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.

2021/08/05 12:15 · prokushev

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




Set Debug Watchpoint


AX = 0B00H
BX:CX = linear address of watchpoint
DL = size of watchpoint (1, 2, or 4 bytes)
DH = type of watchpoint
Value Breakpoint Type
0 execute
1 write
2 read/write


if function successful
Carry flag = clear
BX = watchpoint handle

if function unsuccessful
Carry flag = set
AX = error code
8016H	too many breakpoints
8021H	invalid value (in DL or DH)
8025H	invalid linear address (linear address not mapped or alignment error)


Sets a debug watchpoint at the specified linear address.

Under DPMI 1.0, the handle will be in the range 0-14. Under DPMI 0.9, the handle range is not limited.

The watchpoint handle corresponds to the bit number in the Virtual DR6 returned in the exception frame (see Int 31H Function 0212H and page 18 of the DPMI spec).

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/int31/0b/00.txt · Last modified: 2021/08/27 08:25 by prokushev