, starting with A: ...

00h-3Fh current path as ASCIIZ, starting with 'x:\'

40h-43h unknown zeros always

44h unknown flags? Usually 40h, except for

entry after last valid entry = 00h

45h-48h pointer to DOS disk block for this drive

49h-4Ah unknown. Current track or block?

-1 if never accessed

4Bh-4Eh unknown -1 always

4Fh-52h unknown 2 always

1Ah-1Dh pointer to FCB table (if CONFIG.SYS contains FCBS=)

1Eh-1Fh size of FCB table

20h number of block devices

21h value of LASTDRIVE command in CONFIG.SYS (default 5)

22h beginning (not a pointer. The real beginning!) of NUL

device driver. This is the first device on DOS's linked

list of device drivers.

note 1) This call is not supported in OS/2 1.0's DOS Compatibility Box

2) Used by DOS 4.0 MEM.EXE, DOS 3.3 ASSIGN.COM, PRINT.COM, SUBST.EXE

Function 53h "Used Internally by DOS" - Translate BPB

* Translates BPB (BIOS Parameter Block, see below) into a DOS Disk

Block (see function call 32h).

entry AH 53h

DS:SI pointer to BPB

ES:BP pointer to area for DOS Disk Block.

Layout of Disk Block:

bytes value

00h-01h bytes per sector, get from DDB bytes 02h-03h.

02h sectors per cluster, get from (DDB byte 4) + 1

03h-04h reserved sectors, get from DDB bytes 06h-07h

05h number of FATs, get from DDB byte 08h

06h-07h number of root dir entries, get from DDB bytes 09h-0Ah

08h-09h total number of sectors, get from:

((DDB bytes 0Dh-0Eh) - 1) * (sectors per cluster (BPB

byte 2)) + (DDB bytes 0Bh-0Ch)

0Ah media descriptor byte, get from DDB byte 16h

0Bh-0Ch number of sectors per FAT, get from DDB byte 0Fh

return unknown

Function 54h Get Verify Setting

Get verify flag status

entry AH 54h

return AL 00h if flag off

01h if flag on

note Flag can be set with function 2Eh

Function 55h "Used Internally by DOS" - Create "Child" PSP

* Create PSP: similar to function 26h (which creates a new Program

Segment Prefix at segment in DX) except creates a "child" PSP

rather than copying the existing one.

entry AH 55h

DX segment number at which to create new PSP.

return unknown

note 1) This call is similar to call 26h which creates a PSP except that unlike

call 26h the segment address of the parent process is obtained from the

current process ID rather than from the CS value on the stack (from the

INT 21h call). DX has the new PSP value and SI contains the value to be

placed into PSP:2 (top of memory).

2) Function 55 is merely a substitute for function 26h. It will copy the

current PSP to the segment address DX with the addition that SI is

assumed to hold the new memory top segment. This means that function

26h sets SI to the segment found in the current PSP and then calls

function 55h.

Function 56h Rename a File

entry AH 56h

DS:DX pointer to ASCIIZ old pathname

ES:DI pointer to ASCIIZ new pathname

return CF clear successful rename

set AX error code (2, 3, 5, 11h)

note 1) Works with files in same drive only

2) Global characters not allowed in filename

3) The name of a file is its full pathname. The file's full pathname can

be changed, while leaving the actual FILENAME.EXT unchanged. Changing

the pathname allows the file to be "moved" from subdirectory to

subdirectory on a logical drive without actually copying the file.

4) DOS 3.x allows renaming of directories

** Programmer's Technical Reference for MSDOS and the IBM PC **

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³ Shareware Version, 06/17/91 ³

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ISBN 1-878830-02-3 (disk-based text)

C H A P T E R F I V E

Interrupts 22h Through 86h

note: the registered version of this chapter is more than twice this size.

Interrupt 22h Terminate Address

(0:0088h)

This interrupt transfers control to the far (dword) address at this interrupt

location when an application program terminates. The default address for this

interrupt is 0:0088h through 0:008Bh. This address is copied into the program's

Program Segment Prefix at bytes 0Ah through 0Dh at the time the segment is

created and is restored from the PSP when the program terminates. The calling

program is normally COMMAND.COM or an application. Do not issue this interrupt

directly, as the EXEC function call does this for you. If an application

spawns a child process, it must set the Terminate Address prior to issuing the

EXEC function call, otherwise when the second program terminated it would

return to the calling program's Terminate Address rather than its own. This

address may be set with int 21, function 25h.

Interrupt 23h Ctrl-Break Exit Address

(0:008Ch)

If the user enters a Ctrl-Break during STDIN, STDOUT, STDPRN, or STDAUX, int

23h is executed. If BREAK is on, int 23h is checked on MOST function calls

(notably 06h). If the user written Ctrl-Break routine saves all registers, it

may end with a return-from-interrupt instruction (IRET) to continue program

execution. If the user-written interrupt program returns with a long return, the

carry flag is used to determine whether the program will be aborted. If the

carry flag is set, the program is aborted, otherwise execution continues (as

with a return by IRET). If the user-written Ctrl-Break interrupt uses function

calls 09h or 0Ah, (Display String or Buffered Keyboard Input) then a three-byte

string of 03h-0Dh-0Ah (ETX/CR/LF) is sent to STDOUT. If execution is continued

with an IRET, I/O continues from the start of the line. When the interrupt

occurs, all registers are set to the value they had when the original function

call to DOS was made. There are no restrictions on what the Ctrl-Break handler

is allowed to do, including DOS function calls, as long as the registers are

unchanged if an IRET is used. If the program creates a new segment and loads a

second program which itself changes the Ctrl-Break address, the termination of

the second program and return to the first causes the Ctrl-Break address to

be restored from the PSP to the value it had before execution of the second

program.

Interrupt 24h Critical Error Handler

(0:0090h)

When a critical error occurs within DOS, control is transferred to an error

handler with an int 24h. This may be the standard DOS error handler (ABORT,

RETRY, IGNORE) or a user-written routine.

On entry to the error handler, AH will have its bit 7=0 (high order bit)

if the error was a disk error (probably the most common error), bit 7=1 if

not.

BP:SI contains the address of a Device Header Control Block from which

additional information can be retrieved (see below).

The register is set up for a retry operation and an error code is in the

lower half of the DI register with the upper half undefined. These are the

error codes:

The user stack is in effect and contains the following from top to bottom:

IP DOS registers from issuing int 24h

CS int 24h

flags

AX user registers at time of signal

BX int 21h request

IP from original int 21h

flags

To reroute the critical error handler to a user-writen critical error handler,

the following should be done:

Before an int 24h occurs:

1) The user application initialization code should save the int 24h vector and

replace the vector with one pointing to the user error routine.

When the int 24h occurs:

2) When the user error routine received control it should push the flag

registers onto the stack and execute a far call to the original int 24h

vector saved in step 1.

3) DOS gives the appropriate prompt, and waits for user input (Abort, Retry,

Ignore, Fail). After the user input, DOS returns control to the user error

routine instruction following the far call.

4) The user error routine can now do any tasks nescessary. To return to the

original application at the point the error occurred, the error routine needs

to execute an IRET instruction. Otherwise, the user error routine should

remove the IP, CS, and flag registers from the stack. Control can then be

passed to the desired point.

Int 24h provides the following values in registers on entry to the interrupt

handler:

entry AH status byte (bits)

7 0 disk I/O hard error

1 other error - if block device, bad FAT

- if char device, code in DI

6 unused

5 0 if IGNORE is not allowed

1 if IGNORE is allowed

4 0 if RETRY is not allowed

1 if RETRY is allowed

3 0 if FAIL is not allowed

1 if FAIL is allowed

2 \ disk area of error 00 = DOS area 01 = FAT

1 / 10 = root dir 11 = data area

0 0 if read operation

1 if write operation

AL drive number if AH bit 7 = 1, otherwise undefined

If it is as hard error on disk (AH bit 7=0), register AL

contains the failing drive number (0=A:, 1=B:, etc.).

BP:SI address of a Device Header Control Block for which error

occurred block device if high bit of BP:SI+4 = 1

low byte of DI: error code (note: high byte is undefined)

error code description

00h attempt to write on write-protected diskette

01h unknown unit

02h drive not ready

03h unknown command

04h data error (bad CRC)

05h bad request structure length

06h seek error

07h unknown media type

08h sector not found

09h printer out of paper

0Ah write fault

0Bh read fault

0Ch general failure

0Fh invalid disk change (DOS 3.x+)

10h (DOS 3.x) FCB unavailable

11h (DOS 3.x) sharing buffer overflow

The handler must return this information:

The registers are set such that if an IRET is executed, DOS responds according

to (AL) as follows:

AL 00h ignore the error

01h retry the operation

02h terminate via int 22h

03h fail the system call that is in progress (DOS 3.x+)

note 1) Be careful when choosing to ignore a response because this causes DOS to

beleive that an operation has completed successfully when it may not

have.

2) If the error was a character device, the contents of AL are invalid.

OTHER ERRORS

If AH bit 7=1, the error occurred on a character device, or was the result of

a bad memory image of the FAT. The device header passed in BP:SI can be examined

to determine which case exists. If the attribute byte high-order bit indicates

a block device, then the error was a bad FAT. Otherwise, the error is on a

character device.

If a character device is involved, the contents of AL are unpredictable, the

error code is in DI as above.

Notes:

1. Before giving this routine control for disk errors, DOS performs several

retries. The number of retries varies according to the DOS version.

2. For disk errors, this exit is taken only for errors occurring during an

int 21h function call. It is not used for errors during an int 25h or 26h.

3. This routine is entered in a disabled state.

4. All registers must be preserved.

5. This interrupt handler should refrain from using DOS function calls. If

necessary, it may use calls 01h through 12h. Use of any other call destroys

the DOS stack and leaves DOS in an unpredictable state.

6. The interrupt handler must not change the contents of the device header.

7. If the interrupt handler handles errors itself rather than returning to DOS,

it should restore the application program's registers from the stack,

remove all but the last three words on the stack, then issue an IRET. This

will return to the program immediately after the int 21h that experienced

the error. Note that if this is done DOS will be in an unstable state until

a function call higher than 12h is issued, therefore not recommended.

8. For DOS 3.x, IGNORE requests (AL=0) are converted to FAIL for critical

errors that occur on FAT or DIR sectors.

9. For DOS 3.10 up, IGNORE requests (AL=0) are converted to FAIL requests

for network critical errors (50-79).

The device header pointed to by BP:SI is as follows:

DWORD Pointer to next device (0FFFFh if last device)

WORD Attributes:

Bit 15 1 if character device.

If bit 15 is 1:

Bit 0 = 1 if current standard input

Bit 1 = 1 if current standard output

Bit 2 = 1 if current NULL device

Bit 3 = 1 if current CLOCK device

0 if block device

Bit 14 is the IOCTL bit

WORD pointer to device driver strategy entry point

WORD pointer to device driver interrupt entry point

8-BYTE character device named field for block devices. The first byte is the

number of units.

To tell if the error occurred on a block or character device, look at bit 15

in the attribute field (WORD at BP:SI+4).

If the name of the character device is desired, look at the eight bytes

starting at BP:SI+10.

HANDLING OF INVALID RESPONSES (DOS 3.x)

A) If IGNORE (AL=0) is specified by the user and IGNORE is not allowed

(bit 5=0), make the response FAIL (AL=3).

B) If RETRY (AL=1) is specified by the user and RETRY is not allowed

(bit 4=0), make the response FAIL (AL=3).

C) If FAIL (AL=3) is specified by the user and FAIL is not allowed (bit

3=0), make the response ABORT. (AL=2)

Interrupt 25h Absolute Disk Read

Interrupt 26h Absolute Disk Write

(0:0094h, 0:0098h)

These transfer control directly to the device driver. On return, the original

flags are still on the stack (put there by the INT instruction). This is

necessary because return information is passed back in the current flags.

The number of sectors specified is transferred between the given drive and the

transfer address. Logical sector numbers are obtained by numbering each sector

sequentially starting from track 0, head 0, sector 1 (logical sector 0) and

continuing along the same head, then to the next head until the last sector on

the last head of the track is counted. Thus, logical sector 1 is track 0, head

0, sector 2; logical sector 2 is track 0, head 0, sector 3; and so on. Numbering

then continues wih sector 1 on head 0 of the next track. Note that although the

sectors are sequentially numbered (for example, sectors 2 and 3 on track 0 in

the example above), they may not be physically adjacent on disk, due to

interleaving. Note that the mapping is different from that used by DOS 1.10 for

dual-sided diskettes.

The request is as follows:

int 25 for Absolute Disk Read,

int 26 for Absolute Disk Write

entry AL drive number (0=A:, 1=B:, etc)

CX number of sectors to read

DS:BX disk transfer address (buffer)

DX first relative sector to read - beginning logical sector number

return CF set if error

AL error code issued to int 24h in low half of DI

AH 01h bad command

02h bad address mark

03h write-protected disk

04h requested sector not found

08h DMA failure

10h data error (bad CRC)

20h controller failed

40h seek operation failed

80h attachment failed to respond

note 1) Original flags on stack! Be sure to pop the stack to prevent

uncontrolled growth

2) Ints 25 and 26 will try rereading a disk if they get an error the first

time.

3) All registers except the segment registers are destroyed by these calls

Interrupt 25h ABSOLUTE DISK READ

(except DOS 4.0/Compaq DOS 3.31 >32M partition)

entry AL drive number (0=A, 1=B, etc)

DS:BX pointer to Disk Transfer Address (buffer)

CX number of sectors to read

DX first relative sector to read

return CF 1 if error

AL error code issued to int 24h in low half of DI

AH 80h attachment failed to respond

40h seek operation failed

20h controller failed

10h data error (bad CRC)

08h DMA failure

04h requested sector not found

03h write-protected disk

02h bad address mark

01h bad command

note Original flags on stack!

Interrupt 25h DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK READ

(>32M hard-disk partition)

entry AL drive number (0=A, 1=B, etc)

CX 0FFFFh

DS:BX Packet address

DWORD sector number

WORD number of sectors to read

DWORD transfer address

return same as above?

note Partition is potentially >32Mb (and requires this form of the call) if

bit 1 of device attribute word in device driver is set

Interrupt 26h ABSOLUTE DISK WRITE

(except DOS 4.0/Compaq DOS 3.31 >32M partition)

entry AL drive number (0=A, 1=B, etc)

DS:BX pointer to Disk Transfer Address (buffer)

CX number of sectors to write

DX first relative sector to write

return CF 1 if error

AL error code issued to int 24h in low half of DI

AH same error codes as for int 25h

note Original flags on stack!

Interrupt 26h DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK WRITE

(>32M hard disk partitions)

entry AL drive number (0=A, 1=B, etc)

CX 0FFFFh

DS:BX Packet address

DWORD sector number

WORD number of sectors to write

DWORD transfer address

return same as above?

note Partition is potentially >32M (and requires this form of the call) if

bit 1 of device attribute word in device driver is set

Interrupt 27h Terminate And Stay Resident

(0:009Ch) (obsolete)

This vector is used by programs that are to remain resident when COMMAND.COM

regains control.

After initializing itself, the program must set DX to its last address plus

one relative to the program's initial DS or ES value (the offset at which other

programs can be loaded), then execute interrupt 27h. DOS then considers the

program as an extension of itself, so the program is not overlaid when other

programs are executed. This is useful for loading programs such as utilities

and interrupt handlers that must remain resident.

entry CS current program segment

DX last program byte + 1

return none

note 1) This interrupt must not be used by .EXE programs that are loaded into

the high end of memory.

2) This interrupt restores the interrupt 22h, 23h, and 24h vectors in the

same manner as interrupt 20h. Therefore, it cannot be used to install

permanently resident Ctrl-Break or critical error handler routines.

3) The maximum size of memory that can be made resident by this method is

64K.

4) Memory can be more efficiently used if the block containing a copy of

the environment is deallocated before terminating. This can be done by

loading ES with the segment contained in 2Ch of the PSP, and issuing

function call 49h (Free Allocated Memory).

5) DOS function call 4Ch allows a program to pass a completion code to DOS,

which can be interpreted with processing (see function call 31h).

6) Terminate and stay resident programs do not close files.

7) Int 21, function 31h is the preferred method to cause a program to

remain resident because this allows return information to be passed and

allows a program larger than 64K to remain resident.

Interrupt 28h (not documented by Microsoft)

* DOS Idle Interrupt

Int 28h has been provided by DOS since release 2.0. The int 28h process is

similar to the "Timer Tick" process provided by BIOS via int 1Ch in that it is

an "outbound" (from DOS) call which an application can "hook onto" to get

service at a particular entry point. DOS normally only issues int 28h when it

recieves a function call (int 21h) from a foreground application with an

argument in the range of 0 thru 12 (0Ch) in the AH register, or when it is

idling waiting for keyboard input. In effect, when DOS issues int 28h, it is

saying to the background task "I'm not doing anything hot right now, if you can

use the time, go ahead." This means that a foreground application which doesn't

do many low-number DOS functions can preempt CPU time easily.

It is possible, if you are careful, to enhance the background priority by

providing more int 28h calls than DOS normally would issue.

When int 28h is being issued it is usually safe to do DOS calls. You won't get

int 28hs if a program is running that doesn't do its keyboard input through

DOS. You should rely on the timer interrupt for these.

It is used primarily by the PRINT.COM routines, but any number of other

routines can be chained to it by saving the original vector and calling it with

a FAR call (or just JMPing to it) at the end of the new routine.

Int 28h is not called at all when any non-trivial foreground task is running.

As soon as a foreground program has a file open, int 28h no longer gets called.

Could make a good driver for for a background program that works as long as

there is nothing else going on in the machine.

DOS uses 3 separate internal stacks: one for calls 01h through 0Ch; another

for calls 0Dh and above; and a third for calls 01h through 0Ch when a Critical

Error is in progress. When int 28h is called, any calls above 0Ch can be

executed without destroying the internal stack used by DOS at the time.

The byte which is pushed on the stack before an int 28h just indicates which

stack area is being used by the current int 21h call. In DOS 3.1, the code

sequence that calls int 28h looks like this:

PUSH SS:[0304]

INT 28

POP SS:[0304]

The low-order byte of the word pushed contains 1 if the int 21h call currently

in progress is for services 1 through 0Ch, and 0 for service 0 and for 0Dh and

up. Assuming that the last DOS call was not a reentrant one, this tells you

which set of DOS services should be safe to call.

If the InDOS flag is zero on int 28h, then it was called by someone other than

DOS, and the word on the stack should NOT be examined.

entry no parameters availible

return none

note 1) The int 28h handler may invoke any int 21h function except functions

00h through 0Ch (and 50h/51h under DOS 2.x unless DOS CritErr flag is

set).

2) Apparently int 28h is also called during screen writes

3) Until some program installs its own routine, this interrupt vector

simply points to an IRET opcode.

4) Supported in OS/2 1.0's DOS Compatibility Box

Interrupt 29h (not documented by Microsoft)

* Internal - Quick Screen Output

This method is extremely fast (much faster than DOS 21h subfunctions 2 and 9,

for example), and it is portable, even to "non-compatible" MS-DOS computers.

entry AL character to output to screen

return unknown

note 1) Documented by Digital Research's DOS Reference as provided with the

DEC Rainbow

2) If ANSI.SYS is installed, character output is filtered through it.

3) Works on the IBM PC and compatibles, Wang PC, HP-150 and Vectra, DEC

Rainbow, NEC APC, Texas Instruments PC and others

4) This interrupt is called from the DOS's output routines if output is

going to a device rather than a file, and the device driver's attribute

word has bit 3 (04h) set to "1".

5) This call has been tested with MSDOS 2.11, PCDOS 2.1, PCDOS 3.1, PCDOS

3.2, and PCDOS 3.3.

6) Used in IBMBIO.COM as a vector to int 10, function 0Eh (write TTY)

followed by an IRET.

