In computing, the Virtual Control Program Interface (VCPI) is a specification published in 1989 by Phar Lap Software that allows a DOS program to run in

protected mode In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as Memory_segmentation, segmentation, virtual mem ...

, granting access to many features of the processor not available in

real mode Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20- bit s ...

. It was supplanted by

DOS Protected Mode Interface In computing, the DOS Protected Mode Interface (DPMI) is a specification introduced in 1989 which allows a DOS program to run in protected mode, giving access to many features of the new PC processors of the time not available in real mode. It w ...

(DPMI) shortly after being introduced, due in large part to VCPI's inability to work in Windows 3.0's protected mode.

Overview

Developed since 1987 in cooperation with Quarterdeck Office Systems and with support by A.I. Architects, Lotus Development Corp., Quadram, Qualitas and Rational Systems, VCPI is provided by an

expanded memory In DOS memory management, expanded memory is a system of bank switching that provided additional memory to DOS programs beyond the limit of conventional memory (640 KiB). ''Expanded memory'' is an umbrella term for several incompatible tech ...

manager in DOS (e.g. CEMM, QEMM, later

EMM386 EMM386 is the expanded memory manager of Microsoft's MS-DOS, IBM's PC DOS, Digital Research's DR-DOS, and Datalight's ROM-DOS which is used to create expanded memory using extended memory on Intel 80386 CPUs. There also is an EMM386.EXE avail ...

) and does allow 80386 protected-mode DOS extenders to coexist with 80386 EMS expanded memory emulators. It was eclipsed by DPMI, most notably because it was not supported for DOS programs run in Windows 3.0's native

(called ''386 enhanced mode'') and because VCPI runs programs in

Ring (The) Ring(s) may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell Arts, entertainment, and media Film and TV * ''The Ring'' (franchise), a ...

0, which defeated the purpose of x86 protection. It also did not work with

OS/2 OS/2 is a Proprietary software, proprietary computer operating system for x86 and PowerPC based personal computers. It was created and initially developed jointly by IBM and Microsoft, under the leadership of IBM software designer Ed Iacobucci, ...

2.0 and later. VCPI was only supported in Windows 3.0 real mode, some programs could run in Windows 3.x standard mode. Standard mode (286 mode) Windows 3.1 (but not 3.0) itself was VCPI compliant (it was a VCPI client). Earlier Windows/386 2.1 was not compatible with DOS extenders at all.

Windows NT Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...

DOS box did not support VCPI either. VCPI also had a comparatively limited scope in that it allowed a protected mode DOS program to run only when the program was started from DOS already running inside a

virtual 8086 mode In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running ...

task. (This was typically accomplished through a memory manager operating as a ''virtual

ode An ode (from ) is a type of lyric poetry, with its origins in Ancient Greece. Odes are elaborately structured poems praising or glorifying an event or individual, describing nature intellectually as well as emotionally. A classic ode is structu ...

control program'' for the processor.) Because the virtual 8086 mode isolates programs from the hardware, it is not possible for a program to switch to protected mode without some support from the control program.

Extended VCPI

Between 1989 and February 1990 an alternative specification was proposed under the name Extended VCPI (XVCPI) by a number of companies including Intel's Software Focus Group, Lotus,

Digital Research Digital Research, Inc. (DR or DRI) was a privately held American software company created by Gary Kildall to market and develop his CP/M operating system and related 8-bit, 16-bit and 32-bit systems like MP/M, Concurrent DOS, FlexOS, Multiuser ...

Interactive Systems Interactive Systems Corporation (styled INTERACTIVE Systems Corporation, abbreviated ISC) was a US-based software company and the first vendor of the Unix operating system outside AT&T, operating from Santa Monica, California. It was founded in 19 ...

, Viewport International and others to address some of the shortcomings of VCPI and better exploit the memory management and multitasking capabilities of the 386 processor. It was used by a small number of products including operating systems like

Interactive Unix Interactive Systems Corporation (styled INTERACTIVE Systems Corporation, abbreviated ISC) was a US-based software company and the first vendor of the Unix operating system outside AT&T, operating from Santa Monica, California. It was founded in 19 ...

and Concurrent DOS 386. Since February 1990 these efforts ultimately succumbed to the (parallel) development and publication of the DPMI specification in May 1990, which addressed similar problems, but was compatible with the implementation of Microsoft Windows 3.0 to be released the same year. In February 1991, the

Multiuser DOS Federation The Multiuser DOS Federation (MDOS) was an industry alliance to promote the growth and acceptance of multi-user DOS-based solutions on 286, 386 and 486 computers. It was formed in July 1990. Initially among them were Digital Research, Theos S ...

(MDOS), an initiative formed in July 1990, issued a statement regarding their support of DPMI.

Overview

Extended VCPI

See also

Notes

References

Further reading