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.
Int 31H, AH=03H, AL=04H
Free Real Mode Callback Address
AX = 0304H CX:DX = real mode callback address to be freed
if function successful Carry flag = clear if function unsuccessful Carry flag = set AX = error code 8024H invalid callback address
Releases a real mode callback address that was previously allocated with the Allocate Real Mode Callback Address function (Int 31H Function 0303H).
Real mode callbacks are a limited system resource. A client should release any callback that it is no longer using.
Text based on http://www.delorie.com/djgpp/doc/dpmi/