FAT is an abbreviation of the File Allocation Table. It is a table marking the position of files. It is very important for the use of the hard disk. If FAT is lost, the data on the hard disk can not be used because it is unable to be located. File systems of different operating systems are different. In the operating system of the personal computer, FAT16 is used in MS-DOS and low-level versions; HPFS is used in OS/2, and NTFS is used in Windows NT. And MS-DOS 7. 10 and ROM-DOS 7. 10 both provide FAT16 and FAT32 for users. The most file system we contact is FAT16 and FAT32. As a 16-bit file system, FAT16 can map a maximum of 65,526 clusters. Like most Windows file systems, FAT16 supports a variety of cluster sizes, allowing it to be used on hard disks that are as small as 16 MB or as large as 2 GB. A later revision to the file system allowed it to support volumes up to 4 GB. FAT16 was created long ago, it has inherent limitations that make it largely unsuitable for use on modern operating systems.