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=06H, AL=01H
Version
0.9
Brief
Unlock Linear Region
Input
AX = 0601H BX:CX = starting linear address of memory to unlock SI:DI = size of region to unlock (bytes)
Return
if function successful Carry flag = clear if function unsuccessful Carry flag = set AX = error code 8002H invalid state (page not locked) 8025H invalid linear address (unallocated pages)
Notes
Unlocks a linear address range that was previously locked using the Lock Linear Region function (Int 31H Function 0600H).
If the function returns an error, none of the memory has been unlocked.
If the specified region overlaps part of a page at the beginning or end of the region, the page(s) will be unlocked.
A lock count is maintained for each locked page; the page is not unlocked until the lock count is decremented to zero (i.e. the number of Lock Region Int 31H Function 0600H calls has been balanced by the same number of Unlock Region Int 31H Function 0601H calls).
This function is ignored by DPMI implementations that do not support virtual memory; the function will return the Carry flag clear to indicate success, but has no other effect. DPMI hosts which support virtual memory may also choose to ignore this function, but such hosts must be able to handle page faults transparently at arbitrary points during a client's execution, including within interrupt and exception handlers.
See also
Note
Text based on http://www.delorie.com/djgpp/doc/dpmi/