Even if only one byte of storage is needed to extend a file, an entire cluster must be allocated to it and any single cluster can not hold more than a single file, so large clusters waste much disk space if there are large numbers of small files. The maximum size of a file or a disk drive that can be accessed is the product of the largest number that can be stored in the entries (less a few values reserved to indicate unallocated space or the end of a list) and the size of the disk cluster. Sub-directories are implemented as special files containing the directory entries of their respective files.Įach entry in the FAT linked list is a fixed number of bits: 12, 16 or 32. The operating system can then traverse the FAT, looking up the cluster number of each successive part of the disk file as a cluster chain until the end of the file is reached. The root directory of the disk contains the number of the first cluster of each file in that directory. Each entry contains either the number of the next cluster in the file, or else a marker indicating the end of the file, unused disk space, or special reserved areas of the disk. The table is a linked list of entries for each cluster, a contiguous area of disk storage. The FAT is statically allocated at the time of formatting. The file system uses an index table stored on the device to identify chains of data storage areas associated with a file, the File Allocation Table ( FAT). Main article: Design of the FAT file system The DCF file system adopted by almost all digital cameras since 1998 defines a logical file system with 8.3 filenames and makes the use of either FAT12, FAT16, FAT32 or exFAT mandatory for its physical layer for compatibility. FAT is supported by portable devices such as PDAs, digital cameras, camcorders, media players, and mobile phones. The FAT file system is used in removable media such as floppy disks, super-floppies, memory and flash memory cards or USB flash drives. Microsoft Windows additionally comes with a pre-installed tool to convert a FAT file system into NTFS directly without the need to rewrite all files, though this cannot be reversed easily. Hidden FAT filesystems are also used in the UEFI boot partition on modern PCs.įAT is still used in drives expected to be used by multiple operating systems, such as in shared Windows, Linux and DOS environments. While FAT12 is used on floppy disks, FAT16 and FAT32 are typically found on the larger media.įAT is used internally for the EFI system partition in the boot stage of EFI-compliant computers. These standards cover FAT12 and FAT16 with only short 8.3 filename support long filenames with VFAT were partially patented. Windows Me was the final version of Windows to use FAT as its default file system.įor floppy disks, FAT has been standardized as ECMA-107 and ISO/ IEC 9293:1994 (superseding ISO 9293:1987 ). Microsoft introduced NTFS with the Windows NT platform in 1993, but FAT remained the standard for the home user until the introduction of Windows XP in 2001. Uses įAT was also used on hard disks throughout the DOS and Windows 9x eras. Nevertheless, FAT continues to be used on flash and other solid-state memory cards and modules (including USB flash drives), many portable and embedded devices because of its compatibility and ease of implementation. FAT was replaced with NTFS as the default file system on Microsoft operating systems starting with Windows XP. The increase in disk drives capacity required three major variants: FAT12, FAT16 and FAT32. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. FAT12/FAT16: Per-volume only with DR-DOSįile Allocation Table ( FAT) is a file system developed for personal computers and was the default filesystem for MS-DOS and Windows 9x operating systems.
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