Process management

To isolate your program from dependencies on PSP structure and relocation information, use the EXEC function (Int 21H Function 4BH) when loading overlays or other programs. Terminate your program with Int 21H Function 4CH, passing a zero return code if the program executes successfully and a nonzero code if an error is encountered. Your program's parent can then test this return code with Int 21H Function 4DH or, in a batch file, with the IF ERRORLEVEL statement.