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=00H, AL=00H
Version
0.9
Brief
Allocate LDT Descriptors
Input
AX = 0000H CX = number of descriptors to allocate
Return
if function successful Carry flag = clear AX = base selector if function unsuccessful Carry flag = set AX = error code 8011H descriptor unavailable
Notes
Allocates one or more descriptors in the task's Local Descriptor Table (LDT). The descriptor(s) allocated must be initialized by the application with other function calls.
If more than one descriptor was requested, the function returns a base selector referencing the first of a contiguous array of descriptors. The selector values for subsequent descriptors in the array can be calculated by adding the value returned by Int 31H Function 0003H.
The allocated descriptor(s) will be set to “data” with the present bit set and a base and limit of zero. The privilege level of the descriptor(s) will match the application's code segment privilege level.
Refer to the rules for descriptor usage in Appendix D.
See also
Note
Text based on http://www.delorie.com/djgpp/doc/dpmi/