The File Allocation Table (FAT) is a file service for storage clusters. FAT (File Allocation Table) is part of the file system of the DOS operating system and Windows 96/98 and divides hard disks into clusters, whereby a cluster consists of one or more sectors.
As the name implies, File Allocation Table (FAT) stands for a table containing the tables of contents of all file parts stored on a disk. Each cluster on the disk has an entry in the FAT table. The entries indicate the assignment of file parts to a cluster. Each file entry is concatenated with other file entries, starting with the first cluster. Since the first FAT allocation system could only handle eight-letter file names, there were some restrictions that were lifted by FAT16 and later by FAT32.
With FAT16, hard disks up to 2.048 gigabytes (GB) are divided into cluster sizes between 2 kilobytes (KB) for the 128 MB hard disk and 32 KB for the 2 GB hard disk. The FAT file system contains pointers to the clusters in which the file's information is kept on the storage medium. FAT16-based systems support disks of up to 8 gigabytes, which was increased to 2 terabytes (TB) in later versions for FAT32, based on Windows 95/98 and Windows NT
FAT32 uses small 4-KB clusters for drives and memory cards with capacities up to 8 GB. It thus uses the available storage space more efficiently than FAT16. It can manage volumes of up to 2 terabytes (TB), although the maximum size of a FAT32 partition is limited to 4 gigabytes (GB). The address space is 32 bits of which 4 bits are reserved.
OS/2 and the operating systems mentioned above support the FAT file system in addition to their own file systems High Performance File System (HPFS), New Technology File System (NTFS) and Virtual File Allocation Table (VFAT). For flash memory and external drives with a storage capacity of more than 2 GB, the FAT64 file system, also known as Extended File Allocation Table (exFAT), was developed. exFAT has an address space of 64 bits, which corresponds to an allocation of 16 exbi (egg). With exFAT, file sizes of up to 512 terabytes (TB) can be managed.