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Understanding File System (FAT)
The FAT file system is a simple file system originally designed for
small disks and simple folder structures. The FAT file system is named for its
method of organization, the file allocation table, which resides at the
beginning of the volume. To protect the volume, two copies of the table are
kept, in case one becomes damaged. In addition, the file allocation tables and
the root folder must be stored in a fixed location so that the files needed to
start the system can be correctly located.
A volume formatted with the FAT file system is allocated in clusters.
The default cluster size is determined by the size of the volume.
For the FAT file system, the cluster number must fit in 16 bits and must be a power of two.
Structure of a FAT Volume
Next figure illustrates how the FAT file system organizes a volume.
See the next sections for more information about FAT:
Differences between FAT12, FAT16, FAT32
- FAT12 file system contains 1.5 bytes per
cluster within the file allocation table.
- FAT16 file system contains 2
bytes per cluster within the file allocation table.
- FAT32 file system includes 4 bytes per cluster within the file
allocation table.
System |
Cluster limit |
FAT12 |
The count of data clusters is less than 4087 clusters.
|
FAT16 |
The count of data clusters is between 4087 and 65526 clusters,
inclusive. |
FAT32 |
The count of data clusters is between 65526 and 268,435,456
clusters, inclusive. |
For more detailed information see resource kits on Microsoft's web site
http://www.microsoft.com/windows/reskits/webresources/default.asp
or Microsoft Developers Network (MSDN) http://msdn.microsoft.com
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