Online HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens
INT 21,4B - EXEC/Load and Execute Program
AH = 4B
AL = 00 to load and execute program
= 01 (Undocumented) create program segment prefix and load
program, but don't execute. The CS:IP and SS:SP of the
program is placed in parameter block. Used by debuggers
= 03 load program only
= 04 called by MSC spawn() when P_NOWAIT is specified
DS:DX = pointer to an ASCIIZ filename
ES:BX = pointer to a parameter block
on return:
AX = error code if CF set (see DOS ERROR CODES)
ES:BX = when AL=1, pointer to parameter block similar to:
Offset Size Description
00 word when AL=1, segment of env. or zero if using parents env.
word when AL=3, segment of load point for overlay
02 dword when AL=1, pointer to cmd line at PSP 80h
word when AL=3, relocation factor for EXE overlay
06 dword pointer to default FCB passed at PSP 5Ch
0A dword pointer to default FCB passes at PSP 6Ch
0E dword value of program SS:SP
12 dword value of program CS:IP
- allows execution of an external program as well as overlay
management from within an application
- all registers except CS and IP are destroyed
- SS and SP should be preserved in code segment before call
since a bug in DOS version 2.x destroys these
- return code can be retrieved if child process exits via INT 21,4C
- calling process must assure presence of enough unallocated memory
- subfunction 4 returns with an error under DOS 4.x+
- calls INT 21,55
- see also INT 21,26
[helppc.bosbyte.nl] exec function