Interrupt 21h
Function  4Ch   Terminate a Process (EXIT) 
		Quit with ERRORLEVEL exit code  
entry   AH      4Ch 
	AL      exit code in AL when called, if any, is passed to next process 
return  none 
note 1) Control passes to DOS or calling program 
     2) return code from AL can be retrieved by ERRORLEVEL or function 4Dh 
     3) all files opened by this process are closed, buffers are flushed, and  
	the disk directory is updated 
     4) Restores Terminate vector from PSP:000Ah 
		 Ctrl-C vector from PSP:000Eh
		 Critical Error vector from PSP:0012h