INT 15h,  42h (66)       Request System Power Off                 Convertible

    The system is powered off. The next time the system is turned on,
    control can be returned to the instruction following this power-off
    call. (PC Convertible only.)

       On entry:      AH         42h
                      AL         Event type code
                                 0 - Use Profile for Resume mode state
                                 1 - Resume mode no matter what

       Returns:       Carry      Set if error, else cleared
                      AH         Modified

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    Control is returned immediately if this service is not available. If
    it is available, then power is turned off. The next time the system is
    turned on, if the event type code (AL) is 1 or the System Profile (see
    Service 40h) has warm start mode set, the machine will start right
    where it left off, executing the program that generated this service.

       Notes:         This service is available only for the PC
                      Convertible.

                      Before the system is powered down, the diskette
                      motors are turned off.