The file allocation table (FAT) file system is the simplest of all the file systems and is supported by all Windows operating systems. The FAT file system (also known as FAT-16) is a leftover from the MS-DOS operating system. As its name suggests, the FAT file system merely stores a table (and a backup table) of all the files and their positions on the disk. The table is stored at the beginning of a disk volume and must be updated whenever files are added or modified. New data is just allocated to slots large enough to contain it, which leads to high fragmentation. This simplicity leads to poor performance and limited robustness. The maximum size of a FAT file system is 4GB under Windows NT, but performance is seriously degraded for file systems larger than 2GB. Note The FAT file system originally was limited to 32MB partitions, until MS-DOS 4 increased the size of the FAT entries. The basic FAT filenames are limited to eight characters, followed by a dot, and then a three-letter suffix. All lowercase letters in filenames are converted to uppercase letters when stored. Longer filenames are truncated and made unique by conversion to a six-character name, followed by a tilde and an autogenerated number to preserve uniqueness. FAT file systems support only the very basic file attributes (such as read-only, archive, hidden, and system). No security attributes or permissions can be assigned to files on a FAT file system. It is unusual for modern Windows versions to create pure FAT file systems for their main hard drive partitions. But older systems (including early versions of Windows 95) still may use and preserve FAT file systems. Also, floppy disks still use FAT (protected mode), because it is the common denominator for file interchange and has a small footprint for small volume sizes (such as the common 1.44MB floppy disk standard).
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