Media Descriptor

 DOS defines a 1-byte code that (sometimes) can be used to identify the
 type of media that is being used by a disk device.  The Media Descriptor
 (also called the FAT ID byte) will be seen:

 ■ as a value obtained from DOS Fns 1bH, 1cH, and 32H
 ■ as the first byte of the FAT (DOS logical sector 1)
 ■ at offset 0aH of a BPBRec
 ■ at offset 15H of a BootSectorRec (in DOS logical sector 0)
 ■ in the data block used by DOS Fn 440dH (Generic IOCTL)

 Value  Media Types Defined as of DOS 5.0
 ▀▀▀▀▀  ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
  f0H   3½" (1.44 MB) 2 sides, 18 sectors
        3½" (2.88 MB  2 sides, 36 sectors
        5¼" (1.2 MB)  2 sides, 15 sectors
        (also used for other media types)

  f8H   fixed disk, any capacity

  f9H   3½" (720K)    2 sides,  9 sectors, 80 tracks
        5¼" (1.2 MB)  2 sides, 15 sectors, 80 tracks
  faH   5¼" (320K)    1 side,   8 sectors, 80 tracks
  fbH   3½" (640K)    2 sides,  8 sectors, 80 tracks

  fcH   5¼" (180K)    1 side,   9 sectors, 40 tracks
  fdH   5¼" (360K)    2 sides,  9 sectors, 40 tracks; also used on 8" disks
  feH   5¼" (160K)    1 side,   8 sectors, 40 tracks; also used on 8" disks
  ffH   5¼" (320K)    2 sides,  8 sectors, 40 tracks

 The media descriptor byte is not a particularly reliable way to ascertain
 media type.  Refer to other fields of the BPBRec or BootSectorRec to
 obtain track, sector, and head information.

 For instance, the boot sector of a RAM disk may show it to be a hard disk
 (f8H) or even some other value.

See Also: fn 1bH and fn 1cH (get FAT info)
          fn 32H (get drive parameter block)
          Device Drivers  (see DvRq 01H and DvRq 02H)