0040h:0040h           Motor Off Counter

    Length: 1 byte

    Keeps count of the number of ticks (18.2 ticks per second) before
    the diskette motor is turned off. Int 08h decrements this count
    every time it is executed, if a motor is on. After this value
    reaches 0, the motor is turned off and the Diskette Motor Status
    byte (0040h:003Fh) is adjusted.