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Note: This API calls are shared between DOS and Win16 personality.
DPMI is a shared interface for DOS applications to access Intel 80286+ CPUs services. DOS DMPI host provides core services for protected mode applications. Multitasking OS with DOS support also provides DMPI in most cases. Windows standard and extended mode kernel is a DPMI client app. Standard and extended mode kernel differs minimally and shares common codebase. Standard Windows kernel works under DOSX extender. DOSX is a specialized version of 16-bit DPMI Extender (but it is standard DPMI host). Standard mode is just DPMI client, exnhanced mode is DPMI client running under Virtual Machime Manager (really, multitasker which allow to run many DOS sessions). Both modes shares DPMI interface for kernel communication. The OS/2 virtual DOS Protected Mode Interface (VDPMI) device driver provides Version 0.9 DPMI support for virtual DOS machines. Win16 (up to Windows ME) provides Version 0.9 DPMI support.
DPMI host often merged with DPMI extender. Usually DPMI extender provide DPMI host standard services and DOS translation or True DPMI services.
Int 2FH, AH=16H, AL=8AH
Get Vendor-Specific API Entry Point
AX = 168AH DS:(E)SI = selector:offset of ASCIIZ (null-terminated) string identifying the DPMI host vendor
if function successful AL = 0 ES:(E)DI = extended API entry point and DS, FS, GS, EAX, EBX, ECX, EDX, ESI, and EBP are preserved.
if function unsuccessful AL = unchanged (8AH)
Returns an address which can be called to use host-specific extensions to the standard set of DPMI functions. This function is available only in protected mode.
The ASCIIZ string specifies a host vendor name or some other unique identifier to obtain a specific extension entry point. The string comparison used to look up the API entry point is case-sensitive.
Clients must use a FAR CALL to reach the extended API entry point.
All extended API parameters are specified by the vendor.
DPMI 1.0 clients should use this function in preference to Int 31H Function 0A00H. This method of API extension is preferable to the Int 31H extension as it avoids the creation of a long (and consequently slow) chain of Int 31H handlers which would slow down time-critical DPMI functions. Note that although this function was not documented for DPMI 0.9, it will work under any DPMI 0.9 host.
Text based on http://www.delorie.com/djgpp/doc/dpmi/