Int 10h, 1A01h          Set Display Combination Code                MCGA, VGA

    Informs BIOS of the type of display connected to the computer.

        Entry   AX = 1A01h
                BL = Active display code    (see function 1A00h
                BH = Inactive display code   for list of codes)

        Return  AL = 1Ah   If function supported

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    Note
    This service sets BIOS's only indication of the type of display in
    use and should be used only by systems software.