Guide >> Concepts >> Understanding FAT File System

Understanding File System (FAT)

The file allocation table (FAT) file system is a simple file system originally designed for small disks and simple folder structures.  It is thusly named for its method of organization by storing entries in a table which resides at the beginning of the volume. The file allocation tables and the root folder must also 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

The next figure illustrates how the FAT file system organizes a volume.

See the next sections for more information about FAT:

• FAT Partition Boot Sector
• FAT File Allocation Table
• FAT Root Folder
• FAT Folder Structure
• FAT32 Features

Differences between FAT12, FAT16, FAT32

• a FAT12 file system contains 1.5 bytes per cluster within the file allocation table.
• a FAT16 file system contains 2 bytes per cluster within the file allocation table.
• a FAT32 file system includes 4 bytes per cluster within the file allocation table.

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