Function 20h    PRINT.COM  (DOS internal)        (AT, XT-286, PS/2 50+) 
entry   AH      20h 
	AL      subfunction 
		00h     unknown (PRINT) 
		01h     unknown (PRINT) 
		10h     sets up SysReq routine on AT, XT/286, PS/2 
		11h     completion of SysReq routine (software only) 
note 1) AL=0 or 1 sets or resets some flags which affect what PRINT does when 
	it tries to access the disk