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 * * *