INT 21 U - OS/2 v2.1+ Virtual DOS MachineA special type of virtual machine provided by OS/2 version 2.0, in which a copy of MS-DOS or an MS-DOS compatible operating system (or even an incompatible 8086 operating system) is run and appears to have full control of the system. See also Virtual Machine, INT 21h Function 64h. - GET WinOS2 CALL GATE ADDRESS AH = 64h DX = 0007h (function number) CX = 636Ch (magic value, "cl") BX = 0000h (indicates special request) Return: AX = call gate address Notes: if CX is not 636Ch on entry, INT 21/AH=6Ch is invoked, because a bug in OS/2 1.x FAPI erroneously called AH=64h instead of AH=6Ch used by WinOS2 to make direct calls to OS2KRNL, bypassing the overhead of DOSKRNL