Understanding FAT

[9691 Discussion Group]

Understanding FAT
FAT stands for File Allocation Table, but is also used as a name for
the family of file systems that have been used in DOS and Windows 9x
and supported by NT and various *NIX. An understanding of this file
system is required for data recovery and to understand ScanDisk's
reporting; fortunately, this is fairly easy to do. Armed with this
understanding, you can troubleshoot file system problems, even those
involving the FAT itself.

Terminology
This can be quite confusing, so I'll clarify this at the start:

FAT: File Allocation Table, a data structure present in all FAT
volumes
FAT1: The first copy of the FAT
FAT2: The first copy of the FAT
FAT12: FAT file system using 12-bit cluster addressing
FAT16: FAT file system using 16-bit cluster addressing
FAT32: FAT file system using 32-bit cluster addressing; Win95 SR2 and
later
FAT or FATxx: File systems that use File Allocation Tables, etc.
VFAT: The 32-bit code used to operate the file system in Win9x GUI
mode
Cluster: Single unit of data storage at the FATxx file system logic
level
Sector: Single unit of storage at the physical disk level
Physical sector address: Sector address in absolute physical hardware
terms
CHS sector address: As above, expressed in Cylinder, Head, Sector
terms
Logical sector address: Sector address relative to the FATxx volume
Folder: A collection of named items as seen via Windows Explorer
File Folder: Modern Windows-speak for "directory"
Directory: A file system data structure that lists files and/or
directories
Directory entry: Points to a file or directory, and contains info
about it
Attributes: A collection of bits in a directory entry that describes it