Editing DOS Protected Mode Interface (section)

== Overview ==
DPMI stands for DOS Protected Mode Interface.
It is an [[API]] that allows a program to run in [[protected mode]] on 80286 series and later processors, and do the
calls to [[real mode]] without having to set up these CPU modes manually. DPMI also provides the functions for managing
various resources, notably [[Computer Memory|memory]]. This allows the DPMI-enabled programs to work in
[[Computer_multitasking|multi-tasking]] OSes,
allowing an OS kernel to distribute such resources between multiple applications. DPMI provides only the functionality that
needs to be implemented in [[Protection_ring#SUPERVISOR-MODE|supervisor mode]]. It can be
thought of as a single-tasking [[microkernel]]. The rest of the functionality is available to DPMI-enabled programs
via the calls to real-mode [[DOS]] and [[BIOS]] services, allowing the DPMI API itself to remain mostly independent of DOS.
Things that make DPMI API DOS-specific, are just 3 functions for managing DOS memory, and the letter "D" in the "DPMI" acronym.

A DPMI service can be 16-bit, 32-bit, or "universal" and is called the ''DPMI kernel'', ''DPMI host'', or ''DPMI server''. It is provided either by the host operating system (''virtual DPMI host'') or by a [[DOS extender]] (''real DPMI host''). The DPMI kernel can be a part of a DOS extender such as in [[DOS/4GW]] or [[DOS/32A]], or separate, like [[CWSDPMI]] or [[HDPMI]].

The primary use of DPMI API is to allow [[DOS extender]]s to provide the host-OS-agnostic environment.
DOS extender checks the presence of a DPMI kernel, and installs its own only if the one was not installed already. This allows
DOS-extended programs to run either in a multitasking OS that provides its own DPMI kernel, or directly
under [[bare-metal]] DOS, in which case DOS extender uses its own DPMI kernel. Windows 3.x and 9x's [[user-mode]]
kernels are built with a DOS extender, so they fully rely on a DPMI API that is provided by Windows's ring-0 kernel.