What is a File Allocation Table (FAT)?

File Allocation Table (FAT) is a file system developed by Microsoft in 1977 and is still used today as the file system of choice for floppy drives and high-capacity portable storage devices such as flash drives and others. solid-state storage devices, such as SD Cards.

What is the FAT File System?

FAT was the primary file system used in all of Microsoft's consumer operating systems, from MS-DOS to Windows ME. Although FAT is still a supported option on newer Microsoft operating systems, NTFS is the primary file system in use today.

The file allocation table file system has progressed over time, largely due to the need to support larger disk drives and larger file sizes.

Let's dive into the different versions of the FAT file system.

FAT12 (12-bit File Allocation Table)

The first widely used version of the FAT file system, FAT12, was introduced in 1980 along with the first versions of DOS.

FAT12 was the primary file system for Microsoft operating systems up to MS-DOS 3.30, but was also used on most systems up to MS-DOS 4.0. It's still the file system occasionally used on floppies you'll find today.

This file system supports drive and file sizes up to 16 MB in 4 KB clusters or 32 MB in 8 KB clusters with a maximum of 4,084 files on a single volume (when using 8 KB clusters).

File names in FAT12 cannot exceed the maximum character limit of 8 characters plus three for the extension.

A number of file attributes were first introduced in FAT12, including the hidden, read-only, system, and volume label.

Note: FAT8, introduced in 1977, was the first real version of the FAT file system, but it saw limited use on some terminal-type computer systems at the time.

FAT16 (16-bit File Allocation Table)

The second implementation of FAT was FAT16, first introduced in 1984 in PC DOS 3.0 and MS-DOS 3.0.

A slightly improved version of FAT16 called FAT16B was the main file system for MS-DOS 4.0 until MS-DOS 6.22. Beginning with MS-DOS 7.0 and Windows 95, an enhanced version called FAT16X was used instead.

Depending on the operating system and the size of the cluster used, the maximum size of a FAT16-formatted drive can range from 2 GB to 16 GB, the latter only on Windows NT 4 with 256 KB clusters.

The maximum file size on FAT16 drives is 4 GB with large file support enabled or 2 GB without support.

A maximum of 65,536 files can be stored on a FAT16 volume. Like FAT12, file names were limited to 8+3 characters, but were extended to 255 characters starting with Windows 95.

The archive file attribute was introduced in FAT16.

FAT32 (32-bit File Allocation Table)

FAT32 is the latest version of the FAT file system. Introduced in 1996 for Windows 95 OSR2/MS-DOS 7.1 users, it was the primary file system for consumer versions of Windows through Windows ME.

Supports base drive sizes up to 2TB or even up to 16TB with 64KB clusters.

As with FAT16, the maximum file size for drives is 4 GB with large file support enabled or 2 GB without support. A modified version of this file system called FAT32+ supports files up to 256 GB in size!

Up to 268,173,300 files can be contained on a FAT32 volume as long as you use 32KB clusters.

exFAT (Extended File Allocation Table)

exFAT, first introduced in 2006, is another file system created by Microsoft, although it is not the "next" version of FAT after FAT32.

This is primarily designed for use in portable media devices like flash drives, SDHC and SDXC cards, etc. exFAT officially supports portable media storage devices up to 512 TiB in size, but could theoretically support drives up to 64 ZiB in size, which is considerably larger than any media available at the time of writing.

Built-in support for 255-character filenames and support for up to 2,796,202 files per directory are two notable features of the exFAT system.

The exFAT file system is supported by almost all versions of Windows (earlier versions with optional updates), Mac OS X (10.6.5+), as well as many televisions, media, and other devices.

Move Files From NTFS Systems to FAT

File encryption, file compression, object permissions, disk quotas, and indexed file attribute are only available for NTFS file system, not FAT. Other attributes like those mentioned in the above discussions are also available in NTFS.

Due to their differences, if you place an encrypted file on an NTFS volume in a FAT-formatted area, the file loses its encryption status, which means that the file can be used as a normal, unencrypted file. Decrypting a file in this way is only possible for the original user who encrypted the file or any other user who has received permission from the original owner.

Like encrypted files, a compressed file is automatically decompressed when it is copied from an NTFS volume to a FAT volume, since FAT does not support compression. For example, if you copy a compressed file from an NTFS disk to a FAT disk, the file will be automatically decompressed before being saved to the disk because the FAT file system on the destination media does not have the ability to store compressed files.

Advanced Reading on FAT

While this goes well beyond the basic discussion of FAT, if you'd like more information on how drives formatted in FAT12, FAT16, and FAT32 are structured, check out Andries E. Brouwer's FAT File System.