AX = 1F on return: AX = 001F if successful FFFF if error ES:BX = previous INT 33 vector - restores vectors for INT 10 and INT 71 (8088/86) or INT 74 (286+) - INT 33 interrupt vector (software) is not affected - use of the vector returned in ES:BX to restore the previous INT 33 vector can cause problems since it contains the value of INT 33 before the driver was installed; any other hooks into INT 33 set after driver installation will not receive service