VC VCPI DOS Extenders

 ID:VC VCPI DOS Extenders

Quarterdeck Technical Note #103

by Daniel Travison


  The VCPI, Virtual Control Program Interface, specification was

developed to allow multiple protected mode control programs to

coexist and interact within a single 80386(486) system.  The

specification consists of two parts - a VCPI server and several

VCPI clients.  The VCPI clients request memory and mode switching

services from the VCPI server.


  In a DESQview 386 system, the VCPI server is implemented within

QEMM-386 while the DOS Extended applications become VCPI clients. 

When the DOS Extended application requires memory services it

calls upon the VCPI server to perform them.  When QEMM-386 is not

present, the DOS Extender performs the services for itself.


  The end result is that DESQview is able to run a mix of real

mode and DOS Extended (protected mode) applications concurrently

on an 80386/486.


  80286 systems may run multiple 286 DOS Extended applications

only if the DOS Extenders utilize XMS services.  286 DOS Extended

applications may also be run with QEMM-386 as the VCPI Server on

80386/486 systems.


  There are several DOS Extenders on the market.  The following

is a list of the companies that I am aware of that produce DOS

Extenders.  There may be other companies currently, or are

planning to ship DOS Extender tools.


Company            286 DOS Extenders         386 DOS Extenders

Name            (16-bit protected mode)   (32-bit protected mode)


Ergo Computing, Inc.    OS286                      OS386

One Intercontinental Way

Peabody, MA 01960

Corp: 508 535-7510

Sales: 800 633-1925

Fax: 508 535-7512


Phar Lap                                      386 DOS Extender 60

Aberdeen Avenue

Cambridge, MA 02138

617-661-1510


Rational Systems, Inc.   D16M

220 North Main Street

Natick, MA 01760

508-653-6006


Phar Lap Notes:


  The A20 must be enabled at all times.  Run the program inside

DESQview using XDV.COM or ensure that QEMM is ON.  An XMS driver

(QEXT.SYS or HIMEM.SYS) or VDISK will accomplish the same

purpose.


       Copyright (C) 1991 by Quarterdeck Office Systems

              * * * E N D  O F  F I L E * * * 

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