File Allocation Table (FAT) is the earliest file system used for hard disks by the MS-DOS operating system.

Here are the versions of FAT:

• FAT12: FAT12 was introduced with early versions of MS-DOS. A 12-bit address for a FAT entry allows up to 4096 addresses. The cluster size for FAT12 can range from a single sector up to 4 KB. This allows for a maximum partition size of 16 MB. Windows 7 only uses this file system for floppy disks.
• FAT16: FAT16 is common to earlier operating systems where the partition size did not exceed 2 GB. A 16-bit address for a FAT entry allows up to 65,536 addresses. The cluster size for FAT16 is limited depending on the version of Windows. Windows NT, Windows 2000, Windows 2003, Windows Server 2008, Windows 7 and Windows Vista support a maximum cluster size of 64 KB with FAT16, which allows a maximum partition size of 4 GB. All other operating systems that support FAT16 only support a maximum cluster size of 32 KB, which allows a maximum partition size of 2 GB with FAT16.
• FAT32: FAT32 was introduced with Windows 95 OSR2 to support hard disks that were becoming much larger than 2 GB in size. The 32-bit address used for a FAT entry allows for more than 2 million addresses. The problem introduced by so many addresses is that the table used to keep track of them becomes very large and inefficient to manage. Windows XP, Windows Vista, and Windows 7 will not use FAT32 as a file system for new partitions or volumes larger than 32 GB. Additionally, files larger than 4 GB cannot be stored in a FAT32 file system.

Pre-existing partitions or volumes that are larger than 32 GB and formatted with FAT32 are still accessible to Windows 7.

One of the main advantages of FAT32 is its support for smaller cluster sizes, which results in more efficient space allocation than was possible with FAT16. Files stored on a FAT32 partition can use 20 to 30 percent less disk space than files stored on a FAT16 partition. FAT32 supports drive sizes from 512 MB up to 2 TB, although if you create and format a FAT32 partition through Windows 7, the FAT32 partition can only be up to 32 GB. Because of the smaller cluster sizes, FAT32 can also load programs up to 50 percent faster than programs loaded from FAT16 partitions.

The limitations of FAT include:

• Limited fault tolerance: There is no provision for fault-tolerance in FAT, except for the fact that two copies of the FAT table are stored in the partition.
• Inefficient storage: When a file's data is written to a cluster, the entire cluster is unavailable for any other file to store data in, even if the entire cluster is not used. Large cluster sizes can lead to a lot of wasted space.
• Limited security: Simple attributes are used to mark files as system files, hidden, or read only; no user-based security is available.

The benefits of FAT include:

• Supported by many legacy operating systems.
• Simple technology that is well understood and supported by third-party utilities.
• Adequate when file and folder requirements are simple and do not require complex security.
• Suitable for removable media such as digital camera memory, media players, and USB.

The main disadvantages of FAT32 compared to NTFS are that it does not provide as much support for larger hard drives and it does not provide very robust security options. It also offers no native support for disk compression.