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=06H, AL=03H
Relock Real Mode Region
AX = 0603H BX:CX = starting linear address of memory to relock SI:DI = size of region to relock (bytes)
if function successful Carry flag = clear if function unsuccessful Carry flag = set AX = error code 8002H invalid state (region not marked as pageable) 8013H physical memory unavailable 8025H invalid linear address (region is above 1 MB boundary)
Relocks a memory region that was previously declared as pageable with the Mark Real Mode Region as Pageable function (Int 31H Function 0602H).
If the function returns an error, none of the memory has been relocked.
If the specified region overlaps part of a page at the beginning or end of the region, the page(s) will not be relocked.
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.
If Function 0602H is implemented as a “no-operation” on a particular DPMI host, this function will likewise do nothing. In other words, this function should not be used to lock memory, but only to restore the default state of the host's conventional memory locking.
Text based on http://www.delorie.com/djgpp/doc/dpmi/