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.

2021/08/05 12:15 · prokushev

Int 31H, AH=01H, AL=01H




Free DOS Memory Block


AX = 0101H
DX = selector of block to be freed


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


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All descriptors allocated for the memory block are automatically freed by this function, and are no longer valid after this function returns.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


Process manager INT 2FH 1680H, 1687H
Memory manager
Misc INT 2FH 1686H, 168AH
2021/08/13 16:23 · prokushev

en/docs/dpmi/api/int31/01/01.txt · Last modified: 2021/08/27 04:03 by prokushev