Interrupt 2Ah Microsoft Networks - Session Layer Interrupt

* (not documented by Microsoft)

entry AH 00h check to see if network BIOS installed

return AH <> 0 if installed

01h execute NETBIOS request

02h set net printer mode

03h get shared-device status (check direct I/O)

AL 00h

DS:SI pointer to ASCIIZ disk device name

return CF 0 if allowed

04h execute NETBIOS

AL 0 for error retry

1 for no retry

ES:BX pointer to network control block

return AX 0 for no error

AH 1 if error

AL error code

05h get network resource information

AL 00h

return AX reserved

BX number of network names

CX number of commands

DX number of sessions

06h Network Print-stream Control

note NETBIOS 1.10

20h unknown

note AL=01h intercepted by DESQview 2.0

80h Begin DOS Critical Section

AL 1 to 6

81h End DOS Critical Section

AL 1 to 6

82h Server Hook

return unknown

note called by the int 21h function dispatcher

in DOS 3.10+ for function 0 and functions

greater than 0Ch except 59h

84h keyboard busy loop

note similar to DOS's int 28h

Interrupt 2Bh (not documented by Microsoft)

* Unknown - Internal Routine for DOS (IRET)

Interrupt 2Ch (not documented by Microsoft)

* Unknown - Internal Routine for DOS (IRET)

Interrupt 2Dh (not documented by Microsoft)

* Unknown - Internal Routine for DOS (IRET)

Interrupt 2Eh (undocumented by Microsoft) (DOS 2.0+)

* Internal Routine for DOS (Alternate EXEC)

This interrupt passes a command line addressed by DS:SI to COMMAND.COM. The

command line must be formatted just like the unformatted parameter area of a

Program Segment Prefix. That is, the first byte must be a count of characters,

and the second and subsequent bytes must be a command line with parameters,

terminated by a carriage return character.

When executed, int 2Eh will reload the transient part of the command

interpreter if it is not currently in memory. If called from a program that

was called from a batch file, it will abort the batch file. If executed from a

program which has been spawned by the EXEC function, it will abort the whole

chain and probably lock up the computer. Int 2Eh also destroys all registers

including the stack pointer.

Int 2Eh is called from the transient portion of the program to reset the DOS

PSP pointers using the above Functions #81 & #80, and then reenters the

resident program.

When called with a valid command line, the command will be carried out by

COMMAND.COM just as though you had typed it in at the DOS prompt. Note that the

count does not include the carriage return. This is an elegant way to perform a

SET from an application program against the master environment block for

example.

entry DS:SI pointer to an ASCIIZ command line in the form:

count byte

ASCII string

carriage return

null byte

note 1) Destroys all registers including stack pointer

2) Seems to work OK in both DOS 2.x and 3.x

3) It is reportedly not used by DOS.

4) As far as known, int 2Eh is not used by DOS 3.1, although it was called

by COMMAND.COM of PCDOS 3.0, so it appears to be in 3.1 only for the

sake of compatibility.

Interrupt 2Fh Multiplex Interrupt

Interrupt 2Fh is the multiplex interrupt. A general interface is defined

between two processes. It is up to the specific application using interrupt

2Fh to define specific functions and parameters.

This interrupt is becoming more commonly used as the availible interrupt 21

functions are getting to be in short supply. Int 2Fh doesn't require any

support from DOS itself for it to be used in application programs. It's not

handled by DOS, but by the programs themselves.

Every multiplex interrupt handler is assigned a specific multiplex number.

The multiplex number is specified in the AH register; the AH value tells which

program your request is directed toward. The specific function that the handler

is to perform is placed in the AL register. Other parameters are places in the

other registers as needed. The handlers are chained into the 2Fh interrupt

vector and the multiplex number is checked to see if any other application is

using the same multiplex number. There is no predefined method for assigning a

multiplex number to a handler. You must just pick one. To avoid a conflict if

two applications choose the same multiplex number, the multiplex numbers used by

an application should be patchable. In order to check for a previous

installation of the current application, you can search memory for a unique

string included in your program. If the value you wanted in AH is taken but

you don't find the string, then another application has grabbed that location.

Int 2Fh was not documented under DOS 2.x. There is no reason not to use int 2Fh

as the multiplex interrupt in DOS 2.x. The only problem is that DOS 2.x does not

initialize the int 2Fh vector, so when you try to chain to it like you are

supposed to, it will crash. If your program checks the vector for being zero

and initializes it itself or doesn't chain in that case, it will work for you

n 2.x just the same as 3.x.

Function 01h PRINT.COM

Values 00h-7Fh are reserved for DOS, not that anyone cares much.

Values 0C0h-0FFh are reserved for applications.

entry AH 01h

AL 00h PRINT Get Installed State

This call must be defined by all int 2Fh handlers. It

is used by the caller of the handler to determine if

the handler is present. On entry, AL=0. On return, AL

contains the installed state as follows:

return AL 0FFh installed

01h not installed, not OK to install

00h not installed, OK to install

01h PRINT Submit File

DS:DX pointer to submit packet

format byte level

dword pointer to ASCIIZ filename

return CF set if error

AX error code

note 1) A submit packet contains the level (BYTE) and a pointer

to the ASCIIZ string (DWORD in offset:segment form).

The ASCIIZ string must contain the drive, path, and

filename of the file you want to print. The filename

cannot contain global filename characters.

return CF set if error

AX error code

02h PRINT Cancel File

On entry, AL=2 and DS:DX points to the ASCIIZ string for

the print file you want to cancel. Global filename

characters are allowed in the filename.

DS:DX pointer to ASCIIZ file name to cancel (wildcards OK)

return CF set if error

AX error code

03h PRINT remove all files

return CF set if error

AX error code

04h PRINT hold queue/get status

This call holds the jobs in the print queue so that you

can scan the queue. Issuing any other code releases the

jobs. On entry, AL=4. On return, DX contains the error

count. DS:SI points to the print queue. The print queue

consists of a series of filename entries. Each entry is

64 bytes long. The first entry in the queue is the file

currently being printed. The end of the queue is marked

by the entry having a null as the first character.

return DX error count

DS:SI pointer to print queue (null-string terminated

list of 64-byte ASCIIZ filenames)

CF set if error

AX error code

01h function invalid

02h file not found

03h path not found

04h too many open files

05h access denied

08h queue full

09h spooler busy

0Ch name too long

0Fh drive invalid

05h PRINT restart queue

return CF set if error

AX error code

Function 05h DOS 3.x critical error handler

entry AH 05h

AL 00h installation check

return AL 00h not installed, OK to install

01h not installed, can't install

0FFh installed

note This set of functions allows a user program to

partially or completely override the default

critical error handler in COMMAND.COM

AL 01h handle error - nonzero error code in AL

return CF clear

ES:DI pointer to ASCIIZ error message

CF set use default error handler

AL (?)

Function 06h ASSIGN

entry AH 06h

00h installation check

return AH <> 0 if installed

01h get memory segment

return ES segment of ASSIGN work area

Function 10h SHARE

entry AH 10h

AL 00h installation check

return AL 00h not installed, OK to install

01h not installed, not OK to install

0FFh installed

Function 11h Multiplex - network redirection

entry AH 11h

AL 00h installation check

return AL 00h not installed, OK to install

01h not installed, not OK to install

0FFh installed

01h-05h unknown

06h close remote file

07h-09h unknown

0Ah unknown

stack word (?)

return CF set on error

0Bh unknown

stack word (?)

return CF set on error(?)

0Ch unknown

0Dh unknown

0Eh unknown

stack word (?)

return (?)

0Fh-16h unknown

17h unknown

stack word (?)

return (?)

18h unknown

stack word (?)

return (?)

19h-1Dh unknown

1Eh do redirection

stack word function to execute

return CF set on error

1Fh printer setup

stack word function(?)

return CF set on error(?)

20h-25h unknown

stack word (?)

26h unknown

Function 12h multiplex, DOS 3.x internal services

entry AH 12h

AL 00h installation check

return AL 0FFh for compatibility with other

int 2Fh functions

01h close file (?)

stack word value - unknown

return BX unknown

CX unknown

ES:DI pointer to unknown value

note Can be called only from within DOS

02h get interrupt address

stack word vector number

return ES:BX pointer to interrupt vector

stack unchanged

03h get DOS data segment

return DS segment of IBMDOS.COM file

04h normalize path separator

stack word character to normalize

return AL normalized character (forward slash

turned to backslash)

stack unchanged

05h output character

stack word character to output

return stack unchanged

note Can be called only from within DOS

06h invoke critical error

return AL 0-3 for Abort, Retry, Ignore, Fail

note Can be called only from within DOS

07h move disk buffer (?)

DS:DI pointer to disk buffer

return buffer moved to end of buffer list

note Can be called only from within DOS

08h decrement word

ES:DI pointer to word to decrement

return AX new value of word

note Word pointed to by ES:DI decremented,

skipping zero

09h unknown

DS:DI pointer to disk buffer(?)

return (?)

note Can be called only from within DOS

0Ah unknown

note Can be called only from within DOS

0Bh unknown

ES:DI pointer to system file table entry(?)

return AX (?)

note Can be called only from within DOS

0Ch unknown

note Can be called only from within DOS

0Dh get date and time

return AX current date in packed format

DX current time in packed format

note Can be called only from within DOS

0Eh do something to all disk buffers (?)

return DS:DI pointer to first disk buffer

note can be called only from within DOS

0Fh unknown

DS:DI pointer to (?)

return DS:DI pointer to (?)

note 1) Can be called only from within DOS

2) Calls on function 1207h

10h find dirty/clean(?) buffer

DS:DI pointer to first disk buffer

return DS:DI pointer to first disk buffer which has

(?) flag clear

ZF clear if found

set if not found

11h normalize ASCIIZ filename

DS:SI pointer to ASCIIZ filename to normalize

ES:DI pointer to buffer for normalized filename

return destination buffer filled with uppercase

filename, with slashes turned to backslashes

12h get length of ASCIIZ string

ES:DI pointer to ASCIIZ string

return CX length of string

13h uppercase character

stack word character to convert to uppercase

return AL uppercase character

stack unchanged

14h compare far pointers

DS:SI first pointer

ES:DI second pointer

return ZF set if pointers are equal

ZF clear if not equal

15h unknown

DS:DI pointer to disk buffer

stack word (?)

return stack unchanged

note Can be called only from within DOS

16h get address of system FCB

BX system file table entry number

return ES:DI pointer to system file table entry

17h set default drive (?)

stack word drive (0=A:, 1=B:, etc)

return DS:SI pointer to drive data block for

specified drive

stack unchanged

note Can be called only from within DOS

18h get something (?)

return DS:SI pointer to (?)

19h unknown

stack word drive (0=default, 1=A:, etc)

return (?)

stack unchanged

note 1) Can be called only from within DOS

2) Calls function 1217h

1Ah get file's drive

DS:SI pointer to filename

return AL drive

(0=default, 1=A:, etc, 0FFh=invalid)

1Bh set something (?)

CL unknown

return AL (?)

note Can be called only from within DOS

1Ch checksum memory

DS:SI pointer to start of memory to checksum

CX number of bytes

DX initial checksum

return DX checksum

note Can be called only from within DOS

1Dh unknown

DS:SI pointer to (?)

CX (?)

DX (?)

return AX (?)

CX (?)

DX (?)

1Eh compare filenames

DS:SI pointer to first ASCIIZ filename

ES:DI pointer to second ASCIIZ filename

return ZF set if filenames equivalent

clear if not

1Fh build drive info block

stack word drive letter

return ES:DI pointer to drive info block

(will be overwritten by next call)

stack unchanged

note Can be called only from within DOS

20h get system file table number

BX file handle

return CF set on error, error code in AL

AL 06h (invalid file handle)

CF clear if successful

byte ES:[DI] = system file table entry

number for file handle

21h unknown

DS:SI pointer to (?)

return (?)

note Can be called only from within DOS

22h unknown

SS:SI pointer to (?)

return nothing(?)

note Can be called only from within DOS

23h check if character device (?)

return DS:SI pointer to device driver with

same name as (?)

note Can be called only from within DOS

24h delay

return after delay of (?) ms

note Can be called only from within DOS

25h get length of ASCIIZ string

DS:SI pointer to ASCIIZ string

return CX length of string

Function 43h Microsoft Extended Memory Specification (XMS)

Function 5453h TesSeRact Standard for Ram-Resident Program Communication

Function 64h SCRNSAV2.COM

entry AH 64h

AL 00h installation check

return AL 00h not installed

0FFh installed

note SCRNSAV2.COM is a screen saver for PS/2's with VGA by Alan Ballard

Function 7Ah Novell NetWare

entry AH 7Ah

AL 00h installation check

note 1) Returns address of entry point for IPX and SPX

2) Parameters are listed under int 21

Function 087h APPEND

entry AH 087h

AL 00h APPEND installation check

return AH <> 0 if installed

01h APPEND - unknown

02h APPEND - version check

Function 088h Microsoft Networks

entry AH 088h

AL 00h network program installation check

return AH <> 0 if installed

BX installed component flags (test in this order!)

bit 6 server

bit 2 messenger

bit 7 receiver

bit 3 redirector

01h unknown

02h unknown

03h get current POST address

return ES:BX POST address

04h set new POST address

ES:BX new POST address

09h network version check

Function 0AAh VIDCLOCK.COM

entry AH 0AAh

AL 00h installation check

return AL 00h not installed

0FFh installed

note VIDCLOCK.COM is a memory-resident clock by Thomas G. Hanlin III

Function 0BBh Network Functions

entry AH 0BBh

AL 00h net command installation check

01h, 02h unknown

03h get server POST address

04h get server POST address

Function 0F7h AUTOPARK.COM (PD TSR hard disk parking utility)

entry AH 0F7h

AL 00h installation check

return AL 00h not installed

0FFh installed

note AUTOPARK is a TSR HD parker by Alan D. Jones

01h set parking delay

BX:CX 32 bit count of 55ms timer ticks

MSDOS 2Fh functions 01h (PRINT), 02h (ASSIGN), 10h (SHARE):

return AX Error

Codes Description

01h invalid function number

02h file not found

03h path not found

04h too many open files

05h access denied

06h invalid handle

08h queue full

09h busy

0Ch name too long

0Fh invalid drive was specified

CF clear (0) if OK

set (1) if error - error returned in AX

note 1) The multiplex numbers AH=0h through AH=7Fh are reserved for DOS.

Applications should use multiplex numbers 80h through 0FFh.

2) When in the chain for int 2Fh, if your code calls DOS or if you execute

with interrupts enabled, your code must be reentrant/recursive.

3) Important! In versions of DOS prior to 3.0, the int 2Fh vector was

initialized to zero rather than being pointed into the DOS service area.

You must initialize this vector manually under DOS 2.x.

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³ Miscellaneous Interrupts - in numerical order ³

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Interrupt 30h (not a vector!) far jump instruction for CP/M-style calls

Interrupt 31h Unknown

note The CALL 5 entry point does a FAR jump to here

Interrupt 32h Unknown

Interrupt 33h Used by Microsoft Mouse Driver

Function Calls

Function Requests

00h Reset Driver and Read Status

entry AH 00h

return AH status

0 hardware/driver not installed

-1 hardware/driver installed

BX number of buttons

-1 two buttons

0 other than two

3 Mouse Systems mouse

01h Show Mouse Cursor

entry AH 01h

return unknown

02h Hide Mouse Cursor

entry AH 02h

return unknown

note multiple calls to hide the cursor will require multiple calls

to function 01h to unhide it.

03h Return Position and Button Status

entry AH 03h

return BX button status

bit 0 left button pressed if 1

bit 1 right button pressed if 1

bit 2 middle button pressed if 1 (Mouse Systems mouse)

CX column

DX row

04h Position Mouse Cursor

entry AH 04h

CX column

DX row

return unknown

05h Return Button Press Data

entry AH 05h

BX button

0 left

1 right

2 middle (Mouse Systems mouse)

return AH button states

bit 0 left button pressed if 1

bit 1 right button pressed if 1

bit 2 middle button pressed if 1 (Mouse Systems mouse)

BX no. of times specified button pressed since last call

CX column at time specified button was last pressed

DX row at time specified button was last pressed

06h Return Button Release Data

entry AH 06h

BX button

0 left

1 right

2 middle (Mouse Systems mouse)

return AH button states

bit 0 left button pressed if 1

bit 1 right button pressed if 1

bit 2 middle button pressed if 1 (Mouse Systems mouse)

BX no. of times specified button released since last call

CX column at time specified button was last released

DX row at time specified button was last released

07h Define Horizontal Cursor Range

entry AH 0007h

CX minimum column

DX maximum column

return unknown

08h Define Vertical Cursor Range

entry AH 08h

CX minimum row

DX maximum row

return unknown

09h Define Graphics Cursor

entry AH 09h

BX column of cursor hot spot in bitmap (-16 to 16)

CX row of cursor hot spot (-16 to 16)

ES:DX pointer to bitmap

16 words screen mask

16 words cursor mask

return unknown

note Each word defines the sixteen pixels of a row, low bit

rightmost

0Ah Define Text Cursor

entry AH 0Ah

BX hardware/software text cursor

00h software

CX screen mask

DX cursor mask

01h hardware

CX start scan line

DX end scan line

return unknown

note When the software cursor is selected, the char/attribute data

at the current screen position is ANDed with the screen mask

and the with the cursor mask

0Bh Read Motion Counters

entry AH 0Bh

return CX number of mickeys mouse moved horiz. since last call

DX number of mickeys mouse moved vertically

note 1) A mickey is the smallest increment the mouse can sense.

Positive values indicate up/right

0Ch Define Interrupt Subroutine Parameters

entry AH 0Ch

CX call mask bit

bit 0 call if mouse moves

bit 1 call if left button pressed

bit 2 call if left button released

bit 3 call if right button pressed

bit 4 call if right button released

bit 5 call if middle button pressed (Mouse Systems)

bit 6 call if middle button released (Mouse Systems)

ES:DX address of FAR routine

return unknown

note when the subroutine is called, it is passed these values:

AH condition mask (same bit assignments as call mask)

BX button state

CX cursor column

DX cursor row

DI horizontal mickey count

SI vertical mickey count

0Dh Light Pen Emulation On

entry AH 0Dh

return unknown

0Eh Light Pen Emulation Off

entry AH 0Eh

return unknown

0Fh Define Mickey/Pixel Ratio

entry AH 0Fh

CX number of mickeys per 8 pixels horizontally

DX number of mickeys per 8 pixels vertically

return unknown

10h Define Screen Region for Updating

entry AH 10h

CX,DX X,Y coordinates of upper left corner

SI,DI X,Y coordinates of lower right corner

return unknown

note Mouse cursor is hidden during updating, and needs to be

explicitly turned on again

11h not documented by Microsoft

12h Set Large Graphics Cursor Block

AH 12h

BH cursor width in words

CH rows in cursor

BL horizontal hot spot (-16 to 16)

CL vertical hot spot (-16 to 16)

ES:DX pointer to bit map of screen and cursor maps

return AH -1 if successful

note PC Mouse. Not documented by Microsoft

13h Define Double-Speed Threshold

entry AH 13h

DX threshold speed in mickeys/second,

0 = default of 64/second

return unknown

note If speed exceeds threshold, the cursor's on-screen motion

is doubled

14h Exchange Interrupt Subroutines

entry AH 14h

return unknown

15h Return Drive Storage Requirements

entry AH 15h

return BX size of buffer needed to store driver state

16h Save Driver State

entry AH 16h

ES:DX pointer to buffer

return unknown

17h Restore Driver State

entry AH 17h

ES:DX pointer to buffer containing saved state

return unknown

18h-1Ch not documented by Microsoft; unknown

1Dh Define Display Page Number

entry AH 1Dh

1Eh Return Display Page Number

entry AH 1Eh

return unknown

42h PCMouse - Get MSmouse Storage Requirements

AH 42h

return AX 0FFFFh successful

BX buffer size in bytes for functions 50h and 52h

00h MSmouse not installed

42h functions 42h, 50h, and 52h not supported

52h PCMouse - Save MSmouse State

entry AH 50h

BX buffer size

ES:DX pointer to buffer

return AX 0FFFFh if successful

52h PCMouse - restore MSmouse state

entry AH 52h

BX buffer size

ES:DX pointer to buffer

return AX 0FFFFh if successful

Int 33: In addition, the following functions are appended to BIOS int 10h and

implemented as the EGA Register Interface Library:

0F0h read one register

0F1h write one register

0F2h read consecutive register range

0F3h write consecutive register range

0F4h read non-consecutive register set

0F5h write non-consecutive register set

0F6h revert to default register values

0F7h define default register values

0FAh get driver status

Interrupt 34h Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0D8h

Interrupt 35h Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0D9h

Interrupt 36h Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0DAh

Interrupt 37h Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0DBh

Interrupt 38h Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0DCh

Interrupt 39h Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0DDh

Interrupt 3Ah Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0DEh

Interrupt 3Bh Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates opcode 0DFh

Interrupt 3Ch Turbo C/Microsoft languages - Floating Point emulation

This int emulates instructions with an ES segment override

Interrupt 3Dh Turbo C/Microsoft languages - Floating Point emulation

This interrupt emulates a standalone FWAIT instruction

Interrupt 3Eh Turbo C/Microsoft languages - Floating Point emulation

Interrupt 3Fh Overlay manager interrupt (Microsoft LINK.EXE)

Default overlay interrupt; may be changed with LINK switch

Interrupt 40h Hard Disk BIOS

Pointer to disk BIOS entry when a hard disk controller is

installed. The BIOS routines use int 30h to revector the

diskette handler (original int 13h) here so int 40 may be used

for hard disk control

Interrupt 41h Hard Disk Parameters (XT,AT,XT2,XT286,PS except ESDI disks)

Pointer to first Hard Disk Parameter Block, normally located

in the controller card's ROM. This table may be copied to RAM

and changed, and this pointer revectored to the new table.

note 1) format of parameter table is:

dw cylinders

db heads

dw starting reduced write current cylinder (XT only, 0 for others)

db maximum ECC burst length

db control byte

bits 0-2 drive option (XT only, 0 for others)

bit 3 set if more than 8 heads

bit 4 always 0

bit 5 set if manufacturer's defect map on max cylinder+1

bit 6 disable ECC retries

bit 7 disable access retries

db standard timeout (XT only, 0 for others)

db formatting timeout (XT only, 0 for others)

db timeout for checking drive (XT only, 0 for others)

dw landing zone (AT, PS/2)

db sectors/track (AT, PS/2)

db 0

2) normally vectored to ROM table when system is initialized.

