BIOS Disk Drive Installed Data (Columbia PCs only) [0040:0069]
      (not valid on most clone computers)
  Bits Description
  ---- ------------------------------------------------
  0    0  8 inch external floppy drives
       1  5-1/4 external floppy drives
  1-3  highest drive address which Int 13 will accept
       (since the floppy drives are assigned 0-3, subtract 3
       to obtain the number of hard disks installed)
  4,5  # of hard disks connected to expansion controller
  6,7  # of hard disks on motherboard controller
       (if bit 6 or 7 = 1, no A: floppy is present and
       the maximum number of floppies from Int 11 is 3)