File Allocation Table

File Allocation Table (FAT) is the underlying file system of DOS and Windows. The FAT file system comprises a File Allocation Table and a backup FAT.

In other words, the FAT file system acts like a table of contents for the directories and files of a partition of a hard disk drive.

FAT file systems start with a root directory that can contain a maximum allowable count of entries. Operating systems that use the FAT file system represent the root directory visually using a backslash '\' character. The root directory must exist at a specified location upon an active primary partition.

Each file is made up of one or many file allocation units called clusters. Each cluster is a fixed size. FAT supports a maximum of 65,525 clusters.

FAT supports hard disk drive with sizes not exceeding 2.0 gigabytes. FAT uses 16-bit file allocation table entries.

There are three types of FAT file system, 12-bit (FAT12), 16-bit (FAT) and 32-bit (FAT32). FAT refers specifically to 16-bit FAT.

FAT32

FAT32 is the file system of Microsoft Windows 95 OEM service release 2, Windows 98, Windows 2000, Windows XP.

It uses 32-bit file allocation table entries and the cluster size is usually 4096 bytes, but it can be anywhere from 512 bytes to 64 kbytes. The clusters specify the smallest amount of space that can be allocated to a file and consist of a fixed number of sectors.

VFAT

Microsoft introduced the VFAT system which is the FAT filesystem expanded to allow much longer filenames. There was a limit to the length for file names within the original FAT file system. That length could not exceed eight characters, a dot, followed by three additional characters referred to as a file name extension.