Interrupt 42h Pointer to screen BIOS entry (EGA, VGA, PS/2)

Relocated (by EGA, etc.) video handler (original int 10h).

Revectors int 10 calls to EGA BIOS.

Interrupt 43h Pointer to EGA graphics character table. The POST initializes

this vector pointing to the default table located in the EGA

ROM BIOS. (PC-2 and up). Not initialized if EGA not present.

This vector was referred to (mistakenly) as the Video

Parameters table in the original EGA BIOS listings.

Interrupt 44h Pointer to graphics character table. This table contains the

(0:0110h) dot patterns for the first 128 characters in video modes 4,5,

and 6, and all 256 characters in all additional graphics modes.

Not initialized if EGA not present.

2) EGA/VGA/CONV/PS - EGA/PCjr fonts, characters 00h to 7Fh

3) Novell NetWare - High-Level Language API

4) This interrupt is not used by some EGA cards.

Interrupt 45h Reserved by IBM (not initialized)

Interrupt 46h Pointer to second hard disk, parameter block (AT, XT/286, PS/2)

(see int 41h) (except ESDI hard disks) (not initialized unless

specific user software calls for it)

Interrupt 47h Reserved by IBM (not initialized)

Interrupt 48h Cordless Keyboard Translation (PCjr, XT [never delivered])

(0:0120h) This vector points to code to translate the cordless keyboard

scancodes into normal 83-key values. The translated scancodes

are then passed to int 9. (not initialized on PC or AT)

Interrupt 49h Non-keyboard Scan Code Translation Table Address (PCjr)

(0:0124h) This interrupt is used for operation of non-keyboard devices

on the PCjr, such as the Keystronic Numeric Keypad.

This interrupt has the address of a table used to translate

non-keyboard scancodes (greater than 85 excepting 255). This

interrupt can be revectored by a user application. IBM

recommends that the default table be stored at the beginning

of an application that required revectoring this interrupt,

and that the default table be restored when the application

terminates. (not initialized on PC or AT)

The PCjr BIOS can interpret scancodes other than those

generated by the keyboard to allow for expansion. The keyboard

generates scancodes from 01h to 055h, including 0FFh. Any

scancodes above 55h (56h through 7Eh for make codes and 0D6h

through 0FEh for break codes) are processed in the following

manner:

1) if the incoming make code falls within the range of the

translate table whose address is pointed to by int 49h, it

is translated into the corresponding scancode. Any incoming

break codes above 0D5h are ignored.

2) if the new translated scancode ius less and 56h, it is

processed by the BIOS as a keyboard scancode and the same

data is placed in the BIOS keyboard buffer.

3) if the translated scancode is higher than 55h or the

incoming scancode is outside the range of the translate

table, 40h is added creating a new extended scancode. The

extended scancode is placed in the BIOS keyboard buffer with

the character code of 00h (NUL). This utilitizes the range

of 96h through 0BEh for scancodes 56h through 7Eh.

The default translate-table maps scancodes 56h through 6Ah to

existing keyboard values. Codes 6Bh theough 0BEh are mapped (by

adding 40h) to extended codes 0ABh through 0FEh since they are

outside the range of the default translate table.

The format of the translate table is:

0 length - the number of nonkeyboard scancodes that are

mapped within the table (from 1 to n)

1 to n word high byte 00h (NUL) byte scancode with low order

byte representing the scancode mapped values relative

to their input values within the range of 56h through

7Eh

With this layout, all keyboard scancodes can be intercepted

through int 9h and and nonkeyboard scancodes can be intercepted

through int 48h.

Interrupt 4Ah Real-Time Clock Alarm (Convertible, PS/2)

(not initialized on PC or AT)

Invoked by BIOS when real-time clock alarm occurs

Interrupt 4Bh Reserved by IBM (not initialized)

Interrupt 4Ch Reserved by IBM (not initialized)

Interrupt 4Dh Reserved by IBM (not initialized)

Interrupt 4Eh Reserved by IBM (not initialized)

Used instead of int 13h for disk I/O on TI Professional PC

Interrupt 4Fh Reserved by IBM (not initialized)

Interrupt 50-57 IRQ0-IRQ7 relocated by DesQview

(normally not initialized)

Interrupt 58h Reserved by IBM (not initialized)

Interrupt 59h Reserved by IBM (not initialized)

GSS Computer Graphics Interface (GSS*CGI)

DS:DX Pointer to block of 5 array pointers

return CF 0

AX return code

CF 1

AX error code

note 1) Int 59 is the means by which GSS*CGI language bindings

communicate with GSS*CGI device drivers and the GSS*CGI

device driver controller.

2) Also used by the IBM Graphic Development Toolkit

Interrupt 5Ah Reserved by IBM (not initialized)

Interrupt 5Bh Reserved by IBM (not initialized)

Interrupt 5Ah Cluster Adapter BIOS entry address

(normally not initialized)

Interrupt 5Bh Reserved by IBM (not initialized) (cluster adapter?)

Interrupt 5Ch NETBIOS interface entry port

ES:BX pointer to network control block

return AL error code (0 if none)

note 1) When the NETBIOS is installed, interrupts 13 and 17 are interrupted by

the NETBIOS; interrupt 18 is moved to int 86 and one of int 2 or 3 is

used by NETBIOS. Also, NETBIOS extends the int 15 function 90 and 91h

functions (scheduler functions)

2) Normally not initialized.

3) TOPS network card uses DMA 1, 3 or none.

Interrupt 5Dh Reserved by IBM (not initialized)

Interrupt 5Eh Reserved by IBM (not initialized)

Interrupt 5Fh Reserved by IBM (not initialized)

Interrupt 60h-67h User Program Interrupts (availible for general use)

Various major programs make standardized use of this group

of interrupts. Details of common use follows

Interrupt 60h 10-Net Network

entry AH 11h Lock and Wait

AL drive number or 0

DX number of seconds to wait

ES:SI Ethernet address or 0

DS:BX pointer to 31-byte ASCIIZ semaphore name

return AL status

0 successful

1 timeout

2 server not responding

3 invalid semaphore name

4 semaphore list is full

5 invalid drive ID

6 invalid Ethernet address

7 not logged in

8 write to network failed

9 semaphore already logged for this CPU

entry AH 12h Lock

AL drive number or 0 for default

ES:SI Ethernet address or 0

DS:BX pointer to 31-byte ASCIIZ semaphore name

return AL status (see function 11h)

1 semaphore currently logged

note Unlike function 11h, this function returns immediately

entry AH 13h Unlock

AL drive number or 0

ES:SI Ethernet address or 0

DS:BX pointer to 31-byte ASCIIZ semaphore name

return AL status (see function 11h)

1 semaphore not logged

Interrupt 67h Used by Lotus-Intel-Microsoft Expanded Memory Specification

user and Ashton-Tate/Quadram/AST Enhanced Expanded Memory

specification (See Chapter 10)

Interrupt 68h Not Used (not initialized)

Interrupt 69h Not Used (not initialized)

Interrupt 6Ah Not Used (not initialized)

Interrupt 6Bh Not Used (not initialized)

Interrupt 6Ch System Resume Vector (Convertible) (not initialized on PC)

DOS 3.2 Realtime Clock update

Interrupt 6Dh Not Used (not initialized)

Interrupt 6Eh Not Used (not initialized)

Interrupt 6Fh Novell NetWare - PCOX API (3270 PC terminal interface)

Interrupt 6Fh 10-Net Network API

entry AH 00h Login

DS:DX login record

8 bytes user name

8 bytes password

12 bytes name of super-station

return CL security level

AX status

0000h good login

0FF01h no response from superstation

0FF02h network error

0FF03h invalid password

0FF04h no local buffer

0FF05h superstation not available

0FF06h node already logged in

0FF07h login not valid from this node

0FF08h node ID already in use

01h Logoff

return CX number of files closed

AX status

0000h successful

0FF08h superstation ID not already logged in

02h Status of node

DS:DX pointer to 512-byte record

8 bytes user name (0 if none)

byte station type

0 workstation

1 superstation

4 logged into multiple superstations

24 bytes list of superstations logged into more than one

superstation

12 bytes node ID

word message count for this station (send for user

node, receive for superstations)

for superstations only:

word drives allocated (bit 0=A:, bit 1=B:,...)

byte user service flag

bit 4: SUBMIT is on

3: mail waiting for node

2: calendar waiting for you

1: news waiting for you

0: mail waiting for you

byte printers allocated (bit 0=LPT1,...)

byte number of unprinted spool files

byte number of opened files

byte number of logged on files

byte primary drive (1=A:)

byte reserved

n bytes list of logged on node IDs (each 12 bytes, max

38 IDs)

return CF set on error

AX error code

0FF01h no response from node

0FF02h network error

0FF04h no local buffer

0FF16h invalid node ID

03h Get Address of Configuration Table

return ES:BX pointer to record (actually starts at [BX-25])

word count of dropped Send6F

word buffer start address

word comm driver base address

word send/receive retry count

byte number of 550ms loops

word UFH address

word CDIR address

word LTAB address

word SFH address

word FTAB address

word RLTAB address

word SMI address

word NTAB address

ES:BX pointer to word address of first CT_DRV

byte number of DRV entries

8 bytes login name

12 bytes node ID

6 bytes node address

byte flag

byte CT_CFLG

bit 1: sound bell

bit 0: CHAT permit

byte CT_PSFLG

bit 5: PRINT permit

bit 4: KB initiated

bit 3: CHAT called FOXPTRM

bit 2: SUBMIT active

bit 1: SUBMIT received

bit 0: SUBMIT permit

byte reserved

word receive message count

word send message count

word retry count

word failed count

word driver errors

word dropped responses/CHATs

9 bytes list ID/NTAB address (3 entries-LPT1-3?)

6 bytes AUX ID/NTAB address (2 entries-COM1-2?)

byte active CB channel

byte received 6F messages on queue

9 bytes activity counters for channels 1-9

04h Send

DS:BX pointer to record

12 bytes receiving node's ID

word length of data at DX

DS:DX pointer to data (max 1024 bytes)

return CF set on error

AX error code

0FF01h timeout

0FF02h network error

0FF04h no local buffer

0FF16h invalid parameter (bad length)

05h Receive

CX number of seconds before timeout

DS:DX pointer to receive buffer

12 bytes sending node's ID

word length of message

n bytes message (maximum 1024 bytes)

return CF set on error

AX error code

0FF01h timeout

0FF18h sent message has been dropped

06h Unknown

07h Lock Handle

BX file handle

CX:DX starting offset in file

SI record length

return CF set on error

AX error code

0FF01h timeout

02h file not found

0FF17h record locked by another user

08h Unlock Handle

BX file handle

AL mode

0 unlock all

1 unlock record at CX:DX

return CF set on error

AX error code

02h file not found

0Bh Lock Semaphore, Return Immediately

AL drive number or 0

ES:SI Ethernet address or 0

DS:BX pointer to 31-byte ASCIIZ semaphore name

return AL status

0 successful

1 semaphore currently locked

2 server not responding

3 invalid semaphore name

4 semaphore list is full

5 invalid drive ID

6 invalid Ethernet address

7 not logged in

8 write to network failed

9 semaphore already logged in this CPU

0Ch unlock semaphore

AL drive number or 0

ES:SI Ethernet address or 0

DS:BX pointer to 31-byte ASCIIZ semaphore name

return AL status (see AH=0Bh)

1 semaphore not locked

0Dh Who

CX length of data

DS:DX pointer to array of records to be filled

12 bytes node ID

byte flag (1=workstation, 2=superstation)

return CL number of records returned (responding stations)

0Eh spool/print

DS:DX pointer to record

word 0 initiate spool

1 abort print

2 close spool

3 delete spool

4 print

5 get report info

11 bytes file name

byte notification

bit 6: do ID page

bit 5: no form feed

bit 3: notify at print completion

bit 2: notify at print start and reply?

bit 1: notify at print start

bit 0: no notification

byte days to keep (0FFh=forever)

byte device (1=LPT1)

word length of following data area

n bytes $SCNT records returned if code in first word

is 05h

return CF set on error

AX error code

0FF16h invalid parameter

0FF17h device not mounted

0FF18h already spooling to named device

11h Lock FCB

AL mode

0 sequential

1 random

2 random block

DS:DX pointer to FCB

return CF set on error

AX 02h file not found

0FF01h timeout

0FF17h record locked by another user

12h Unlock FCB

AL mode

0 sequential

1 random

2 random block

DS:DX pointer to FCB

return CF set on error

AX 02h file not found

Interrupt 70h IRQ 8, Real Time Clock Interrupt (AT, XT/286, PS/2)

Interrupt 71h IRQ 9, Redirected to IRQ 8 (AT, XT/286, PS/2)

LAN Adapter 1 (rerouted to int 0Ah [IRQ2] by BIOS)

Interrupt 72h IRQ 10 (AT, XT/286, PS/2) Reserved

Interrupt 73h IRQ 11 (AT, XT/286, PS/2) Reserved

Interrupt 74h IRQ 12 Mouse Interrupt (PS/2)

Interrupt 75h IRQ 13, Coprocessor Error, BIOS Redirect to int 2 (NMI) (AT)

Interrupt 76h IRQ 14, Hard Disk Controller (AT, XT/286, PS/2)

Interrupt 77h IRQ 15 (AT, XT/286, PS/2) Reserved

Interrupt 78h Not Used

Interrupt 79h Not Used

Interrupt 7Ah Novell NetWare - LOW-LEVEL API

Interrupt 7Bh-7Eh Not Used

Interrupt 7Fh unknown

Used by second copy of COMMAND set with SHELL=

Not used by COMMAND /C at DOS prompt

Interrupt 80h-85h Reserved by BASIC

note interrupts 80h through ECh are apparently unused and not initialized.

Interrupt 86h Relocated by NETBIOS int 18

Interrupt 86h-0F0h Used by BASIC when BASIC interpreter is running

Intrerrupt 0E0h CP/M-86 function calls

Interrupt 0E4h Logitech Modula-2 v2.0 MONITOR

entry AX 05h monitor entry

06h monitor exit

BX priority

Interrupt 0F0h unknown

Used by secondary copy of COMMAND when SHELL= set

Not used by COMMAND /C at DOS prompt

Interrupts 0F1h-0FFh (absolute addresses 3C4-3FF)

Location of Interprocess Communications Area

Interrupt 0F8h Set Shell Interrupt (OEM)

Set OEM handler for int 21h calls from 0F9h through 0FFh

entry AH 0F8h

DS:DX pointer to handler for Functions 0F9h thru 0FFh

note 1) To reset these calls, pass DS and DX with 0FFFFh. DOS is set up to

allow ONE handler for all 7 of these calls. Any call to these handlers

will result in the carry bit being set and AX will contain 1 if they are

not initialized. The handling routine is passed all registers just as

the user set them. The OEM handler routine should be exited through an

IRET.

2) 10 ms interval timer (Tandy?)

Interrupt 0F9h First of 8 SHELL service codes, reserved for OEM shell (WINDOW);

use like HP Vectra user interface?

Interrupt 0FAh USART ready (RS-232C)

Interrupt 0FBh USART RS ready (keyboard)

Interrupt 0FCh Unknown

Interrupt 0FDh reserved for user interrupt

Interrupt 0FEh AT/XT286/PS50+ - destroyed by return from protected mode

Interrupt 0FFh AT/XT286/PS50+ - destroyed by return from protected mode

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

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ISBN 1-878830-02-3 (disk-based text)

C H A P T E R S I X

DOS CONTROL BLOCKS AND WORK AREAS

Contrary to popular belief, DOS is not limited to 640k of work space. This

constraint is enforced by the mapping of ROM and video RAM into the default 1

megabyte CPU address space. Some MSDOS compatible machines, such as the Sanyo

55x series, can have as much as 768k of contiguous DOS workspace with the

appropriate option boards. Since DOS has no real memory management, it cannot

deal with a fragmented workspace. Fragmented RAM (such as RAM mapped into the

option ROM address space) can be dealt with as a RAMdisk or other storage area

by using a device driver or other software.

The 80386 CPU and appropriate control software can create a DOS workspace of

more than one megabyte. Certain add-on boards can also add more than a

megabyte of workspace, but only for specially written software. Since these

are all proprietary schemes, little information is availible at present.

When DOS loads a program, it first sets aside a section of memory for the

program called the program segment, or code segment. Then it constructs a

control block called the program segment prefix, or PSP, in the first 256

(100h) bytes. Usually, the program is loaded directly after the PSP at 100h.

The PSP contains various information used by DOS to help run the program.

The PSP is always located at offset 0 within the code segment. When a program

recieves control certain registers are set to point to the PSP. For a COM

file, all registers are set to point to the beginning of the PSP and the

program begins at 100h. For the more complex EXE file structures, only DS and

ES registers are set to point to the PSP. The linker passes the settings for

the DS, IP, SS, and SP registers and may set the starting location in CS:IP to

a location other than 100h.

IBMBIO provides an IRET instruction at absolute address 847h for use as a

dummy routine for interrupts that are not used by DOS. This lets the interrupts

do nothing until their vectors are rerouted to their appropriate handlers.

A storage block is used by DOS to record the amount and location of allocated

memory within the machine's address space.

A storage block, a Program Segment Prefix, and an environment area are built

by DOS for each program currently resident in the address space. The storage

block is used by DOS to record the address range of memory allocated to a

program. It is used by DOS to find the next availible area to load a program

and to determine if there is enough memory to run that porogram. When a

memory area is in use, it is said to be allocated. Then the program ends, or

releases memory, it is said to be deallocated.

A storage block contains a pointer to the Program Segment Prefix associated

with each program. This control block is constructed by IBMDOS for the purpose

of providing standardized areas for DOS/program communication. Within the

PSP are areas which are used to save interrupt vectors, pass parameters to

the program, record disk directory information, and to buffer disk reads and

writes. This control block is 100h bytes in length and is followed by the

program module loaded by DOS.

