VCPI (Virtual Control Program Interface)

Specification for managing memory beyond the first megabyte on PCs with 80386 or later processors. VCPI can allocate memory to an application as either expanded or extended memory, as required by the application design. The VCPI standard is supported by some memory managers and DOS extenders.      The Intel 80386 microprocessor has three fundamental operating modes. Real mode is provided for backward compatibility with existing 8086 programs. Protected mode allows programs written specifically for the 80386 to take advantage of the larger address space available. Virtual 8086 (V86) mode, like real mode, is used to run 8086 programs. However, V86 mode runs under the control of a protected mode operating environment. This provides certain advantages, chiefly the ability to enable the paging hardware of the 80386 and thus run multiple 8086 programs simultaneously, and also the ability to make arbitrary physical memory available within the V86 address space of an 8086 program. (The 80486 microprocessor provides the same architecture and operating modes as the 80386, thus software written for the 80386 runs without modification on an 80486).      The capabilities of the 8086 have spawned the creation of several new kinds of control programs that can run under MS-DOS on a 386 machine. To date, these programs fall into three basic categories: (1) protected mode run-time environments, which allow an application program to execute in protected mode under MS-DOS; (2) EMS emulators, which use V86 mode to make all the memory on the machine available to 8086 programs which use EMS (Lotus/Intel/Microsoft Expanded Memory Specification) memory, and, (3) multitasking environments which use V86 mode to multitask 8086 MS-DOS programs, while still giving each 8086 program a full 640Kb of physical memory (or more, if they use EMS memory). Such multitasking environments typically run in conjunction with a separate EMS emulator, or implement the EMS interface as part of the multitasker. For the remainder of this specification, the terms "DOS- Extender," "EMS emulator," and "multitasker," respectively, will be used to refer to these program categories.      Since these control programs run under MS-DOS, it is desirable to make them compatible with each other, so that users don't have to turn off one control program in order to run an application under another control program. The purpose of this document is to specify an interface that allows these classes of control programs to coexist successfully. This interface is called the Virtual Control Program Interface, or VCPI.

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Last Update: 2:20 PM 11/8/01