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Int 10h, 12h /BL=32h    Select Video Addressing                     MCGA, VGA

    Enables or disables CPU access to video RAM and the video
    adapter's I/O registers.

        Entry   AH = 12h
                AL = 0 | 1   Enable | disable access
                BL = 32h

        Return  AL = 12h   If function supported


    If more than one display device is residing in the system with the
    same host port addresses or host memory addresses, this service
    allows one device to be effectively pulled out of the system to
    avoid bus conflicts.

    Disabling the video can improve the data transfer speed when data
    is sent from the host to the VGA since the video refresh logic is
    not competing for the memory bus.