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=0DH, AL=01H




Free Shared Memory


AX = 0D01H
SI:DI = handle of shared memory block to free


if function successful
Carry flag = clear

if function unsuccessful
Carry flag = set
AX = error code
8023H	invalid handle


Deallocates a shared memory block.

The shared memory handle becomes invalid after the shared memory block is deallocated, and should not be used in any other function call (such as serialization).

The host maintains virtual machine use counts and a global use count for each shared memory block. A virtual machine use count is the number of allocation calls (Int 31H Function 0D00H) that have been issued by a particular virtual machine for the shared block, while the global use count corresponds to the number of virtual machines which have access to the block. When a virtual machine use count reaches zero, the clients in that virtual machine no longer have addressability to the shared memory block; when the global use count reaches zero, the shared memory block is destroyed by the host.

It is the client's responsibility to free any descriptors that it has allocated to map the shared memory block.

Applications should not depend on this function to release a previous successful serialization for the same shared memory block. Serialization is only released by this function when the virtual machine use count goes to 0 (i.e., the client no longer has access to the shared memory block).

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/int31/0d/01.txt · Last modified: 2021/08/27 08:42 by prokushev