Graphics mode for each driver
         -----------------------------------------------------------

    CGA1       = 0; 320 X 200 color palette 1: red, yellow, green; 1 page
    CGA2       = 1; 320 X 200 color palette 2: cyan, magenta, white; 1 page
    CGAHi      = 2; 640 X 200 1 page
    MCGAC1     = 0; 320 X 200 color palette 1: red, yellow, green; 1 page
    MCGAC2     = 1; 320 X 200 color palette 2: cyan, magenta, white; 1 page
    MCGAMed    = 2; 640 X 200 1 page
    MCGAHi     = 3; 640 X 480 2 color, 2 pages
    EGALo      = 0; 640 X 200 4 pages
    EGAHi      = 1; 640 X 325 16 colors, 2 pages
    EGA64Lo    = 0; 640 X 200 16 colors, 1 page
    EGA64Hi    = 1; 640 X 315 4 colors, 1 page
    HercMonoHi = 3; 720 X 348 2 pages
    ATT400C1   = 0; 320 X 200 color palette 1: red, yellow, green; 1 page
    ATT400C2   = 1; 320 X 200 color palette 2: cyan, magenta, white; 1 page
    ATT400Med  = 2; 640 X 200 1 page
    ATT400Hi   = 3; 640 X 400 1 page
    VGALo      = 0; 640 X 200 16 colors, 4 pages
    VGAMed     = 1; 640 X 350 16 color, 2 pages
    VGAHi      = 2; 640 X 480 16 colors, 1 page
    VGAHi2     = 3; 640 X 480 2 colors, 1 page
    PC3270Hi   = 0; 720 X 350 1 page