4b00H load and execute program                26H Build PSP     superseded 
4b01H load program
4b03H load overlay
4b05H set execution state (SetVer version info)

4dH get exit code of child process

31H terminate and keep memory (TSR)           INT 27H           superseded 
51H get PSP of current process      See also: TSR/Popup Functions
50H set current PSP                           Program Segment Prefix
34H get InDOS and ErrorMode addresses

INT 23H Ctrl+Break handler vector (default handler terminates program)
INT 24H Critical Error handler vector (default handler may terminate you)
INT 2fH aexxH Control execution of DOS commands

Program Startup & Exit  conditions when a program starts

Process Control Functions