The PSP contains a pointer to the environment area for that program. This

area contains a copy of the current DOS SET, PROMPT, COMSPEC, and PATH values

as well as any user-set variables. The program may examine and modify this

information as desired.

Each storage block is 10h bytes long, although only 5 bytes are currently

used by DOS. The first byte contains 4Dh (a capital M) to indicate that it

contains a pointer to the next storage block. A 5Ah (a capital Z) in the

first byte of a storage block indicatres there are no more storage blocks

following this one (it is the end of the chain). The identifier byte is

followed by a 2 byte segment number for the associated PSP for that program.

The next 2 bytes contain the number of segments what are allocated to the

program. If this is not the last storage block, then another storage block

follows the allocated memory area.

When the storage block contains zero for the number of allocated segments,

then no storage is allocated to this block and the next storage block

immediately follows this one. This can happen when memory is allocated and

then deallocated repeatedly.

IBMDOS constructs a storage block and PSP before loading the command

interpreter (default is COMMAND.COM).

If the copy of COMMAND.COM is a secondary copy, it will lack an environment

address at PSP+2Ch.

THE DISK TRANSFER AREA (DTA)ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

DOS uses an area in memory to contain the data for all file reads and writes

that are performed with FCB function calls. This are is known as the disk

transfer area. This disk transfer area (DTA) is sometimes called a buffer.

It can be located anywhere in the data area of your application program and

should be set by your program.

Only one DTA can be in effect at a time, so your program must tell DOS what

memory location to use before using any disk read or write functions. Use

function call 1Ah (Set Disk Transfer Address) to set the disk transfer address.

Use function call 2Fh (Get Disk Transfer Address) to get the disk transfer

address. Once set, DOS continues to use that area for all disk operations until

another function call 1Ah is issued to define a new DTA. When a program is given

control by COMMAND.COM, a default DTA large enough to hold 128 bytes is

established at 80h into the program's Program Segment Prefix.

For file reads and writes that are performed with the extended function calls,

there is no need to set a DTA address. Instead, specify a buffer address when

you issue the read or write call.

DOS PROGRAM SEGMENTÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

When you enter an external command or call a program through the EXEC function

call, DOS determines the lowest availible address space to use as the start of

available memory for the program being started. This area is called the Program

Segment.

At offset 0 within the program segment, DOS builds the Program Segment Prefix

control block. EXEC loads the program after the Program Segment Prefix (at

offset 100h) and gives it control.

The program returns from EXEC by a jump to offset 0 in the Program Segment

Prefix, by issuing an int 20h, or by issuing an int 21h with register AH=00h or

4Ch, or by calling location 50h in the PSP with AH=00h or 4Ch.

It is the responsibility of all programs to ensure that the CS register

contains the segment address of the Program Segment Prefix when terminating by

any of these methods except call 4Ch.

All of these methods result in returning to the program that issued the EXEC.

During this returning process, interrupt vectors 22h, 23h, and 24h (Terminate,

Ctrl-Break, and Critical Error Exit addresses) are restored from the values

saved in the PSP of the terminating program. Control is then given to the

terminate address.

When a program receives control, the following conditions are in effect:

For all programs:

1) The segment address of the passed environment is contained at offset 2Ch in

the Program Segment Prefix.

2) The environment is a series of ASCII strings totalling less than 32k bytes

in the form: NAME=value The default environment is 160 bytes.

Each string is a maximum of 127 bytes terminated by a byte of zeroes for a

total of 128 bytes, and the entire set of strings is terminated by another

byte of zeroes. Following the byte of zeroes that terminates the set of

environment string is a set of initial arguments passed to a program that

contains a word count followed by an ASCIIZ string. The ASCIIZ string

contains the drive, path, and filename.ext of the executable program.

Programs may use this area to determine where the program was loaded from.

The environment built by the command processor (and passed to all programs

it invokes) contains a COMSPEC=string at a minimum (the parameter on COMSPEC

is the path used by DOS to locate COMMAND.COM on disk). The last PATH and

PROMPT commands issued will also be in the environment, along with any

environment strings entered through the SET command.

The environment that you are passed is actually a copy of the invoking

process's environment. If your application terminates and stays resident

through int 27h, you should be aware that the copy of the environment passed

to you is static. That is, it will not change even if subsequent PATH,

PROMPT, or SET commands are issued.

The size of the environment may be changed from its default of 160 bytes

by using the SHELL= command in the config.sys from in DOS version 3.1 up,

or COMMAND.COM may be patched in earlier versions.

The environment can be used to transfer information between processes or to

store strings for later use by application programs. The environment is

always located on a paragraph boundary. This is its format:

byte ASCIIZ string 1

byte ASCIIZ string 2

....

byte ASCIIZ string n

byte of zeros (0)

Typically the environment strings have the form:

NAME = VALUE

The length of NAME or VALUE can be anything desired as long as it still fits

into the 123 byte space (4 bytes are used by "SET ").

Following the byte of zeros in the environment, a WORD indicates the number

of other strings following.

If the environment is part of an EXECed command interpreter, it is followed

by a copy of the DS:DX filename passed to the child process. A zero value

causes the newly created process to inherit the parent's environment.

3) Offset 80h in the PSP contains code to invoke the DOS function dispatcher.

Thus, by placing the desired function number in AH, a program can issue a

long call to PSP+50h to invoke a DOS function rather than issuing an int 21h.

4) The disk transfer address (DTA) is set to 80h (default DTA in PSP).

5) File Control Blocks 5Ch and 6Ch are formatted from the first two parameters

entered when the command was invoked. Note that if either parameter contained

a path name, then the corresponding FCB will contain only a valid drive

number. The filename field will not be valid.

6) An unformatted parameter area at 81h contains all the characters entered

after the command name (including leading and imbedded delimiters), with 80h

set to the number of characters. If the <, >, or | parameters were entered

on the command line, they (and the filenames associated with them) will not

appear in this area, because redirection of standard input and output is

transparent to applications.

(For EXE files only)

7) DS and ES registers are set to point to the PSP.

8) CS, IP, SS, and SP registers are set to the values passed by the linker.

(For COM files only)

9) For COM files, offset 6 (one word) contains the number of bytes availible in

the segment.

10) Register AX reflects the validity of drive specifiers entered with the

first two parameters as follows:

AL=0FFh is the first parameter contained an invalid drive specifier,

otherwise AL=00h.

AL=0FFh if the second parameter contained an invalid drive specifier,

otherwise AL=00h.

11) All four segment registers contain the segment address of the inital

allocation block, that starts within the PSP control block. All of user

memory is allocated to the program. If the program needs to invoke another

program through the EXEC function call (4Bh), it must first free some memory

through the SETBLOCK function call to provide space for the program being

invoked.

12) The Instruction Pointer (IP) is set to 100h.

13) The SP register is set to the end of the program's segment. The segment size

at offset 6 is rounded down to the paragraph size.

14) A word of zeroes is placed on top of the stack.

The PSP (with offsets in hexadecimal) is formatted as follows:

(* = undocumented)

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ P R O G R A M S E G M E N T P R E F I X ³

ÃÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ offset³ size ³ C O N T E N T S ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0000h ³ 2 bytes ³ int 20h ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0002h ³ 2 bytes ³ segment address, end of allocation block ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0004h ³ 1 byte ³ reserved, normally 0 ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0005h ³ 5 bytes ³ FAR call to MSDOS function dispatcher (int 21h) ³

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³ 000Ah ³ 4 bytes ³ previous termination handler interrupt vector (int 22h) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 000Eh ³ 4 bytes ³ previous contents of ctrl-C interrupt vector (int 23h) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0012h ³ 4 bytes ³ prev. critical error handler interrupt vector (int 24h) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0016h ³ 22 bytes ³ reserved for DOS ³

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

* ³ 2 bytes ³ (16) parent process' PSP ³

* ³ 20 bytes ³ (18) "handle table" used for redirection of files ³

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³ 002Ch ³ 2 bytes ³ segment address of the program's environment block ³

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³ 002Eh ³ 34 bytes ³ reserved, DOS work area ³

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

* ³ 4 bytes ³ (2E) stores the calling process's stack pointer when ³

³ ³ switching to DOS's internal stack. ³

* ³ ³ (32) DOS 3.x max open files ³

* ³ 2 bytes ³ (3A) size of handle table |these functions are in here ³

* ³ 4 bytes ³ (3C) handle table address |but reported addresses vary ³

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0050h ³ 3 bytes ³ int 21h, RETF instruction ³

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³ 0053h ³ 2 bytes ³ reserved - unused? ³

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³ 0055h ³ 7 bytes ³ reserved, or FCB#1 extension ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 005Ch ³ 16 bytes ³ default unopened File Control Block #1 ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 006Ch ³ 16 bytes ³ default unopened FCB #2 (overlaid if FCB #1 opened) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0080h ³ 1 byte ³ parameter length (number of chars entered after filename) ³

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³ 0081h ³ ... ³ parameters ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 00FFh ³ 128 bytes³ command tail and default Disk Transfer Area (DTA) ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

1. The first segment of availible memory is in segment (paragraph) form. For

example, 1000h would respresent 64k.

2. Offset 2Ch contains the segment address of the environment.

3. Programs must not alter any part of the PSP below offset 5Ch.

PSP (comments):

offset 00h contains hex bytes CD 20, the int 20h opcode. A program can end

by making a jump to this location when the CS points to the PSP.

For normal cases, int 21, function 4Ch should be used.

offset 02h contains the segment-paragraph address of the end of memory as

reported by DOS. (which may not be the same as the real end of RAM).

Multiply this number by 10h or 16 to get the amount of memory

availible. ex. 1000h would be 64k.

offset 04h "reserved or used by DOS" according to Microsoft

offset 05h contains a long call to the DOS function dispatcher. Programs may

jump to this address instead of calling int 21 if they wish.

Used by Basic and other CPM object-code translated programs. It is

slower than standard int 21h.

offset 0Ah, 0Eh, 12h

vectors (IP, CS)

offset 16h PSP:16h is the segment address of the invoking program's PSP, which

* will most often be COMMAND.COM but perhaps may be a secondary

non-permanent COMMAND or a multitasking shell, etc. At any rate,

the resident shell version of COMMAND.COM has PSP:16H = PSP, which

indicates "don't look any lower in memory" for the command

interpreter. To find the beginning of the allocation chain, look

backwards through the PSP link addresses until the link address is

equal to the PSP segment address that it resides in. This should

be COMMAND.COM. To find COMMAND.COM's environment, look at the word

stored at offset 0BD3h (PC-DOS 3.1 only). This is a segment

address, so look there at offset 0.

18h handle alias table (networking). Also you can make PRN go to CON,

* CON go to PRN, ERR go to PRN, etc. 0FFh = availible.

offset 2Ch is the segment:offset address of the environment for the program

using this particular PSP. This pointer does not point to

COMMAND.COM's environment unless it is a second copy of COMMAND.

offset 2Eh the DWORD at PSP+2Eh is used by DOS to store the calling process's

* stack pointer when switching to DOS's own private stack - at the end

of a DOS function call, SS:SP is restored from this address.

32h, 34h

* table of number of file handles (to 64k of handles!)

offset 40h 2 byte field points to the segment address of COMMAND.COM's PSP in

* "weird" EXE files produced by Digital Research RASMPC/LINKPC.

EXE files created with these tools can cause all sorts of problems

with standard MSDOS debugging tools.

offset 50h contains a long call to the DOS int 21 function dispatcher.

offset 5Ch, 65h, 6Ch

contain FCB information for use with FCB function calls. The first

FCB may overlay the second if it is an extended call; your program

should revector these areas to a safe place if you intend to use

them.

offset 5Ch 16 bytes first command-line argument (formatted as uppercase 11

character filename)

offset 6Ch 16 bytes second command-line argument (formatted as uppercase 11

character filename)

offset 7Ch-7Fh

"reserved or used by DOS"

offset 80h 1 byte number of bytes in command line argument

offset 80h, 81h

contain the length and value of parameters passed on the command

line.

offset 81h 97 bytes unformatted command line and/or default DTA

offset 0FFh contains the DTA

The PSP is created by DOS for all programs and contains most of the information

you need to know about a program running. You can change the environment for

the current process, however, but for the parent process, DOS in this case, you

need to literally backtrack to DOS or COMMAND.COM's PSP. In order to get there

you must look at the current PSP. At offset 16h of the current PSP segment,

there a 2 byte segment address to the parent or previous process PSP.

From there you can manipulate the enviroment by looking at offset 2Ch. As you

know, at offset 2Ch, there is 2 byte segment address to the environment block.

Try this under debug and explore the addresses located at these offsets;

offset length description

------------------------------------------------------------

16h 2 segment address of parent process PSP

2Ch 2 segment address of environment block.

Remember under debug you will have to backtrack two times.

Programs Parent

--------------------------

command.com none

debug.com command.com

program debug.com

MEMORY CONTROL BLOCKSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

DOS keeps track of allocated and availible memory blocks, and provides four

function calls for application programs to communicate their memory needs to

DOS. These calls are:

48h --- allocate memory (MALLOC)

49h --- free allocated memory

4Ah --- modify allocated memory blocks (SETBLOCK)

4Bh --- load or execute program (EXEC)

DOS manages memory as follows:

DOS build a control block for each block of memory, whether free or allocated.

For example, if a program issues an "allocate" (48h), DOS locates a block of

free memory that satisfies the request, and then "carves" the requested memory

out of that block. The requesting program is passed the location of the first

byte of the block that was allocated for it - a memory management control block,

describing the allocated block, has been built for the allocated block and a

second memory management control block describes the amount of space left in the

original free block of memory. When you do a SETBLOCK to shrink an allocated

block, DOS builds a memory management control block for the area being freed and

adds it to the chain of control blocks. Thus, any program that changed memory

that is not allocated to it stands a chance of destroying a DOS memory

management control block. This causes unpredictable results that don't show up

until an activity is performed where DOS uses its chain of control blocks. The

normal result is a memory allocation error, which means a system reset will be

required.

When a program (command or application program) is to be loaded, DOS uses the

EXEC function call 4Bh to perform the loading.

This is the same function call that is availible to applications programs for

loading other programs. This function call has two options:

Function 00h, to load and execute a program (this is what the command

processor uses to load and execute external commands)

Function 03h, to load an overlay (program) without executing it.

Although both functions perform their loading in the same way (relocation is

performed for EXE files) their handling of memory management is different.

FUNCTION 0: For function 0 to load and execute a program, EXEC first allocates

the largest availible block of memory (the new program's PSP will be at offset

0 in that block). Then EXEC loads the program. Thus, in most cases, the new

program owns all the memory from its PSP to the end of memory, including memory

occupied by the transient parent of COMMAND.COM. If the program were to issue

its own EXEC function call to load and execute another program, the request

would fail because no availible memory exists to load the new program into.

NOTE: For EXE programs, the amount of memory allocated is the size of the

program's memory image plus the value in the MAX_ALLOC field of the file's

header (offset 0Ch, if that much memory is availible. If not, EXEC

allocates the size of the program's memory image plus the value in the

MIN_ALLOC field in the header (offset 0Ah). These fields are set by the

Linker).

A well-behaved program uses the SETBLOCK function call when it receives

control, to shrink its allocated memory block down to the size it really needs.

A COM program should remember to set up its own stack before doing the SETBLOCK,

since it is likely that the default stack supplied by DOS lies in the area of

memory being used. This frees unneeded memory, which can be used for loading

other programs.

If the program requires additional memory during processing, it can obtain

the memory using the allocate function call and later free it using the free

memory function call.

When a program is loaded using EXEC function call 00h exits, its initial

allocation block (the block beginning with its PSP) is automatically freed

before the calling program regains control. It is the responsibility of all

programs to free any memory they allocate before exiting to the calling

program.

FUNCTION 3: For function 3, to load an overlay, no PSP is built and EXEC

assumes the calling program has already allocated memory to load the new program

into - it will NOT allocate memory for it. Thus the calling program should

either allow for the loading of overlays when it determines the amount of memory

to keep when issuing the SETBLOCK call, or should initially free as much memory

as possible. The calling program should then allocate a block (based on the size

of the program to be loaded) to hold the program that will be loaded using the

"load overlay" call. Note that "load overlay" does not check to see if the

calling program actually owns the memory block it has been instructed to load

into - it assumes the calling program has followed the rules. If the calling

program does not own the memory into which the overlay is being loaded, there is

a chance the program being loaded will overlay one of the control blocks that

DOS uses to keep track of memory blocks.

Programs loaded using function 3 should not issue any SETBLOCK calls since

they don't own the memory they are operating in. (This memory is owned by the

calling program)

Because programs loaded using function 3 are given control directly by (and

return contrrol directly to) the calling program, no memory is automatically

freed when the called program exits. It is up to the calling program to

determine the disposition of the memory that had been occupied by the exiting

program. Note that if the exiting program had itself allocated any memory, it

is responsible for freeing that memory before exiting.

Memory control blocks, sometimes called "arena headers" after their UNIX

counterpart, are 16 bytes long. Only the first 5 bytes are used. 16 bytes are

used for the memory control block, which always starts at a paragraph boundary.

When DOS call 48h is made to allocate "x" many paragraphs of memory, the amount

used up is actually one more than the figure in the BX register to provide

space for the associated memory control block. The location of the memory

control block is at the paragraph immediately before the segment value returned

in AX by the DOS function 48h call i.e. ((AX-1):0).

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ M E M O R Y C O N T R O L B L O C K ³

ÃÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ Bytes ³ Function ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0 ³ ASCII M or Z ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1-2 ³ PSP segment address of the program that owns this block of memory ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 3-4 ³ Size of next MCB in 16-byte paragraphs ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 5-F ³ unused ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

byte 1 will always have the value of 4Dh or 5Ah. The value 5Ah (Z) indicates

the block is the last in a chain, all memory above it is unused. 4Dh

(M) means that the block is intermediate in a chain, the memory above

it belongs to the next program or to DOS.

byte 2,3 hold the PSP segment address of the program that owns the

corresponding block of memory. A value of 0 means the block is free

to be claimed, any other value represents a segment address.

byte 3, 4 indicate the size in paragraphs of the memory block. If you know the

address of the first block, you can find the next block by adding the

length of the memory block plus 1 to the segment address of the

control block. Finding the first block can be difficult, as this

varies according to the DOS version and the configuration.

The remaining 11 bytes are not currently used by DOS, and may contain "trash"

characters left in memory from previous applications.

If DOS determines that the allocation chain of memory control blocks has been

corrupted, it will halt the system and display the message "Memory Allocation

Error", and the system will halt, requiring a reboot.

Each memory block consists of a signature byte (4Dh or 5Ah) then a word which

is the PSP value of the owner of the block (which allocated it), followed by a

word which is the size in paragraphs of the block. The last block has a

signature of 5Ah. All others have 4Dh. If the owner is 0000 then the block is

free.

Once a memory control block has been created it should only be manipulated

with the appropriate DOS function calls. Accidentally writing over any of the

first 5 bytes of a memory control block can cause a memory allocation error

and cause the system to lock up. If the first byte is overwritten with

something other than an 'M' or a 'Z' then DOS will complain with an error

return code of 7 signifying "Memory Control Blocks destroyed". However, should

you change the ownership or block size bytes, you've had it.

When a .COM program is first loaded by DOS and given control, the memory

control block immediately preceding the Program Segment Prefix contains the

following data:

ID = 'Z'

Owner = segment address of PSP (= CS register of .COM program)

Size = number of available paragraphs in DOS memory pool

An .EXE file will have the following data in the memory control block for

the program (just prior to the PSP):

ID = 'M'

Owner = segment address of PSP (= DS register of program)

Size = the number of paragraphs allocated to the program according

to the information in the .EXE program header

In the case of an .EXE program file the amount of memory allocated depends

on the contents of the program header which informs the DOS loader how much to

allocate for each of the segments in the program. With an .EXE program file

there will always be a 'Z' memory control block created in memory immediately

after the end of the space allocated to the program itself.

