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The media descriptor indicates the type of medium currently in a drive. With MS-DOS and Windows 95, you do not have to set the media descriptor byte. Therefore this problem does not occur with these older operating systems.
The media descriptor byte is located in the BPB of the boot sector at offset 21 (15h) and in the first byte of each FAT on the disk.
To work around this problem, use a disk sector editor to change the BPB media descriptor byte to the appropriate value. For example, you can use the DiskProbe tool to do this on a Windows NT 4.0-based, Windows 2000-based, Windows XP-based, or Windows Server 2003-based computer. DiskProbe (Dskprobe.exe) is included with the Windows Support Tools for Windows XP Professional and Windows XP 64-Bit Edition, the Windows 2000 Support Tools, and Windows NT 4.0 Resource Kit Support Tools.
The following table lists the most common media descriptor bytes:
The BPB media descriptor byte is located in sector 0 of the disk, and looks similar to this:
Byte Capacity Media Size and Type
F0 2.88 MB 3.5-inch, 2-sided, 36-sector
F0 1.44 MB 3.5-inch, 2-sided, 18-sector
F9 720K 3.5-inch, 2-sided, 9-sector
F9 1.2 MB 5.25-inch, 2-sided, 15-sector
FD 360K 5.25-inch, 2-sided, 9-sector
FF 320K 5.25-inch, 2-sided, 8-sector
FC 180K 5.25-inch, 1-sided, 9-sector
FE 160K 5.25-inch, 1-sided, 8-sector
FE 250K 8-inch, 1-sided, single-density
FD 500K 8-inch, 2-sided, single-density
FE 1.2 MB 8-inch, 2-sided, double-density
F8 ----- Hard disk
0000 EB 3C 90 4D 53 44 4F 53 35 2E 30 00 02 01 01 00
0010 02 E0 00 40 0B F0 09 00 12 00 02 00 00 00 00 00
xx <---- This byte above XX is the media descriptor
byte and is at offset hexadecimal 21 (15h).