| | | | File Allocation Table. A file system that Microsoft developed, in the first place, for MS-DOS in 1977 (and that has since come to be known as FAT12 because cluster addresses are 12 bits long) that was used also in revised forms in the first release of Windows versions 95 as FAT16 (cluster addresses of 16 bits). Windows 95 OSR2, Windows 98, Me 2000 and XP use FAT32 with a possible 32-bit cluster address, of which 28 are currently used (although the latter two also use NTFS). The file allocation table maintains a record of where about on a hard, floppy or flash disk the clusters of data that make up a file are stored (clusters are not always contiguous, because of fragmentation). When the computer needs to use a file, it reads the FAT to determine whereabouts the different clusters are located then reassembles them into an entire file. The directory table file stores information about the address of the first cluster for each file (if there is more than one cluster). The second cluster's entry has data about the location of the third cluster etc. The entry for the last cluster contains an end of file code. FAT16 supports 16-bit cluster addresses and maximum partition sizes of up to 2GB. With FAT32 that limit is increased to a theoretical 8TB (TeraBytes) although in practice this is limited to 2TB by the boot sector. File size is still a limiting factor under even FAT32 though, with the maximum file size being 4GB (not unusual these days especially in the case of video files for example). Current "Windows PCs" generally ship with a version of NTFS (Windows NT File System) such as XP or Vista in most cases, removing this restriction and servers running a Microsoft OS with Windows Server 2003 or 2008. | | | |
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