One important fact to remember about DOS memory allocation is that blocks of

RAM allocated by different calls to DOS function 48H will NOT be contiguous. At

the very best, they will be separated by the 16 bytes of the memory control

block, and at worst they could be anywhere in RAM that DOS manages to find a

existing memory control block of sufficient size to accomodate the memory

request.

DOS treats the memory control blocks as a kind of linked list (term used

loosely). It uses the earlier MCBs to find the later ones by calculating the

location of the next one from the size of the prior one. As such, erasing any

of the MCB data in the chain of MCBs will upset DOS severely, as each call for

a new memory allocation causes DOS to scan the whole chain of MCBs looking for

a free one that is large enough to fulfill the request.

A separate MCB is created for the DOS environment strings at each program

load, so there will be many copies of the environment strewn through memory

when you have a lot of memory resident programs loaded. The memory control

blocks for the DOS environment strings are not returned to the DOS memory pool

if the program goes resident, as DOS will need to copy this enviroment for the

next program loaded.

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/16/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

C H A P T E R S E V E N

DOS FILE STRUCTURE

FILE MANAGEMENT FUNCTIONSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Use DOS function calls to create, open, close, read, write, rename, find, and

erase files. There are two sets of function calls that DOS provides for support

of file management. They are:

* File Control Block function calls (0Fh-24h)

* Handle function calls (39h-69h)

Handle function calls are easier to use and are more powerful than FCB calls.

Microsoft recommends that the handle function calls be used when writing new

programs. DOS 3.0 up have been curtailing use of FCB function calls; it is

possible that future versions of DOS may not support FCB function calls.

The following table compares the use of FCB calls to Handle function calls:

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ FCB Calls ³ Handle Calls ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ Access files in current ³ Access files in ANY directory ³

³ directory only. ³ ³

³ ³ ³

³ Requires the application ³ Does not require use of an FCB. ³

³ program to maintain a file ³ Requires a string with the drive, ³

³ control block to open, ³ path, and filename to open, create, ³

³ create, rename or delete ³ rename, or delete a file. For file ³

³ a file. For I/O requests, ³ I/O requests, the application program ³

³ the application program ³ must maintain a 16 bit file handle ³

³ also needs an FCB ³ that is supplied by DOS. ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

The only reason an application should use FCB function calls is to maintain

the ability to run under DOS 1.x. To to this, the program may use only function

calls 00h-2Eh. Though the FCB function calls are frowned upon, many of the

introductory assembly language programming texts use the FCB calls as examples.

FCB FUNCTION CALLS ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

FCB function calls require the use of one File Control Block per open file,

which is maintained by the application program and DOS. The application program

supplies a pointer to the FCB and fills in ther appropriate fields required by

the specific function call. An FCB function call can perform file management on

any valid drive, but only in the current logged directory. By using the current

block, current record, and record length fields of the FCB, you can perform

sequential I/O by using the sequential read or write function calls. Random I/O

can be performed by filling in the random record and record length fields.

Several possible uses of FCB type calls are considered programming errors and

should not be done under any circumstances to avoid problems with file sharing

and compatibility with later versions of DOS.

Some errors are:

1) If program uses the same FCB structure to access more than one open file. By

opening a file using an FCB, doing I/O, and then replacing the filename field

in the file control block with a new filename, a program can open a second

file using the same FCB. This is invalid because DOS writes control info-

rmation about the file into the reserved fields of the FCB. If the program

then replaces the filename field with the original filename and then tries to

perform I/O on this file, DOS may become confused because the control info-

rmation has been changed. An FCB should never be used to open a second file

without closing the one that is currently open. If more than one File Control

Block is to be open concurrently, separate FCBs should be used.

2) A program should never try to use the reserved fields in the FCB, as the

function of the fields changes with different versions of DOS.

3) A delete or a rename on a file that is currently open is considered an error

and should not be attempted by an application program.

It is also good programming practice to close all files when I/O is done. This

avoids potential file sharing problems that require a limit on the number of

files concurrently open using FCB function calls.

HANDLE FUNCTION CALLSÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The recommended method of file management is by using the extended "handle"

set of function calls. These calls are not restricted to the current directory.

Also, the handle calls allow the application program to define the type of

access that other processes can have concurrently with the same file if the file

is being shared.

To create or open a file, the application supplies a pointer to an ASCIIZ

string giving the name and location of the file. The ASCIIZ string contains an

optional drive letter, optional path, mandatory file specification, and a

terminal byte of 00h. The following is an example of an ASCIIZ string:

format [drive][path] filename.ext,0

DB "A:\path\filename.ext",0

If the file is being created, the application program also supplies the

attribute of the file. This is a set of values that defines the file read

only, hidden, system, directory, or volume label.

If the file is being opened, the program can define the sharing and access

modes that the file is opened in. The access mode informs DOS what operations

your program will perform on this file (read-only, write-only, or read/write)

The sharing mode controls the type of operations other processes may perform

concurrently on the file. A program can also control if a child process inherits

the open files of the parent. The sharing mode has meaning only if file sharing

is loaded when the file is opened.

To rename or delete a file, the appplication program simply needs to provide

a pointer to the ASCIIZ string containing the name and location of the file

and another string with the new name if the file is being renamed.

The open or create function calls return a 16-bit value referred to as the

file handle. To do any I/O to a file, the program uses the handle to reference

the file. Once a file is opened, a program no longer needs to maintain the

ASCIIZ string pointing to the file, nor is there any need to stay in the same

directory. DOS keeps track of the location of the file regardless of what

directory is current.

Sequential I/O can be performed using the handle read (3Fh) or write (40h)

function calls. The offset in the file that IO is performed to is automatically

moved to the end of what was just read or written. If random I/O is desired, the

LSEEK (42h) function call can be used to set the offset into the file where I/O

is to be performed.

SPECIAL FILE HANDLESÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

DOS reserves five special file handles for use by itself and applications

programs. They are:

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ 0000h ³ STDIN ³ standard input device (input can be redirected) ³

³ 0001h ³ STDOUT ³ standard output device (output can be redirected) ³

³ 0002h ³ STDERR ³ standard error output device (output cannot be redirected) ³

³ 0004h ³ STDAUX ³ standard auxiliary device ³

³ 0005h ³ STDPRN ³ standard printer device ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

These handles are predefined by DOS and can be used by an application program.

They do not need to be opened by a program, although a program can close these

handles. STDIN should be treated as a read-only file, and STDOUT and STDERR

should be treated as write-only files. STDIN and STDOUT can be redirected. All

handles inherited by a process can be redirected, but not at the command line.

These handles are very useful for doing I/O to and from the console device.

For example, you could read input from the keyboard using the read (3Fh)

function call and file handle 0000h (STDIN), and write output to the console

screen with the write function call (40h) and file handle 0001h (STDOUT). If

you wanted an output that could not be redirected, you could output it using

file handle 0002h (STDERR). This is very useful for error messages that must

be seen by a user.

File handles 0003h (STDAUX) and 0004h (STDPRN) can be both read from and

written to. STDAUX is typically a serial device and STDPRN is usually a parallel

device.

ASCII and BINARY MODEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

I/O to files is done in binary mode. This means that the data is read or

written without modification. However, DOS can also read or write to devices in

ASCII mode. In ASCII mode, DOS does some string processing and modification to

the characters read and written. The predefined handles are in ASCII mode when

initialized by DOS. All other file handles that don't refer to devices are in

binary mode. A program, can use the IOCTL (44h) function call to set the mode

that I/O is to a device. The predefined file handles are all devices, so the

mode can be changed from ASCII to binary via IOCTL. Regular file handles that

are not devices are always in binary mode and cannot be changed to ASCII mode.

The ASCII/BINARY bit was called "raw" in DOS 2.x, but it is called ASCII/BINARY

in DOS 3.x.

The predefined file handles STDIN (0000h) and STDOUT (0001h) and STDERR

(0002h) are all duplicate handles. If the IOCTL function call is used to change

the mode of any of these three handles, the mode of all three handles is

changed. For example, if IOCTL was used to change STDOUT to binary mode, then

STDIN and STDERR would also be changed to binary mode.

FILE I/O IN BINARY (RAW) MODEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The following is true when a file is read in binary mode:

1) The characters ^S (scroll lock), ^P (print screen), ^C (control break) are

not checked for during the read. Therefore, no printer echo occurs if ^S or

^P are read.

2) There is no echo to STDOUT (0001h).

3) Read the number of specified bytes and returns immediately when the last

byte is received or the end of file reached.

4) Allows no editing of the ine input using the function keys if the input is

from STDIN (0000h).

The following is true when a file is written to in binary mode:

1) The characters ^S (scroll lock), ^P (print screen), ^C (control break) are

not checked for during the write. Therefore, no printer echo occurs.

2) There is no echo to STDOUT (0001h).

3) The exact number of bytes specified are written.

4) Does not caret (^) control characters. For example, ctrl-D is sent out as

byte 04h instead of the two bytes ^ and D.

5) Does not expand tabs into spaces.

FILE I/O IN ASCII (COOKED) MODEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The following is true when a file is read in ASCII mode:

1) Checks for the characters ^C,^S, and ^P.

2) Returns as many characters as there are in the device input buffer, or the

number of characters requested, whichever is less. If the number of

characters requested was less than the number of characters in the device

buffer, then the next read will address the remaining characters in the

buffer.

3) If there are no more bytes remaining in the device input buffer, read a

line (terminated by ^M) into the buffer. This line may be edited with the

function keys. The characters returned terminated with a sequence of 0Dh,

0Ah (^M,^J) if the number of characters requested is sufficient to include

them. For example, if 5 characters were requested, and only 3 were entered

before the carriage return (0Dh or ^M) was presented to DOS from the console

device, then the 3 characters entered and 0Dh and 0Ah would be returned.

However, if 5 characters were requested and 7 were entered before the

carriage return, only the first 5 characters would be returned. No 0Dh,0Ah

sequence would be returned in this case. If less than the number of

characters requested are entered when the carriage return is received, the

characters received and 0Dh,0Ah would be returned. The reason the 0Ah

(linefeed or ^J) is added to the returned characters is to make the devices

look like text files.

4) If a 1Ah (^Z) is found, the input is terminated at that point. No 0Dh,0Ah

(CR,LF) sequence is added to the string.

5) Echoing is performed.

6) Tabs are expanded.

The following is true when a file is written to in ASCII mode:

1) The characters ^S,^P,and ^C are checked for during the write operation.

2) Expands tabs to 8-character boundaries and fills with spaces (20h).

3) Carets control characters, for example, ^D is written as two bytes, ^ and D.

4) Bytes are output until the number specified is output or a ^Z is

encountered. The number actually output is returned to the user.

NUMBER OF OPEN FILES ALLOWEDÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The number of files that can be open concurrently is restricted by DOS. This

number is determined by how the file is opened or created (FCB or handle

function call) and the number specified by the FCBS and FILES commands in the

CONFIG.SYS file. The number of files allowed open by FCB function calls and the

number of files that can be opened by handle type calls are independent of one

another.

RESTRICTIONS ON FCB USAGEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

If file sharing is not loaded using the SHARE command, there are no

restrictions on the nuumber of files concurrently open using FCB function calls.

However, when file sharing is loaded, the maximum number of FCBs open is set

by the the FCBS command in the CONFIG.SYS file.

The FCBS command has two values you can specify, 'm' and 'n'. The value for

'm' specifies the number of files that can be opened by FCBs, and the value 'n'

specifies the number of FCBs that are protected from being closed.

When the maximum number of FCB opens is exceeded, DOS automatically closes the

least recently used file. Any attempt to access this file results in an int 24h

critical error message "FCB not availible". If this occurs while an application

program is running, the value specified for 'm' in the FCBS command should be

increased.

When DOS determines the least recently used file to close, it does not include

the first 'n' files opened, therefore the first 'n' files are protected from

being closed.

RESTRICTIONS ON HANDLE USAGEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The number of files that can be open simultaneously by all processes is

determined by the FILES command in the CONFIG.SYS file. The number of files a

single process can open depends on the value specified for the FILES command. If

FILES is greater than or equal to 20, a single process can open 20 files. If

FILES is less than 20, the process can open less than 20 files. This value

includes three predefined handles: STDIN, STDOUT, and STDERR. This means only

17 additional handles can be added. DOS 3.3 includes a function to use more than

20 files per application.

ALLOCATING SPACE TO A FILEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Files are not nescessarily written sequentially on a disk. Space is allocated

as needed and the next location availible on the disk is allocated as space for

the next file being written. Therefore, if considerable file generation has

taken place, newly created files will not be written in sequential sectors.

However, due to the mapping (chaining) of file space via the File Allocation

Table (FAT) and the function calls availible, any file may be used in either a

sequential or random manner.

Space is allocated in increments called clusters. Cluster size varies

according to the media type. An application program should not concern itself

with the way that DOS allocates space to a file. The size of a cluster is only

important in that it determines the smallest amount of space that can be

allocated to a file. A disk is considered full when all clusters have been

allocated to files.

MSDOS / PCDOS DIFFERENCESÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

There is a problem of compatibility between MS-DOS and IBM PC-DOS having to

do with FCB Open and Create. The IBM 1.0, 1.1, and 2.0 documentation of OPEN

(call 0Fh) contains the following statement:

"The current block field (FCB bytes C-D) is set to zero [when an FCB is

opened]."

This statement is NOT true of MS-DOS 1.25 or MS-DOS 2.00. The difference is

intentional, and the reason is CP/M 1.4 compatibility. Zeroing that field is

not CP/M compatible. Some CP/M programs will not run when machine translated if

that field is zeroed. The reason it is zeroed in the IBM versions is that IBM

specifically requested that it be zeroed. This is the reason for the complaints

from some vendors about the fact that IBM MultiPlan will not run under MS-DOS.

It is probably the reason that some other IBM programs don't run under MS-DOS.

NOTE: Do what all MS/PC-DOS systems programs do: Set every single FCB field you

want to use regardless of what the documentation says is initialized.

.COM FILE STRUCTUREÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The COM file structure was designed for DOS 1.0 and maximum compatibility

with programs ported from the CP/M operating system. COM files normally

comprise one segment only.

.EXE FILE STRUCTUREÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The EXE file is the native mode for DOS. EXE files may make use of multiple

segments for code, stack, and data. The design of the EXE file reflects the

segmented design of the Intel 80x86 CPU architecture. EXE files may be as

large as availible memory and may make references to specific segment addresses.

The EXE files produced by the Linker program consist of two parts, control and

relocation information and the load module itself.

The control and relocation information, which is described below, is at the

beginning of the file in an area known as the header. The load module

immediately follows the header. The load module begins in the memory image of

the module contructed by the Linker.

When you are loading a file with the name *.EXE, DOS does NOT assume that it

is an EXE format file. It looks at the first two bytes for a signature telling

it that it is an EXE file. If it has the proper signature, then the load

proceeds. Otherwise, it presumes the file to be a .COM format file.

If the file has the EXE signature, then the internal consistency is checked.

Pre-2.0 versions of MSDOS did not check the signature byte for EXE files.

The .EXE format can support programs larger than 64K. It does this by

allowing separate segments to be defined for code, data, and the stack, each

of which can be up to 64K long. Programs in EXE format may contain explicit

references to segment addresses. A header in the EXE file has information for

DOS to resolve these references.

The .EXE header is formatted as follows:

ÚÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Offset ³ C O N T E N T S ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 00h ³ 4Dh ³ This is the Linker's signature to mark the file as a valid ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄ´ .EXE file (The ASCII letters M and Z, for Mark Zbikowski, ³

³ 01h ³ 5Ah ³ one of the major designers of DOS at Microsoft) ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 02h-03h ³ Length of the image mod 512 (remainder after dividing the load ³

³ ³ module image size by 512) ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 04h-05h ³ Size of the file in 512 byte pages including the header. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 06h-07h ³ Number of relocation table items following the header. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 08h-09h ³ Size of the header in 16 byte increments (paragraphs). This is ³

³ ³ used to locate the beginning of the load module in the file. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0Ah-0Bh ³ Minimum number of 16 byte paragraphs required above the end of ³

³ ³ the loaded program. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0Ch-0Dh ³ Maximum number of 16 byte paragraphs required above the end of ³

³ ³ the loaded program. If the minimum and maximum number of ³

³ ³ paragraphs are both zero, the program will be loaded as high in ³

³ ³ memory as possible. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0Eh-0Fh ³ Displacement in paragraphs of stack segment within load module. ³

³ ³ This size must be adjusted by relocation. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 10h-11h ³ Offset to be in SP register when the module is given control. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 12h-13h ³ Word Checksum - negative sum of all the words in the file, ³

³ ³ ignoring overflow. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 14h-15h ³ Offset to be in the IP register when the module is given control. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 16h-17h ³ Displacement in paragraphs of code segment within load module. ³

³ ³ This size must be adjusted by relocation. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 18h-19h ³ Displacement in bytes of the first relocation item in the file. ³

ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1Ah-1Bh ³ Overlay number (0 for the resident part of the program) ³

ÀÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

THE RELOCATION TABLEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The word at 18h locates the first entry in the relocation table. The

relocation table is made up of a variable number of relocation items. The number

of items is contained at offset 06-07. The relocation item contains two fields

- a 2 byte offset value, followed by a 2 byte segment value. These two fields

represent the displacement into the load module before the module is given

control. The process is called relocation and is accomplished as follows:

1. The formatted part of the header is read into memory. Its size is 1Bh.

2. A portion of memory is allocated depending on the size of the load module

and the allocation numbers in offsets 0Ah-0Ch and 0Ch-0Dh. DOS always

tries to allocate 0FFFFh paragraphs. Since this call will always fail,

the function returns the amount of free memory. If this block is larger

than the minimum specified at offset 0Ah and the loaded program size,

DOS will allocate the size specified at offset 0Ch or the largest free

memory space, whichever is less.

3. A Program Segment Prefix is built following the resident portion of the

program that is performing the load operation.

4. The formatted part of the header is read into memory (its size is at

offset 08h)

5. The load module size is determined by subtracting the header size from the

file size. Offsets 04h and 08h can be used for this calculation. The

actual size is downward adjusted based on the contents of offsets 02-03.

Note that all files created by the Linker programs prior to version 1.10

always placed a value of 4 at this location, regardless of the actual

program size. Therefore, Microsoft recommends that this field be ignored if

it contains a value of 4. Based on the setting of the high/low loader switch,

an appropriate segment is determined for loading the load module. This

segment is called the start segment.

6. The load module is read into memory beginning at the start segment. The

relocation table is an ordered list of relocation items. The first relocation

item is the one that has the lowest offset in the file.

7. The relocation table items are read into a work area one or more at a time.

8. Each relocation table item segment value is added to the start segment value.

The calculated segment, in conjunction with the relocation item offset value,

points to a word in the load module to which is added the start segment

value. The result is placed back into the word in the load module.

9. Once all the relocation items have been processed, the SS and SP registers

are set from the values in the header and the start segment value is added

to SS. The ES and DS registers are set to the segment address of the program

segment prefix. The start segment value is added to the header CS register

value. The result, along with the header IP value, is used to give the

module control.

"NEW" .EXE FORMAT (Microsoft Windows and OS/2)ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The "old" EXE format is documented here. The "new" EXE format puts more

information into the header section and is currently used in applications that

run under Microsoft Windows. The linker that creates these files comes with the

Microsoft Windows Software Development Kit and is called LINK4. If you try to

run a Windows-linked program under DOS, you will get the error message "This

program requires Microsoft Windows".

PIF Files

PIF stands for "Program Information File". The PIF format was developed by

IBM for use with TopView, its multitasking manager. Microsoft also uses PIF

files to pass information regarding the amount of memory and type of I/O a

program running under Microsoft Windows requires.

The actual internal format of the PIF files is documented in the IBM TopView

Programmers' ToolKit.

