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. Windows in Standard Mode provides DPMI services only for Windows Applications, not DOS sessions.
DPMI host often merged with DPMI extender. Usually DPMI extender provide DPMI host standard services and DOS translation or True DPMI services.
Int 31H, AH=01H, AL=01H
Version
0.9
Brief
Free DOS Memory Block
Input
AX = 0101H
DX = selector of block to be freed
Return
if function successful Carry flag = clear if function unsuccessful Carry flag = set AX = error code 0007H memory control blocks damaged (also returned by DPMI 0.9 hosts). 0009H incorrect memory segment specified (also returned by DPMI 0.9 hosts). 8022H invalid selector
Notes
Frees a memory block that was previously allocated with the Allocate DOS Memory Block function (Int 31H Function 0100H).
All descriptors allocated for the memory block are automatically freed by this function, and are no longer valid after this function returns.
Under DPMI 1.0 hosts, any segment registers which contain a selector being freed are zeroed by this function.
Refer to the rules for descriptor usage in Appendix D.
See also
Note
Text based on http://www.delorie.com/djgpp/doc/dpmi/