Note: This API calls are shared between DOS and Win16 personality.

DOSX is a specialized version of DPMI. Windows standard and extended mode kernel is a DPMI client app. Standard and extended mode kernel differs minimally and shares common codebase. Standard mode is just DPMI client, exnhanced mode is DPMI client running under Virtual Machime Manager. 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 provides Version 1.0 DPMI support, but reported as 0.9.

2021/08/05 12:15 · prokushev

Int 31H, AH=00H, AL=0CH




Set Descriptor


AX = 000CH
BX = selector
ES:(E)DI = selector:offset of 8-byte buffer containing descriptor


if function successful
Carry flag = clear

if function unsuccessful
Carry flag = set
AX = error code
8021H	invalid value (access rights/type byte invalid)
8022H	invalid selector
8025H	invalid linear address (descriptor references a linear address range outside that allowed for DPMI clients)


Copies the contents of an 8-byte buffer into the LDT descriptor for the specified selector.

32-bit programs must use ES:EDI to point to the buffer. 16-bit programs should use ES:DI.

The descriptor's access rights/type byte (byte 5) follows the same format and restrictions as the access rights/type parameter (in CL) for the Set Descriptor Access Rights function (Int 31H Function 0009H). On 80386 (or later) machines, the descriptor's extended access rights/type byte (byte 6) follows the same format and restrictions as the extended access rights/type parameter (in CH) for the same function, except the low-order 4 bits (marked “reserved”) are used to set the upper 4 bits of the descriptor's limit.

If the descriptor's present bit is not set, then the only error checking is that the client's CPL must be equal to the descriptor's DPL field and the “must be 1” bit in the descriptor's byte 5 must be set.

A DPMI 1.0 host will reload any segment register which contains a selector specified in register BX. It is suggested that DPMI 0.9 hosts also implement this.

Refer to the rules for descriptor usage in Appendix D.

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/int31/00/0c.txt · Last modified: 2021/08/27 03:46 by prokushev