STANDRD FILE CONTROL BLOCKÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The standard file control block is defined as follows, with offsets in hex:

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ F I L E C O N T R O L B L O C K ³

ÃÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ Bytes ³ Function ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0 ³ 1 byte Drive number. For example: ³

³ ³ Before open: 00h = default drive ³

³ ³ 01h = drive A: ³

³ ³ 02h = drive B: etc. ³

³ ³ After open: 00h = drive C: ³

³ ³ 01h = drive A: ³

³ ³ 02h = drive B: etc. ³

³ ³ An 0 is replaced by the actual drive number during open. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1-8 ³ 8 bytes Filename, left justified with blanks. If a reserved device ³

³ ³ name is placed here (such as PRN) do not include the optional colon. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 9-B ³ 3 bytes Filename extension, left justified with trailing blanks. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ C-D ³ 2 bytes Current block # relative to start of file, starting with 0 ³

³ ³ (set to 0 by the open function call). A block consists of 128 ³

³ ³ records, each of the size specified in the logical record size field.³

³ ³ The current block number is used with the current record field ³

³ ³ (below) for sequential reads and writes. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ E-F ³ 2 bytes Logical record size in bytes. Set to 80h by OPEN function ³

³ ³ If this is not correct, you must set the value because DOS uses it ³

³ ³ to determine the proper locations in the file for all disk reads and ³

³ ³ writes. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 10-13 ³ 4 bytes File size in bytes. In this field, the first word is the ³

³ ³ low-order part of the size. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 14-15 ³ 2 bytes Date file was created or last updated. mm/dd/yy are mapped ³

³ ³ as follows: ³

³ ³ 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 ³

³ ³ y y y y y y y m m m m d d d d d ³

³ ³ where: mm is 1-12 ³

³ ³ dd is 1-31 ³

³ ³ yy is 0-119 (1980-2099) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 16-17 ³ 2 bytes time file was created or last updated. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ These bytes contain the time when the file was created or last ³

³ ³ updated. The time is mapped in the bits as follows: ³

³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³

³ ³ B Y T E 16h ³ B Y T E 17h ³ ³

³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´ ³

³ ³ F E D C B A 9 8 ³ 7 6 5 4 3 2 1 0 ³ ³

³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´ ³

³ ³ H H H H H ³ M M M M M M ³ D D D D D ³ ³

³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´ ³

³ ³ binary # hrs 0-23 ³ binary # minutes 0-59 ³ bin. # 2-sec incr ³ ³

³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³

³ ³ note: The time is stored with the least significant byte first. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 18-19 ³ 2 bytes Reserved for DOS. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 20 ³1 byte Current relative record number (0-127) within the current ³

³ ³ block. This field and the Current Block field at offset 0Ch make up ³

³ ³ the record pointer. This field is not initialized by the OPEN ³

³ ³ function call. You must set this field before doing sequential read- ³

³ ³ write operations to the diskette. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 21-25 ³ 4 bytes Relative Record. Points to the currently selected record, ³

³ ³ counting from the beginning of the file starting with 0. This field ³

³ ³ is not initialized by the OPEN system call. You must set this field ³

³ ³ before doing a random read or write to the file. ³

³ ³ If the record size is less than 64 bytes, both words are used. ³

³ ³ Otherwise, only the first 3 bytes are used. Note that if you use the ³

³ ³ File Control Block at 5Ch in the program segment, the last byte of ³

³ ³ the FCB overlaps the first byte of the unformatted parameter area. ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

note 1) An unopened FCB consists of the FCB prefix (if used), drive number, and

filename.ext properly filled in. An open FCB is one in which the

remaining fields have been filled in by the CREAT or OPEN function

calls.

2) Bytes 0-5 and 32-36 must be set by the user program. Bytes 16-31 are set

by DOS and must not be changed by user programs.

3) All word fields are stored with the least significant byte first. For

example, a record length of 128 is stored as 80h at offset 14, and 00h

at offset 15.

EXTENDED FILE CONTROL BLOCKÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The extended file control block is used to create or search for files in the

disk directory that have special attributes.

It adds a 7 byte prefix to the FCB, formatted as follows:

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ E X T E N D E D F I L E C O N T R O L B L O C K ³

ÃÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ Bytes ³ Function ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0 ³ Flag byte containing 0FFh to indicate an extended FCB. ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1-6 ³ Reserved ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 6-7 ³ Attribute byte. Refer to function call 11h (search first) for ³

³ ³ details on using the attribute bits during directory searches. This ³

³ ³ function is present to allow applications to define their own files ³

³ ³ as hidden (and thereby excluded from normal directory searches) and ³

³ ³ to allow selective directory searches. ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

Any reference in the DOS function calls to an FCB, whether opened or unopened,

may use either a normal or extended FCB. If you are using an extended FCB, the

appropriate register should be set to the first byte of the prefix, rather than

the drive-number field.

Common practice is to refer to the extended FCB as a negative offset from the

first byte of a standard File Control Block.

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

C H A P T E R E I G H T

DOS DISK INFORMATION

THE DOS AREAÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

All disks and diskettes formatted by DOS are created with a sector size of 512

bytes. The DOS area (entire area for a diskette, DOS partition for hard disks)

is formatted as follows:

partition table - variable size (hard disk only)

boot record - 1 sector

first copy of the FAT - variable size

second copy of the FAT - same size as first copy

root directory - variable size

data area - variable depending on disk size

The following sections describe each of the allocated areas:

THE BOOT RECORDÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The boot record resides on track 0, sector 1, side 0 of every diskette

formatted by the DOS FORMAT program. For hard disks the boot record resides on

the first sector of the DOS partition. It is put on all disks to provide an

error message if you try to start up with a nonsystem disk in drive A:. If the

disk is a system disk, the boot record contains a JMP instruction pointing to

the first byte of the operating system.

If the device is IBM compatible, it must be true that the first sector of the

first FAT is located at the same sector for all possible media. This is

because the FAT sector is read before the media is actually determined.

The information relating to the BPB for a particular media is kept in the boot

sector for the media. In particular, the format of the boot sector is:

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ D O S B O O T R E C O R D ³

ÃÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³00h³3 bytes³ JMP to executable code. For DOS 2.x, 3 byte near jump (0E9h). ³

³ ³ ³ For DOS 3.x, 2 byte near jump (0EBh) followed by a NOP (90h) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³03h³8 bytes³ optional OEM name and version (such as IBM 2.1) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³0Bh³2 bytes³ bytes per sector ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³0Dh³ byte ³ ³ sectors per allocation unit (must be a power of 2) ³

ÃÄÄÄÅÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³0Eh³2 bytes³ B ³ reserved sectors (starting at logical sector 0) ³

³ ³ ³ ³ 01 for 1.x-3.31, 02 for 4.0+ ³

ÃÄÄÄÅÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³10h³ byte ³ ³ number of FATs ³

ÃÄÄÄÅÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³11h³2 bytes³ ³ maximum number of root directory entries ³

ÃÄÄÄÅÄÄÄÄÄÄÄ´ P ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³13h³2 bytes³ ³ number of sectors in logical image (total number of ³

³ ³ ³ ³ sectors in media, including boot sector directories, etc.)³

³ ³ ³ ³ If logical disk size is geater than 32Mb, this value is 0 ³

³ ³ ³ ³ and the actual size is reported at offset 26h (DOS 4.0+) ³

ÃÄÄÄÅÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³15h³ byte ³ B ³ media descriptor byte ³

ÃÄÄÄÅÄÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³16h³2 bytes³ ³ number of sectors occupied by a single FAT ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³18h³2 bytes³ sectors per track ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³1Ah³2 bytes³ number of heads ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³1Ch³2 bytes³ # of hidden sectors (sectors before this volume) (1st part) ³

ÀÄÄÄÁÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ EXTENDED BOOT RECORD (DOS 4.0+) ³

ÚÄÄÄÂÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³1Eh³2 bytes³ # of hidden sectors (sectors before this volume) (2nd part) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³20h³4 bytes³ # sectors in this disk (see offset 13h, if 0) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³24h³2 bytes³ physical drive number (max 2 for DOS 4, max 8 for DOS 5) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³26h³ byte ³ extended boot record signature (29h) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³27h³4 bytes³ volume serial number (assigned with a random function) ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³2Bh³11 byte³ volume label ³

ÃÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³36h³7 bytes³ file system ID (FAT12 ), (FAT16 ) etc. ("reserved") ³

ÀÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

The three words at the end return information about the media. The number of

heads is useful for supporting different multihead drives that have the same

storage capacity but a different number of surfaces. The number of hidden

sectors is useful for drive partitioning schemes.

DOS 3.2 uses a table called the BIOS Parameter Block (BPB) to determine if a

disk has a valid File Allocation Table. The BPB is located in the first sector

of a floppy disk. Although the BPB is supposed to be on every formatted floppy

disk, some earlier versions of DOS did not create a BPB and instead assumed that

the FAT begins at the second sector of the disk and that the first FAT byte

(Media Descriptor Byte) describes the disk format.

DOS 3.2 reads in the whole of the BPB and tries to use it - although,

strangely enough, it seems as if DOS is prepared to cope with a BPB that is

more or less totally blank (it seems to ignore the descriptor byte and treat it

as a DSDD 9-sector disk).

DOS 3.2 determines if a disk has a valid boot sector by examining the first

byte of logical sector 0. If that byte it a jump instruction E9h, DOS 3.2

assumes the rest of the sector is a valid boot sector with a BPB. If the first

byte is not E9h DOS 3.2 behaves like previous versions, assumes the boot sector

is invalid and uses the first byte of the FAT to determine the media type.

If the first byte on the disk happens to be E9h, but the disk does not have a

BPB, DOS 3.2 will return a disk error message.

The real problems occur if some of the BPB data is valid and some isn't.

Apparently some OEMs have assumed that DOS would continue to ignore the

formatting data on the disk, and have failed to write much there during FORMAT

except the media descriptor byte (or, worse, have allowed random junk to be

written there). While this error is understandable, and perhaps even

forgiveable, it remains their problem, not IBMs, since the BPB area has always

been documented as containing the format information that IBM DOS 3.2 now

requires to be there.

THE DOS FILE ALLOCATION TABLE (FAT)ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The File Allocation Table, or FAT, has three pain purposes:

1) to mark bad sectors on the media

2) to determine which sectors are free for use

3) to determine the physical location(s) of a file on the media.

DOS uses one of four different schemes for defining the File Allocation Table:

1) the 12-bit FAT, for DOS 1.x, 2.x, all floppies, and small hard disks

2) the 16-bit FAT, for DOS 3.x+ hard disks from 16.8 to 32Mb

3) the 32-bit FAT used by Compaq DOS 3.31 and others

4) the 32-bit FAT used by DOS 4.0 over-32Mb logical drives

This section explains how DOS uses the FAT to convert the clusters of a file

into logical sector numbers. We recommend that system utilities use the DOS

handle calls rather than interpreting the FAT.

The FAT is used by DOS to allocate disk space for files, one cluster at a time.

In DOS 4.0, clusters are referred to as "allocation units." It means the same

things; the smallest logical portion of a drive.

The FAT consists of a 12 bit entry (1.5 bytes) for each cluster on the disk or

a 16 bit (2 bytes) entry when a hard disk has more than 20740 sectors as is the

case with fixed disks larger than 10Mb.

The first two FAT entries map a portion of the directory; these FAT entries

contain indicators of the size and format of the disk. The FAT can be in a 12

or 16 bit format. DOS determines whether a disk has a 12 or 16 bit FAT by

looking at the total number of allocation units on a disk. For all diskettes

and hard disks with DOS partitions less than 20,740 sectors, the FAT uses a 12

bit value to map a cluster. For larger partitions, DOS uses a 16 bit value.

The second, third, and fourth bit applicable for 16 bit FAT bytes always

contains 0FFFFh. The first byte is used as follows:

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ M E D I A D E S C R I P T O R B Y T E ³

ÃÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³hex value ³ meaning ³ normally used ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F0 ³ double sided 18 sector diskette ³ PS/2 1.44 meg DSHD ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F8 ³ hard disk ³ bootable hard disk at C:800 ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F9 ³ double sided 15 sector diskette ³ AT 1.2 meg DSHD ³

³ ³ double sided 9 sector diskette ³ Convertible 720k DSQD ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FA ³ IBM Displaywriter System disk ³ 287k ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FB ³ IBM Displaywriter System disk ³ 1 meg ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FC ³ single sided 9 sector diskette ³ DOS 2.0, 180k SSDD ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FD ³ double sided 9 sector diskette ³ DOS 2.0, 360k DSDD ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FE ³ single sided 8 sector diskette ³ DOS 1.0, 160k SSDD ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FF ³ double sided 8 sector diskette ³ DOS 1.1, 320k SSDD ³

ÃÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

³for 8 inch diskettes: ³

ÃÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ FD ³ double sided 26 sector diskette ³ IBM 3740 format DSSD ³

ÃÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ FE ³ single sided 26 sector diskette ³ IBM 3740 format SSSD ³

³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ ³ double sided 8 sector diskette ³ IBM 3740 format DSDD ³

ÀÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

The third FAT entry begins mapping the data area (cluster 002).

NOTE: These values are provided as a reference. Therefore, programs should not

make use of these values.

Each entry contains a hexadecimal character (or 4 for 16 bit FATs). ()

indicates the high order four bit value in the case of 16 bit FAT entries.

They can be:

(0)000h if the cluster is unused and availible

(0F)FF8h - (0F)FFFh to indicate the last cluster of a file

(X)XXXh any other hexadecimal numbers that are the cluster number

of the next cluster in the file. The cluster number is the

first cluster in the file that is kept in the file's

directory entry.

The values (0F)FF0h - (0F)FF7h are used to indicate reserved clusters.

(0F)FF7h indicates a bad cluster if it is not part of the allocation chain.

(0F)FF8h - (0F)FFFh are used as end of file markers.

The file allocation table always occupies the sector or sectors immediately

following the boot record. If the FAT is larger than 1 sector, the sectors

occupy consecutive sector numbers. Two copies of the FAT are written, one

following the other, for integrity. The FAT is read into one of the DOS buffers

whenever needed (open, allocate more space, etc).

USE OF THE 12 BIT FILE ALLOCATION TABLEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Obtain the starting cluster of the file from the directory entry.

Now, to locate each subsequent sector of the file:

1. Multiply the cluster number just used by 1.5 (each FAT entry is 1.5

bytes long).

2. The whole part of the product is offset into the FAT, pointing to the entry

that maps the cluster just used. That entry contains the cluster number of

the next cluster in the file.

3. Use a MOV instruction to move the word at the calculated FAT into a register.

4. If the last cluster used was an even number, keep the low order 12 bits of

the register, otherwise, keep the high order 12 bits.

5. If the resultant 12 bits are (0FF8h-0FFFh) no more clusters are in the file.

Otherwise, the next 12 bits contain the cluster number of the next cluster in

the file.

To convert the cluster to a logical sector number (relative sector, such as

that used by int 25h and 26h and DEBUG):

1. Subtract 2 from the cluster number

2. Multiply the result by the number of sectors per cluster.

3. Add the logical sector number of the beginning of the data area.

12-bit FAT if DOS partition is smaller than 32,680 sectors (16.340 MB).

USE OF THE 16 BIT FILE ALLOCATION TABLEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Obtain the starting cluster of the file from the directory entry. Now to

locate each subsequent cluster of the file:

1. Multiply the cluster number used by 2 (each FAT entry is 2 bytes long).

2. Use the MOV word instruction to move the word at the calculated FAT offset

into a register.

3. If the resultant 16 bits are (0FF8h-0FFFFh) no more clusters are in the

file. Otherwise, the 16 bits contain the cluster number of the next cluster

in the file.

Compaq DOS makes availible a new disk type (6) with 32 bit partition values,

allowing 512 megabytes per hard disk (Compaq DOS 3.3.1)

DOS DISK DIRECTORYÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The FORMAT command initially builds the root directory for all disks. Its

location (logical sector number) and the maximum number of entries are

availible through the device driver interfaces.

Since directories other than the root directory are actually files, there is

no limit to the number of entries that they may contain.

All directory entries are 32 bytes long, and are in the following format:

ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ BYTES ³ DISK DIRECTORY ENTRY

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 0-7 ³ 8 bytes filename

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ The first byte of the filename indicates the file status.

³ The file status byte can contain the following values:

ÃÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 00h ³ Directory entry has never been used. This is used to limit

³ ³ the length of directory searches, for performance reasons.

³ 05h ³ Indicates that the first character of the filename actually

³ ³ has an 0EDh character.

³ 0E5h ³ Filename has been used but the file has been erased.

³ 2Eh ³ This entry is for a directory. If the second byte is also

³ ³ 2Eh, the cluster field contains the cluster number of this

³ ³ directory's parent directory. (0000h if the parent directory

³ ³ is the root directory).

ÃÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ Any other character is the first character of a filename. Filenames

³ are left-aligned and if nescessary padded with blanks.

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 8-A ³ 3 bytes filename extension if any

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ Three characters, left-aligned and padded with blanks if nescessary.

³ If there is no file extension, this field contains all blanks

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ B ³ 1 byte file attributes

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ The attribute byte is mapped as follows:

ÃÄÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ hex ³bit³ meaning

ÃÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 00h ³ ³ (no bits set) normal; can be read or written w/o restriction

³ 01h ³ 0 ³ file is marked read-only. An attempt to open the file for

³ ³ ³ output using function call 3Dh will fail and an error code

³ ³ ³ will be returned. This value can be used with other values

³ ³ ³ below.

³ 02h ³ 1 ³ indicates a hidden file. The file is excluded from normal

³ ³ ³ directory searches.

³ 04h ³ 2 ³ indicates a system file. This file is excluded from normal

³ ³ ³ directory searches.

³ 08h ³ 3 ³ indicates that the entry contains the volume label in the

³ ³ ³ first 11 bytes. The entry has no other usable information

³ ³ ³ and may exist only in the root directory.

³ 10h ³ 4 ³ indicates that the file is a subdirectory

³ 20h ³ 5 ³ indicates an archive bit. This bit is set on whenever the

³ ³ ³ file is written to and closed. Used by BACKUP and RESTORE.

³ ³ 6 ³ reserved

³ ³ 7 ³ reserved

ÃÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ Bits 6 and 7 are reserved, and must be 0. They may be used in OS/2.

³ note: Attributes 08h and 10h cannot be changed using int21/43h.

³ The system files IBMBIO.COM and IBMDOS.COM (or customized equivalent)

³ are marked as read-only, hidden, and system files. Files can be

³ marked hidden when they are created. Also, the read-only, hidden,

³ system and archive attributes may be changed with int21/43h.

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 0C-15 ³ 10 bytes reserved by DOS; value unknown

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 16-17 ³ 2 bytes file timestamp

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ These bytes contain the time when the file was created or last

³ updated. The time is mapped in the bits as follows:

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ B Y T E 16h ³ B Y T E 17h ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F E D C B A 9 8 ³ 7 6 5 4 3 2 1 0 ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ H H H H H ³ M M M M M M ³ D D D D D ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ binary # hrs 0-23 ³ binary # minutes 0-59 ³ bin. # 2-sec incr ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

³ note: The time is stored with the least significant byte first.

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 18-19 ³ 2 bytes file datestamp

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ This area contains the date when the file was created or last

³ updated. The mm/dd/yy are mapped in the bits as follows:

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ B Y T E 18h ³ B Y T E 19h ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ F E D C B A 9 8 ³ 7 6 5 4 3 2 1 0 ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ Y Y Y Y Y Y Y ³ M M M M ³ D D D D D ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0-119 (1980-2099) ³ 1-12 ³ 1-31 ³

ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

³ note: The time is stored with the least significant byte first.

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 1A-1B ³ 2 bytes first file cluster number

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ * (reserved in DOS 2, documented in DOS 3+)

³ This area contains the starting cluster number of the first cluster

³ in the file. The first cluster for data space on all fixed disks and

³ floppy disks is always cluster 002. The cluster number is stored

³ with the least significant byte first.

ÚÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ 1C-1F ³ 4 bytes filesize

ÀÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

³ This area contains the file size in bytes. The first word contains

³ the low order part of the size. Both words are stored with the least

³ significant byte first.

