IBM Monochrome Display Adapter

        This display adapter has only one mode - 80x25 text mode
        (14 scan lines per char.). It is also supported by the
        Hercules Graphics Board.

        The board is designed around the Motorola 6845 CRT
        controller module. There are 4K bytes of static memory on
        the adapter which is used for the display buffer. This buffer
        has two ports and may be accessed directly by the processor.
        The 4K memory is mapped in system memory as address B0000h
        through B1000h.