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 31H, AH=09H, AL=00H
Get and Disable Virtual Interrupt State
AX = 0900H
Virtual interrupts disabled Carry flag = clear (this function always succeeds) AL = 0 if virtual interrupts were previously disabled AL = 1 if virtual interrupts were previously enabled
Disables 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 0901H.
A client that does not need to know the prior interrupt state can execute the CLI instruction rather than calling this function. The instruction may be trapped by the host and should be assumed to be very slow.
Text based on http://www.delorie.com/djgpp/doc/dpmi/