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

THE DATA AREAÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Allocation of space for a file (in the data area) is done only when needed

(it is not preallocated). The space is allocated one cluser (unit allocation)

at a time. A cluster is always one or more consecutive sector numbers, and all

of the clusters in a file are "chained" together in the FAT.

The clusters are arranged on disk to minimize head movement for multisided

media. All of the space on a track (or cylinder) is allocated before moving

on to the next track. This is accomplished by using the sequential sector

numbers on the lowest-numbered head, then all the sector numbers on the next

head, and so on until all sectors of all heads of the track are used. Then the

next sector used will be sector 1 of head 0 on the next track.

An interesting innovation that was introduced in MS-DOS 3.0: disk space that

is freed by erasing a file is not re-used immediately, unlike earlier versions

of DOS. Instead, free space is obtained from the area not yet used during the

current session, until all of it is used up. Only then will space that is freed

during the current session be re-used.

This feature minimizes fragmentation of files, since never-before-used space

is always contiguous. However, once any space has been freed by deleting a file,

that advantage vanishes at the next system boot. The feature also greatly

simplifies un-erasing files, provided that the need to do an un-erase is found

during the same session and also provided that the file occupies contiguous

clusters.

However, when one is using programs which make extensive use of temporary

files, each of which may be created and erased many times during a session,

the feature becomes a nuisance; it forces the permanent files to move farther

and farther into the inner tracks of the disk, thus increasing rather than

decreasing the amount of fragmentation which occurs.

The feature is implemented in DOS by means of a single 16-bit "last cluster

used" (LCU) pointer for each physical disk drive; this pointer is a part of

the physical drive table maintained by DOS. At boot time, the LCU pointer is

zeroed. Each time another cluster is obtained from the free-space pool (the

FAT), its number is written into the LCU pointer. Each time a fresh cluster

is required, the FAT is searched to locate a free one; in older versions of

DOS this search always began at Cluster 0000, but in 3.x it begins at the

cluster pointed to by the LCU pointer.

For hard disks, the size of the file allocation table and directory are

determined when FORMAT initializes it and are based on the size of the DOS

partition.

Files in the data area are not nescessarily written sequentially on the first.

The data area space is allocated one cluster at a time, skipping over clusters

already allocated. The first free cluster found is the next cluster allocated,

regardless of its physical location on the disk. This permits the most efficient

utilization of disk space because clusters freed by erasing files can be

allocated for new files. Refer back to the description of the DOS FAT in this

chapter for more information.

SSDD single sided, double density (160-180k) 5¬

DSDD double sided, double density (320-360k) 5¬

DSQD double sided, quad density (720k) 5¬, 3«

DSHD double sided, high density (1.2-1.44M) 5¬, 3«

Much of the trouble with AT 1.2 meg drives has been through the inadverdent

use of quad density disks in the high density drives. The high density disks

use a higher-coercivity media than the quads, and quads are not completely

reliable as 1.2M. Make sure you have the correct disk for your application.

HARD DISK LAYOUTÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The DOS hard disk routines perform the following services:

1) Allow multiple operating systems to utilize the hard disk without the need

to backup and restore files when changing operating systems.

2) Allow a user-selected operating system to be started from the hard disk.

I) In order to share the hard disk among operating systems, the disk may be

logically divided into 1 to 4 partitions. The space within a given

partition is contiguous, and can be dedicated to a specific operating

system. Each operating system may "own" only one partition in DOS versions

2.0 through 3.2. PCDOS 3.3 introduced the "Extended DOS Partition" which

allows multiple DOS partitions on the same hard disk. The FDISK.COM (or

similar program from other DOS vendors) utility allows the user to select

the number, type, and size of each partition. The partition information is

kept in a partition table that is embedded in the master fixed disk boot

record on the first sector of the disk. The format of this table varies

from version to version of DOS.

II) An operating system must consider its partition to be the entire disk,

and must ensure that its functions and utilities do not access other

partitions on the disk.

III) Each partition may contain a boot record on its first sector, and any

other programs or data that you choose - including a copy of an operating

system. For example, the DOS FORMAT command may be used to format and

place a copy of DOS in the DOS partition in the same manner that a

diskette is formatted. With the FDISK utility, you may designate a

partition as "active" (bootable). The master hard disk boot record causes

that partition's boot record to receive control when the system is started

or reset. Additional disk partitions could be FORTH, UNIX, Pick, CP/M-86,

or the UCSD p-System.

SYSTEM INITIALIZATIONÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

The boot sequence is as follows:

1. System initialization first attempts to load an operating system from

diskette drive A. If the drive is not ready or a read error occurs, it then

attempts to read a master hard disk boot record on the first sector of the

first hard disk in the system. If unsuccessful, or if no hard disk is

present, it invokes ROM BASIC in an IBM PC or displays a disk error

message on most compatibles.

2. If initialization is successful, the master hard disk boot record is given

control and it examines the partition table embedded within it. If one of

the entries indicates an active (bootable) partition, its boot record is

read from the partition's first sector and given control.

3. If none of the partitions is bootable, ROM BASIC is invoked on an IBM PC or

a disk error on most compatibles.

4. If any of the boot indicators are invalid, or if more than one indicator is

marked as bootable, the message INVALID PARTITION TABLE is displayed and the

system stops.

5. If the partition's boot record cannot be successfully read within five

retries due to read errors, the message ERROR LOADING OPERATING SYSTEM

appears and the system stops.

6. If the partition's boot record does not contain a valid "signature", the

message MISSING OPERATING SYSTEM appears, and the system stops.

NOTE: When changing the size or location of any partition, you must ensure that

all existing data on the disk has been backed up. The partitioning program

will destroy the data on the disk.

System programmers designing a utility to initialize/manage a hard disk must

provide the following functions at a minimum:

1. Write the master disk boot record/partition table to the disk's first

sector to initialize it.

2. Perform partitioning of the disk-that is, create or update the partition

table information (all fields for the partition) when the user wishes

to create a partition. This may be limited to creating a partition for only

one type of operating systewm, but must allow repartitoning the entire disk,

or adding a partition without interfering with existing partitions (user's

choice).

3. Provide a means for marking a user-specified partition as bootable and

resetting the bootable indicator bytes for all other partitions at the same

time.

4. Such utilities should not change or move any partition information that

belongs to another operating system.

BOOT RECORD/PARTITION TABLEÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

A boot record must be written on the first sector of all hard disks, and

must contain the following:

1. Code to load and give control to the boot record for one of four possible

operating systems.

2. A partition table at the end of the boot record. Each table entry is 16

bytes long, and contains the starting and ending cylinder, sector, and head

for each of four possible partitions, as well as the number of sectors

preceding the partition and the number of sectors occupied by the partition.

The "boot indicator" byte is used by the boot record to determine if one of

the partitions contains a loadable operating system. FDISK initialization

utilities mark a user-selected partition as "bootable" by placing a value

of 80h in the corresponding partition's boot indicator (setting all other

partitions' indicators to 0 at the same time). The presence of the 80h tells

the standard boot routine to load the sector whose location is contained in

the following three bytes. That sector is the actual boot record for the

selected operating system, and it is responsible for the remainder of the

system's loading process (as it is from the diskette). All boot records are

loaded at absolute address 0:7C00.

The partition table with its offsets into the boot record is:

(except for Wyse DOS 3.2 with 32 bit allocation table, and DOS 3.3-up)

ÚÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ¿

³Offset³Partit'n³ Purpose ³ ³ Head ³ Sector ³ Cylinder ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ´

³ 1BEh ³ part 1 ³ begin ³ boot ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ´

³ 1C2h ³ ³ end ³ syst ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ´

³ 1C6h ³ ³ relative sector ³ low word ³ high word ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1CAh ³ ³ # sectors ³ low word ³ high word ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ´

³ 1CEh ³ part 2 ³ begin ³ boot ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ´

³ 1D2h ³ ³ end ³ syst ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ´

³ 1D6h ³ ³ relative sector ³ low word ³ high word ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1DAh ³ ³ # sectors ³ low word ³ high word ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ´

³ 1DEh ³ part 3 ³ begin ³ boot ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ´

³ 1E2h ³ ³ end ³ syst ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ´

³ 1E6h ³ ³ relative sector ³ low word ³ high word ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1EAh ³ ³ # sectors ³ low word ³ high word ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ´

³ 1EEh ³ part 4 ³ begin ³ boot ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ´

³ 1F2h ³ ³ end ³ syst ind ³ H ³ S ³ cyl ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ´

³ 1F6h ³ ³ relative sector ³ low word ³ high word ³

ÃÄÄÄÄÄÄ´ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 1FAh ³ ³ # sectors ³ low word ³ high word ³

ÃÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

³ 1FEh ³ signature ³ hex 55 ³ hex AA ³

ÀÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÙ

Boot indicator (boot ind): The boot indicator byte must contain 0 for a non-

bootable partition or 80h for a bootable partition. Only one partition can be

marked as bootable at a time.

System Indicator (sys ind): The sys ind field contains an indicator of the

operating system that "owns" the partition. IBM PC-DOS can only "own" one

partition, though some versions of MSDOS allow all four partitions to be used

by DOS.

The system indicators are:

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³ System Indicator (sys ind) ³

ÃÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 00h ³ unknown or unspecified ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 01h ³ DOS 12 bit FAT (DOS 2.x all and 3.x under 10 Mb) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 04h ³ DOS 16 bit FAT (DOS 3.x+. Not recognized by 2.x) ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0DBh ³ DRI Concurrent DOS ³

ÃÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´

³ 0F2h ³ 2nd DOS partition, some 3.2 and all 3.3 ³

ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

There are bytes for XENIX, and other operating systems. Some manufacturers

(such as Zenith, Wyse, and Tandon) diddle with these system bytes to implement

more than one DOS partition per disk.

Cylinder (CYL) and Sector (S): The 1 byte fields labelled CYL contain the low

order 8 bits of the cylinder number - the high order 2 bits are in the high

order 2 bits of the sector (S) field. This corresponds with the ROM BIOS

interrupt 13h (disk I/O) requirements, to allow for a 10 bit cylinder number.

The fields are ordered in such a manner that only two MOV instructions are

required to properly set up the DX and CX registers for a ROM BIOS call to

load the appropriate boot record (hard disk booting is only possible from the

first hard disk in the system, where a BIOS drive number of 80h corresponds

to the boot indicator byte).

All partitions are allocated in cylinder multiples and begin on sector 1,

head 0, with the exception that the partition that is allocated at the beginning

of the disk starts at sector 2, to account for the hard disk's master boot

record.

Relative Sector (rel sect): The number of sectors preceding each partition

on the disk is kept in the 4 byte field labelled "rel sect". This value is

obtained by counting the sectors beginning with cylinder 0, sector 1, head 0

of the disk, and incrementing the sector, head, and then track values up to

the beginning of the partition. This, if the disk has 17 sectors per track and

4 heads, and the second partition begins at cylinder 1, sector 1, head 0,and

the partition's starting relative sector is 68 (decimal) - there were 17

sectors on each of 4 heads on 1 track allocated ahead of it. The field is stored

with the least significant word first.

Number of sectors (#sects): The number of sectors allocated to the partition

is kept in the "# of sects" field. This is a 4 byte field stored least

significant word first.

Signature: The last 2 bytes of the boot record (55AAh) are used as a signature

to identify a valid boot record. Both this record and the partition boot record

are required to contain the signature at offset 1FEh.

HARD DISK TECHNICAL INFORMATIONÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Western Digital's hard disk installation manuals make the claim that MSDOS

can support only 2 hard drives. This is entirely false, and their purpose for

making the claim is unclear. DOS merely performs a function call pointed at

the hard disk driver, which is normally in one of three locations; a ROM at

absolute address C:800, the main BIOS ROM if the machine is an AT, or a device

driver installed through the CONFIG.SYS file. Two hard disk controller cards

can normally not reside in the same machine due to lack of interrupt

arbitration. Perstor's ARLL controller and some cards marketed by Novell can

coexist with other controllers. Perstor's technical department has had four

controllers and eight hard disks in the same IBM XT functioning concurrently.

A valid hard disk has a boot record arranged in the following manner:

DB drive ; 0 or 80h (80h marks a bootable, active partition)

DB head1 ; starting heads

DW trksec1 ; starting track/sector (CX value for INT 13)

DB system ; see below

DB head2 ; ending head

DW trksec2 ; ending track/sector

DD sector1 ; absolute # of starting sector

DD sector2 ; absolute # of last sector

The master disk boot record invokes ROM BASIC if no indicator byte reflects a

bootable system.

When a partition's boot record is given control, it is passed its partition

table entry address in the DS:SI registers.

DETERMINING FIXED DISK ALLOCATIONÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

DOS determines disk allocation using the following formula:

D * BPD

TS - RS - ÄÄÄÄÄÄÄÄÄÄÄ

BPS

SPF = ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

BPS * SPC

CF + ÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

BPC

where:

TS total sectors on disk

RS the number of sectrs at the beginning of the disk that are reserved

for the boot record. DOS reserves 1 sector.

D The number of directory entries in the root directory.

BPD the number of bytes per directory entry. This is always 32.

BPS the number of bytes per logical sector. Typically 512, but you can

specify a different number with VDISK.

CF The number of FATS per disk. Usually 2. VDISK is 1.

SPF the number of sectors per FAT. Maximum 64.

SPC The number of sectors per allocation unit.

BPC the number of bytes per FAT entry. BPC is 1.5 for 12 bit FATs.

2 for 16 bit FATS.

To calculate the minimum partition size that will force a 16-bit FAT:

CYL = (max clusters * 8)/(HEADS * SPT)

where:

CYL number of cylinders on the disk

max clusters 4092 (maximum number of clusters for a 12 bit FAT)

HEADS number of heads on the hard disk

SPT sectors per track (normally 17 on MFM)

DOS 2.0 uses a "first fit" algorithm when allocating file space on the hard

disk. Each time an application requests disk space, it will scan from the

beginning of the FAT until it finds a contiguous piece of storage large enough

for the file.

DOS 3.0 keeps a pointer into the disk space, and begins its search from the

point it last left off. This pointer is lost when the system is rebooted.

This is called the "next fit" algorithm. It is faster than the first fit and

helps minimize fragmentation.

In either case, if the FCB function calls are used instead of the handle

function calls, the file will be broken into pieces starting with the first

availible space on the disk.

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

The rest of the chapters aren't included in this shareware demonstration

package. Since the complete manual takes almost a megabyte archived,

something had to give somewhere.

Here's a sample of what you're missing:

DOS 5 information (mainly in registered chapter 4, some in 5)

(Chapters 1 and 2 are complete)

