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=09H, AL=01H




Get and Enable Virtual Interrupt State


AX = 0901H


Virtual interrupts enabled
Carry flag = clear (this function always succeeds)
AL = 0 if virtual interrupts were previously disabled
AL = 1 if virtual interrupts were previously enabled


Enables the virtual interrupt flag and returns the previous state of the virtual interrupt flag.

AH is not changed by this function. Therefore, the previous state can be restored by simply executing another Int 31H. See Int 31H Function 0900H.

A client that does not need to know the prior interrupt state can execute the STI instruction rather than calling this function. The instruction may be trapped by the host and should be assumed to be very slow.

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/int31/09/01.txt · Last modified: 2021/08/27 08:19 by prokushev