INT 10 - FRIEZE v7.41+ - INSTALLATION CHECK
        AH = 0Fh
        SI = F123h
        DI = 321Fh
Return: AH = number of character columns
        AL = display mode (see AH=00h)
        BH = active page (see AH=05h)
        SI = DI = F345h if installed
Notes:  if mode was set with bit 7 set ("no blanking"), the returned mode will
          also have bit 7 set
        EGA, VGA, and UltraVision return either AL=03h (color) or AL=07h
          (monochrome) in all extended-row text modes
SeeAlso: AH=4Bh"FRIEZE"