CHAPTER 3 The IBM ROM BIOS

Calling the ROM BIOS .................................................. 3**1

Interrupt 10h Video Services ......................................... 3**2

Interrupt 11h Equipment Check ........................................ 3**3

Interrupt 12h Memory Size ............................................ 3**4

Interrupt 13h Disk Functions ......................................... 3**5

Interrupt 14h Initialize and Access Serial Port ...................... 3**6

FOSSIL Drivers ......................................... 3**7

Interrupt 15h Cassette I/O ........................................... 3**8

Interrupt 16h Keyboard I/O ........................................... 3**9

Interrupt 17h Printer ................................................ 3**10

Interrupt 18h ROM BASIC .............................................. 3**11

Interrupt 19h Bootstrap Loader ....................................... 3**12

Interrupt 1Ah Time of Day ............................................ 3**13

Interrupt 1Bh Control-Break .......................................... 3**14

Interrupt 1Ch Timer Tick ............................................. 3**15

Interrupt 1Dh Vector of Video Initialization Parameters .............. 3**16

Interrupt 1Eh Vector of Diskette Controller Parameters ............... 3**17

Interrupt 1Fh Ptr to Graphics Character Extensions (Graphics Set 2) .. 3**18

CHAPTER 4 DOS Function Requests

General Programming Guides ............................................ 4**1

DOS Registers ......................................................... 4**2

DOS Stacks ............................................................ 4**3

DOS Interrupts ........................................................ 4**4

Interrupt 20h (Terminate) ............................................. 4**5

DOS Services (quick list) ............................................. 4**6

Calling the DOS Services .............................................. 4**7

Version Specific Information .......................................... 4**8

Compatibility Problems With DOS 4.0+ .................................. 4**9

PCjr Cartridge Support ................................................ 4**10

eDOS 4.0 .............................................................. 4**11

DOS Services in Detail ................................................ 4**12

CHAPTER 5 Interrupts 22h through 0FFh

Interrupt 22h Terminate Address ..................................... 5**1

Interrupt 23h Ctrl-Break Exit Address ............................... 5**2

Interrupt 24h Critical Error Handler ................................ 5**3

Interrupt 25h Absolute Disk Read .................................... 5**4

Interrupt 26h Absolute Disk Write ................................... 5**5

Interrupt 27h Terminate And Stay Resident ........................... 5**6

Interrupt 28h (not documented by Microsoft) ......................... 5**7

Interrupt 29h (not documented by Microsoft) ......................... 5**8

Interrupt 2Ah Microsoft Networks - Session Layer Interrupt .......... 5**9

Interrupt 2Bh Unknown ............................................... 5**10

Interrupt 2Ch Unknown ............................................... 5**11

Interrupt 2Dh Unknown ............................................... 5**12

Interrupt 2Eh Alternate EXEC (DOS 2.0+) ............................. 5**13

Interrupt 2Fh Multiplex Interrupt ................................... 5**14

Interrupt 30h FAR jump instruction for CP/M-style calls ............. 5**15

Interrupt 31h Unknown ............................................... 5**16

Interrupt 32h Unknown ............................................... 5**17

Interrupt 33h Used by Microsoft Mouse Driver Function Calls ......... 5**18

Interrupt 34h Turbo C/Microsoft languages - Floating Point emulation 5**19

Interrupt 35h Turbo C/Microsoft languages - Floating Point emulation 5**20

Interrupt 36h Turbo C/Microsoft languages - Floating Point emulation 5**21

Interrupt 37h Turbo C/Microsoft languages - Floating Point emulation 5**22

Interrupt 38h Turbo C/Microsoft languages - Floating Point emulation 5**23

Interrupt 39h Turbo C/Microsoft languages - Floating Point emulation 5**24

Interrupt 3Ah Turbo C/Microsoft languages - Floating Point emulation 5**25

Interrupt 3Bh Turbo C/Microsoft languages - Floating Point emulation 5**26

Interrupt 3Ch Turbo C/Microsoft languages - Floating Point emulation 5**27

Interrupt 3Dh Turbo C/Microsoft languages - Floating Point emulation 5**28

Interrupt 3Eh Turbo C/Microsoft languages - Floating Point emulation 5**29

Interrupt 3Fh Overlay Manager Interrupt (Microsoft LINK.EXE) ........ 5**30

Interrupt 40h Hard Disk BIOS ........................................ 5**31

Interrupt 41h Hard Disk Parameters .................................. 5**32

Interrupt 42h Pointer to screen BIOS entry .......................... 5**33

Interrupt 43h Pointer to EGA Graphics Character Table ............... 5**34

Interrupt 44h Pointer to graphics character table ................... 5**35

Interrupt 45h Reserved by IBM (not initialized) .................... 5**36

Interrupt 46h Pointer to second hard disk parameter block ........... 5**37

Interrupt 47h Reserved by IBM (not initialized) .................... 5**38

Interrupt 48h Cordless Keyboard Translation ......................... 5**39

Interrupt 49h Non-keyboard Scan Code Translation Table Address (PCjr) 5**40

Interrupt 4Ah Real-Time Clock Alarm (Convertible, PS/2) ............. 5**41

Interrupt 4Bh Reserved by IBM (not initialized) .................... 5**42

Interrupt 4Ch Reserved by IBM (not initialized) .................... 5**43

Interrupt 4Dh Reserved by IBM (not initialized) .................... 5**44

Interrupt 4Eh Reserved by IBM (not initialized) .................... 5**45

Interrupt 4Fh Reserved by IBM (not initialized) .................... 5**46

Interrupt 50-57 IRQ0-IRQ7 Relocation .................................. 5**47

Interrupt 58h Reserved by IBM (not initialized) .................... 5**48

Interrupt 59h Reserved by IBM (not initialized) .................... 5**49

Interrupt 5Ah Reserved by IBM (not initialized) ................... 5**50

Interrupt 5Bh Reserved by IBM (not initialized) .................... 5**51

Interrupt 5Ah Cluster Adapter BIOS entry address .................... 5**52

Interrupt 5Bh Reserved by IBM (not initialized) .................... 5**53

Interrupt 5Ch NETBIOS interface entry port, TOPS .................... 5**54

Interrupt 5Dh Reserved by IBM (not initialized) .................... 5**55

Interrupt 5Eh Reserved by IBM (not initialized) .................... 5**56

Interrupt 5Fh Reserved by IBM (not initialized) .................... 5**57

Interrupt 60h-67h User Program Interrupts ............................ 5**58

Interrupt 60h Network OS Interface .................................. 5**59

Interrupt 67h Expanded Memory Board Driver Interrupt ................ 5**60

Interrupt 68h Not Used (not initialized) ........................... 5**61

Interrupt 69h Not Used (not initialized) ........................... 5**62

Interrupt 6Ah Not Used (not initialized) ........................... 5**63

Interrupt 6Bh Not Used (not initialized) ........................... 5**64

Interrupt 6Ch System Resume Vector (Convertible) .................... 5**65

Interrupt 6Dh Not Used (not initialized) ........................... 5**66

Interrupt 6Eh Not Used (not initialized) ........................... 5**67

Interrupt 6Fh 10-Net API............................................. 5**68

Interrupt 70h IRQ 8, Real Time Clock Interrupt (AT, XT/286, PS/2) ... 5**69

Interrupt 71h IRQ 9, Redirected to IRQ 8 (AT, XT/286, PS/2) ......... 5**70

Interrupt 72h IRQ 10 (AT, XT/286, PS/2) Reserved .................. 5**71

Interrupt 73h IRQ 11 (AT, XT/286, PS/2) Reserved .................. 5**72

Interrupt 74h IRQ 12 Mouse Interrupt (PS/2) ........................ 5**73

Interrupt 75h IRQ 13, Coprocessor Error (AT) ........................ 5**74

Interrupt 76h IRQ 14, Hard Disk Controller (AT, XT/286, PS/2) ....... 5**75

Interrupt 77h IRQ 15 (AT, XT/286, PS/2) Reserved ................... 5**76

Interrupt 78h Not Used .............................................. 5**77

Interrupt 79h Not Used .............................................. 5**78

Interrupt 7Ah Reserved .............................................. 5**79

Interrupt 7Bh-7Eh Not Used by IBM .................................... 5**80

Interrupt 7Ch REXX-PC API ........................................... 5**81

Interrupt 7Fh IBM 8514/A Graphics Adapter API ....................... 5**82

Interrupt 80h-85h Reserved by BASIC .................................. 5**83

Interrupt 86h Int 18 when relocated by NETBIOS ...................... 5**84

Interrupt 86h-0F0h Used by BASIC when BASIC interpreter is running ... 5**85

Interrupt 0A4h Right Hand Man API .................................... 5**86

Interrupt 0D4h PC-MOS/386 API ........................................ 5**87

Interrupt 0E0h Digital Research CP/M-86 function calls ............... 5**88

Interrupt 0E1h PC Cluster Disk Server Information .................... 5**89

Interrupt 0E2h PC Cluster Program .................................... 5**90

Interrupt 0E4h Logitech Modula-2 v2.0 Monitor Entry ................ 5**91

Interrupt 0E5h Not Used .............................................. 5**92

Interrupt 0E6h Not Used .............................................. 5**93

Interrupt 0E7h Not Used .............................................. 5**94

Interrupt 0E8h Not Used .............................................. 5**95

Interrupt 0E9h Not Used .............................................. 5**96

Interrupt 0EAh Not Used .............................................. 5**97

Interrupt 0EBh Not Used .............................................. 5**98

Interrupt 0ECh Not Used .............................................. 5**99

Interrupt 0EDh Not Used ............................................. 5**100

Interrupt 0EEh Not Used ............................................. 5**101

Interrupt 0EFh GEM interface (Digital Research) ..................... 5**102

Interrupt 0F0h unknown .............................................. 5**103

Interrupts 0F1h-0FFh (absolute addresses 3C4h-3FFh) ................. 5**104

Interrupt 0F4h Not Used ............ ................................ 5**105

Interrupt 0F5h Not Used ............ ................................ 5**106

Interrupt 0F8h Set Shell Interrupt (OEM) ............................ 5**107

Interrupt 0F9h Reserved ............................................. 5**108

Interrupt 0FAh USART ready (RS-232C) ................................ 5**109

Interrupt 0FBh USART RS ready (keyboard) ............................ 5**110

Interrupt 0FCh Unknown ...............................................5**111

Interrupt 0FDh reserved for user interrupt .......................... 5**112

Interrupt 0FEh reserved by IBM ...................................... 5**113

Interrupt 0FFh reserved by IBM ...................................... 5**114

CHAPTER 6 DOS Control Blocks and Work Areas

DOS Address Space ..................................................... 6**1

Storage Blocks ........................................................ 6**2

Disk Transfer Area (DTA) .............................................. 6**3

Program Segment Prefix ................................................ 6**4

Memory Control Blocks ................................................. 6**5

DOS Program Segment ................................................... 6**6

CHAPTER 7 DOS File Information

File Management Functions ............................................. 7**1

FCB Function Calls .................................................... 7**2

Handle Function Calls ................................................. 7**3

Special File Handles .................................................. 7**4

Raw and Cooked File I/O ............................................... 7**5

Number of Open Files Allowed ......................................... 7**6

Restrictions on FCB Usage ............................................. 7**7

Restrictions on Handle usage .......................................... 7**8

Allocating Space to a File ............................................ 7**9

MSDOS / PCDOS Differences ............................................. 7**10

.COM File Structure ................................................... 7**11

.EXE File Structure ................................................... 7**12

The Relocation Table .................................................. 7**13

"NEW" .EXE Format (Microsoft Windows and OS/2) ........................ 7**14

Standard File Control Block ........................................... 7**15

Extended File Control Block ........................................... 7**16

Disk Transfer Area .................................................... 7**17

CHAPTER 8 DOS Disk Information

The DOS Area .......................................................... 8**1

The Boot Record ....................................................... 8**2

DOS File Allocation Table (FAT) ....................................... 8**3

Media Descriptor Byte ......................................... 8**4

12 Bit FATs ................................................... 8**5

16 Bit FATs ................................................... 8**6

32 Bit FATs ................................................... 8**7

DOS Disk Directory .................................................... 8**8

The Data Area ......................................................... 8**9

Floppy Disk Types ..................................................... 8**10

Hard Disk Layout ...................................................... 8**11

System Initialization ................................................. 8**12

Boot Record/Partition Table ........................................... 8**13

Hard Disk Technical Information ....................................... 8**14

Determining Hard Disk File Allocation ................................. 8**15

BIOS Disk Functions ................................................... 8**16

CHAPTER 9 Device Drivers

CHAPTER 10 Lotus/Intel/Microsoft Expanded Memory Specification

History ............................................................... 10**1

Uses of Expanded Memory ............................................... 10**2

DOS and Expanded Memory ............................................... 10**3

Different Memory Types ................................................ 10**4

AST/Quadram/Ashton-Tate Enhanced EMM .................................. 10**5

EMS Address Space Map ................................................. 10**6

Writing Programs That Use Expanded Memory ............................. 10**7

Page Frames ........................................................... 10**8

Calling the Manager ................................................... 10**9

Detecting EMS ......................................................... 10**10

Terminate and Stay Resident (TSR) Program Cooperation ................. 10**11

Expanded Memory Services Quick List ................................... 10**12

Expanded Memory Services .............................................. 10**13

LIM 3.2 Specification ......................................... 10**14

LIM 4.0 Specification ......................................... 10**15

AQA EEMS 3.2 Specification .................................... 10**16

VCPI API 1.0 .................................................. 10**17

Expanded Memory Manager Error Codes ................................... 10**18

CHAPTER 11 Conversion Between Operating Systems

Overview .............................................................. 11**1

Special Considerations ................................................ 11**2

Example Operating Systems ............................................. 11**3

Atari ST .............................................................. 11**4

CP/M .................................................................. 11**5

MacOS ................................................................. 11**6

AmigaDOS .............................................................. 11**7

OS/2 .................................................................. 11**8

UNIX .................................................................. 11**9

CHAPTER 12 Microsoft Windows API

Overview .............................................................. 12**1

Programming Windows ................................................... 12**2

Versions .............................................................. 12**3

Functions ............................................................. 12**4

Error Codes ........................................................... 12**5

CHAPTER 13 Network APIs

FTP Driver - PC/TCP Packet Driver Specification ....................... 13**1

10-Net Network ........................................................ 13**2

LANtastic LANOS API ................................................... 13**3

Novell NetWare 2.11 API ............................................... 13**4

APPC/PC ............................................................... 13**5

CHAPTER 14 Mouse Programming

General Information ................................................... 14**1

Interrupt 33h Function Requests ....................................... 14**3

Interrupt 10h Function Requests ....................................... 14**4

CHAPTER 15 Register-Level Programming

8555 Peripheral Interface ............................................. 15**1

8259 Interrupt Controller ............................................. 15**2

AT CMOS RAM Configuration ............................................. 15**3

CHAPTER 16 Video Programming

Quick List of BIOS Interrupt 10h Functions ............................ 16**1

BIOS Interrupt 10h Functions in Detail ................................ 16**2

CHAPTER 17 Multitasking Shells

Introduction .......................................................... 17**1

Programming Practices ................................................. 17**2

TopView/DesQview API (interrupt 15h, "System Services" interface) ..... 17**3

TopView/DesQview API (interrupt 16h, "BIOS Video" interface) .......... 17**4

CHAPTER 18 Viruses and Trojan Horses

MISCSTUF Miscellaneous Stuff

AFTERWRD Afterword

A P P E N D I C E S

APPENDIX 1 Keyboard scan code chart

APPENDIX 2 ASCII character chart

APPENDIX 3 IBM PC character set

APPENDIX 4 IBM PC error code listing

APPENDIX 5 Addresses of various manufacturers

| grouped by product - monitors, keyboards, etc.

APPENDIX 6 Hard disk information

| formatting information for hundreds of hard disks

APPENDIX 7 Floppy and Tape Devices

APPENDIX 8 Pinouts of various connectors on the IBM PC

| need the pinout for an external floppy for your laptop?

| For a parallel loopback tester? An IBM printer cable?

| All these and more

APPENDIX 9 Sizes of various drivers installed in CONFIG.SYS

APPENDIX 10 Common modem instruction sets

APPENDIX 11 Glossary of computer terminology

APPENDIX 12 Various busses used in MSDOS machines

APPENDIX 13 Common filename extensions

APPENDIX 14 Clock speeds of various expansion cards

APPENDIX 15 Header formats used by various archive utilities

APPENDIX 16 Miscellaneous Hardware Information

APPENDIX 17 HP LaserJet Setup Codes

APPENDIX 18 ANSI.SYS

APPENDIX 19 DEC VT100 Escape Sequences

APPENDIX 20 Various Paint Program Formats

APPENDIX 21 Some Commonly Used Hot-Keys

APPENDIX 22 Sound Blaster API

APPENDIX 23 French-Canadian accented character chart

** Programmer's Technical Reference for MSDOS and the IBM PC **

ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿

³ Shareware Version, 06/17/91 ³

³ Please Register Your Copy ³

ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

ISBN 1-878830-02-3 (disk-based text)

Additional Readings...

I don't have and haven't seen most of this stuff, but I've come across

mentions of it. This list is purely FYI...

IBM's literature guide lists the following manuals:

Hardware Technical References:

PS/2 Model 25 $31.50 75X1055

PS/2 Model 30 $82.50 68X2201

PS/2 Model 30/286 $26.75 01F0237

PC $33.00 6322507 (the original)

PC/AT $115.00 6280070

supplement for AT/339 $54.50 6280099 (enhanced 8mHz)

XT/286 $55.00 68X2210

XT and Portable $54.50 6280089

Convertible $82.50 6280648

PCjr $38.50 1502293 (availability varies)

PS/2 Hardware Interface $137.00 68X2330

(Micro Channel docs)

PS/2 BIOS Interface $137.00 68X2341 (no source code listing)

Advanced BIOS Interface $50 68X2288

DOS 3.3 Technical Ref. $93.00 6280059 (no reference for 4.0)

DOS 4.0 Command Ref. $31.50 6280253 (commands only)

8514/A Developer's Guide $26.75 68X2279

There is supposed to be a DOS 4.0 Technical Reference, but there's no name or

part number listed in the official IBM literature. You might check with your

local IBM retailer. (hah!)

DOS 4.0 Technical Ref. $--.-- 6280254 (not listed in catalog)

IBM NetBIOS Application

Development Guide (API) $49.25 68X2270 (not listed in catalog)

address:

IBM Technical Directory 800-426-7282

PO Box 2009 414-633-8108

Racine WI 53404-3336 BC, Canada 112-800-465-1234

Canada 800-465-1234

catalogs are free

Zenith Data Systems' "MS-DOS version 2 Programmer's Utility" comes with MASM,

a version of the MS-DOS Programmer's Reference from Microsoft, the assembly

language source for Zenith's ANSI.SYS driver, an editor, an assortment of

filters and utilities, and the source listing for the "device dependent"

portion of MS-DOS for the Z-151.

"Document Content Architecture: Revisable - Form - Text Reference"

IBM Document SC23-0758-1

IGES (International Graphics Exchange Specification) 3.0 documentation,

Global Engineering Documents (800) 854-7179. Part number NBSIR 86-3359, NBS.

ISBN 0-672-22027-X "Interfacing To the IBM Personal Computer" by

Lewis C. Eggebrecht, Howard W Sams & Co., Indianapolis, IN.

Intel Application Note AP-133, "Getting Started with the Numeric Data

Processor," by Bill Rash. February 1981.

Intel iAPX 286 Programmer's Reference Manual, including the iAPX 286

Numeric Supplement, Intel part no. 210498-003. Has some reasonably useful

example codes in section 4, including ASCII to binary and vice versa on

pages 4-7 to 4-14 and trig functions on 4-18 to 4-23. The programming

style in these examples is rather bizarre but they are better than nothing.

Intel 80387 Programmer's Reference Manual, Intel part no. 231917-001.

Various example listings on pages 7-7 to 7-17, including ASCII to binary

and binary to ASCII conversions and raising a number to a power. No trig

routines in this manual because the 80387 has built-in FSIN, FCOS, and FSINCOS

instructions and generalized FPTAN and FPATAN instructions that make

subroutines unnecessary.

Hercules sells a graphics library for the Herc board called GRAPHX for $50.

DoD Trusted Computer System Evaluation Criteria (popularly known as "The

Orange Book) GPO Stock No 008-000-00461-7 Cost $6.00

Information Interchange Standards:

ANSI X 3.15-1976 (FIPS 16-1)

Bit Sequencing In Serial-By-Bit Data Transmission.

ANSI X3.16-1976 (FIPS 17-1)

Character Structure and Parity-Sense, Serial-By-Bit.

ANSI X3.25-1976 (FIPS 18-1)

Character Structure and Parity-Sense, Parallel-By-Bit.

ANSI X3.4-1977 (FIPS 1-1)

Code for Information Interchange

ANSI X3.41-1974 (FIPS 35)

Code Extension Techniques for Use With 7-Bit Coded Characters.

ANSI X3.64-1979 (FIPS 86)

Additional Controls for Use With...

ANSI X3.32-1973 (FIPS 1)

Graphic Representation of the Control Characters.

ANSI X3.78-1981

Representation of Vertical Carriage positoning Characters.

ANSI X3.42-1975

Representation of numeric values in Character Strings.

ANSI X3.98-1983

Page Image Format (PIF), Text, for Information Systems.

ANSI X3.28-1976

Procedure for the Use of Communications Control Characters.

ANSI X3.66-1979 (FIPS 71)

Advanced Data Communications Control Procedures (ADCCP)

Data Encryption Standards:

ANSI-X3.92-1981

Data Encryption Algorithm

ANSI-X3.105-1983

Data Link Encryption

ANSI-X3.106-1983

Modes of Operation of Data Encryption Algorithm

Serial Interface Standards:

RS-232-C Aug 1969 (June 1981)

Interface Between Data Terminal Equipment (DTE) and

Data Communications Equipment (DCE)

Bulletin #9 May 1971 (Application Notes)

...reviews methods of operation...service and trans-

mission facility characteristics...

Bulletin #12 Nov 1977 (Application Notes)

Interconnection Between RS-449 and RS-232-C ...

Bulletin #14 Mar 1982 (Application Notes)

Loop Test Circuits Not Defined in RS-232-C

RS-336-A Mar 1979

Interface Between DTE and Automatic Calling Equipment

RS-449 Nov 1977

RS-449-1 Addendum 1 Feb 1980

General Purpose 37- and 9-Position Interface for DTE

and Data Circuit-Terminating Equipment (DCE)...

Standards Groups:

AFIP (Federal Information Processing Standards)

Office of Technical Information and Publications

National Bureau of Standards

Washington, D.C. 20234

ANSI American National Standards Institute, Inc.

1430 Broadway

New York, New York 10018

BELL ??

EIA Electronic Industries Association

2001 Eye Street

Washington, D.C. 20006

CCITT ??

ISO International Standards Organization

(available through ANSI)

Coding and Information Theory by Richard W. Hamming (Prentice-Hall, 1980)

Error Correcting Codes by W. Wesley Peterson (MIT Press and Wiley, 1961)

Handbook of Software & Hardware Interfacing for IBM PCs

Jefferey P. Royer

1987 by Prentice-Hall, Inc. (Osborne-McGraw-Hill)

Englewood Cliffs, NJ 07632

ISBN 0-13-381831-4 hardware and expansion card design and interfacing

The C Programmer's Guide to NetBios, W. David Schwaderer, Howard W Sams &

Company, ISBN 0-672-22638-3 $24.95.

Computer Networks - Andrew S. Tanenbaum,Prentice Hall, ISBN 0-13-162959-X

Local Area Networks - Thomas W.Madron - Wiley, ISBN 0-471-85989-3

Netware APIs: There are many API packages available from Novell. Some of them:

Value-Added Process API $10.00 part number 420-10361-001

Netware Enhancements Package (security APIs, Queue Management, Accounting

Services) $15.00 part number 420-010316-110

Peer to Peer Comm. $15.00 part # 421-10070-001

Message Handling Service Interface $15.00 part # 420-10360-001

Novell API Reference Manual vols 1 & 2 $25.00 each part #s 452-760041-001

and 452-760042-001

C language Novell API Reference $250.00 part # 452-760043-001

Programmer's Guide $49.00 part # 420-000089-001

NetWare Technical Journal, 650 South Clark, Chicago, IL 60605-9960, pub. four

times a year for $50.00/yr.

SCSI specification: $25 from the American National Standards Institute,

1430 Broadway, New York, NY 10018, (212) 642-4900.

SCSI-2 X3T9.2 committee working documents, CAM committee documents, and the

most current draft of the SCSI-2 specification are available for downloading

from the SCSI BBS at (316) 636-8700 (300, 1200, or 2400 bps; 24 hours).

A paper copy of the SCSI-2 draft specification is available for $60 from

Global Engineering Documents 2805 McGaw Ave., Irvine, CA 92714,

(800) 854-7179 or (714) 261-1455.

SMB protocol (used by Microsoft in MS-Net and Lan Manager) "IBM Personal

Computer Seminar Proceedings", Volume 2, Number 8-1, G320-9310-00.

Security (DES, etc): NCSC's VENDOR'S GUIDE (dark green book [part of the

Rainbow series of books]). Write to: National Security Agency, ATTN: S613,

Ft. George Meade, MD 20755-6000, or call (301) 688-6581.

Programmer's Guide to PC & PS/2 Video Systems

Richard Wilton

Microsoft Press 1987

ISBN 1-55615-103-9

Logitech Mouse Tech. Ref. and Programmer's Guide v2.0, $25 (415)795-0801

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