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=05H, AL=03H
Resize Memory Block
AX = 0503H BX:CX = new size of block (bytes, must be nonzero) SI:DI = memory block handle
if function successful Carry flag = clear BX:CX = new linear address of memory block SI:DI = new handle for memory block if function unsuccessful Carry flag = set AX = error code 8012H linear memory unavailable 8013H physical memory unavailable 8014H backing store unavailable 8016H handle unavailable 8021H invalid value (BX:CX = 0) 8023H invalid handle (in SI:DI)
Changes the size of a memory block that was previously allocated with either the Allocate Memory Block function (Int 31H Function 0501H) or the Allocate Linear Memory Block function (Int 31H Function 0504H).
After this function returns, the previous handle for the memory block is invalid and should not be used.
When increasing the size of a block, this function always creates committed pages. When decreasing the block size, this call will correctly free all possible page types (committed pages, uncommitted pages, and mapped pages). The linear address and handle of the memory block may change as a result of this call.
It is the client's responsibility to update any descriptors that map the memory block with the new linear address after resizing the block.
This function returns an error if the client attempts to resize a memory block to zero bytes.
Text based on http://www.delorie.com/djgpp/doc/dpmi/