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=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.

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/int31/05/03.txt · Last modified: 2021/08/27 06:18 by prokushev