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=0DH
Version
0.9
Brief
Allocate Specific LDT Descriptor
Input
AX = 000DH BX = selector
Return
if function successful Carry flag = clear and descriptor has been allocated if function unsuccessful Carry flag = set AX = error code 8011H descriptor unavailable (descriptor is in use) 8022H invalid selector (references GDT or beyond the LDT limit)
Notes
The first 10H (16) descriptors (selector values 04H-7CH) are reserved for this function and must not be used by the DPMI host.
Under DPMI 0.9 hosts, if another application has already been loaded, some of descriptors reserved for allocation by this function may be already in use and unavailable. Under DPMI 1.0 hosts, each client has its own LDT and thus will have the full 16 descriptors available for use with this function.
Resident service providers (protected-mode TSRs) should not use this function.
Refer to the rules for descriptor usage in Appendix D.
See also
Note
Text based on http://www.delorie.com/djgpp/doc/dpmi/