First developed for use on floppy disks in 1977, the File Allocation Table, or FAT file system, has seen many variations throughout the years. Most modern Windows users would likely be familiar with FAT32, ExFAT, and maybe even FAT16, but there are some other variations. Although it was once the default file system in the Windows operating system (OS), it's since been phased out in favor of New Technology File System, or NTFS.

FAT
The original inception of FAT was an 8-bit system meant for floppy disks, and it remains the default for some flash memory cards, USB drives, and more. However, the 8-bit architecture limits the usefulness of the original FAT file system in modern computing.

FAT12
Only used for a few months in 1980, FAT12 was meant specifically for QDOS 0.10, which eventually became 86-DOS and the foundation for the MS-DOS and PC DOS operating systems in 1981. As the name implies, it provides enhanced functionality when compared to the 8-bit FAT system, but it still pales in comparison to the 16-bit FAT released years later.

FAT16
The first inception of FAT16 was introduced in 1984 for MS-DOS 3.0. Although the number of available cluster addresses was doubled from that of the original FAT, it kept the 32 MB max partition size. It's also important to note that, although the cluster addresses were effectively 16 bits, this does not fit the modern definition of the term "16-bit."

Because it was used for so long, multiple versions of the FAT16 file system were created throughout its lifespan, including FAT16B. However, the FAT file system quickly grew out of favor once its 32-bit counterpart was developed.

FAT32
After undergoing various iterations under the FAT16 umbrella, FAT was eventually upgraded to a 32-bit architecture in 1996. While this provided more than enough accommodations for computer systems at the time, its max volume size of 2 TB and the max volume size of 16 TB would prove to be limitations within 10 to 15 years after release.

exFAT
Introduced in 2006 and developed for Windows Embedded CE 6.0, exFAT was eventually transitioned to the Windows NT family of operating systems via separate service packs for Microsoft Vista and Windows XP. Although it is ultimately based on the FAT architecture, exFAT isn't compatible with any other versions of the FAT file system.

FATX
This version of FAT was developed specifically for the Microsoft Xbox video game console. There are two iterations, FATX16 and FATX32, which mirror many of the features and capabilities of their PC-oriented counterparts. Regardless of the similarities, FATX is not compatible with FAT.

Other Versions of FAT
There are other versions of the FAT file system, too. However, these are generally reserved for special uses. Turbo FAT, for example, is used exclusively with the NetWare OS. Regardless of the exact version you use, FAT serves as a means of storing, organizing, and managing your data. Without FAT - or another, similar file system - your system would be an inaccessible and completely inoperable.

You may read more about the FAT file system in Wikipedia: FAT.
Our article Data Recovery from a Re-Formatted exFAT/FAT Disk explains how to recover files from such disks.