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=00H, AL=06H
Get Segment Base Address
AX = 0006H BX = selector
if function successful Carry flag = clear CX:DX = 32-bit linear base address of segment if function unsuccessful Carry flag = set AX = error code 8022H invalid selector
Returns the 32-bit linear base address from the LDT descriptor for the specified segment.
Client programs must use the LSL instruction to query the limit for a descriptor. Note that on 80386 machines, the client must use the 32-bit form of LSL if the segment size is greater than 64 KB.
Refer to the rules for descriptor usage in Appendix D.
Text based on http://www.delorie.com/djgpp/doc/dpmi/