This is part of Win16 API which allow to create versions of program from one source code to run under OS/2 and Win16. Under OS/2 program can be running under Win-OS/2 if program is Windows NE executable, and with help on Windows Libraries for OS/2, if it is OS/2 NE executable. Here is a WLO to OS/2 API mapping draft
Call DOS API dispatcher
void Dos3Call(void);
Depends on function. Passed in registers.
Depends on function. Returns in registers.
This function invoke DOS API dispatcher. It has not any parameters or return codes defined. Parameters and return codes same as in corresponding DOS API. This call actually does int 21h to call dispatcher. NoHookDosCall can be used to call dispatcher directrly, not via int 21h
_asm mov ah, 02h Dos3Call();