The FAT allocation system is primarly concerned with a descrete method of organizing files. In order to protect the file system, two copies are stored: FAT1 and FAT2. With two copies available redundancy is achieved in case one fails. The partition Boot Sector stores information critical to the file system. This information includes the number of sectors, and number of clustors, the number of sectors per cluster and more. When a computer user wants to read any type of file, the FAT file system also reassembles each piece of the file into one complete unit for viewing. The Root Folder contains a small piece of information for each file and directory in the system. Unlike other files in the system the Root Folder has a fixed size.
- FAT Partition Boot Sector
- FAT File System
- FAT Root Folder
- FAT Folder Structure
Originally developed by Bill Gates in 1976 as a way to store data on floppy disks for a version of Basic, the file allocation table system was quickly incorporated into an early version of Tim Patterson's (of Seattle Computer Products fame) operating system, QDOS ("Quick and Dirty Operating System"). Gates later bought the rights to QDOS and released it under Microsoft as PC-DOS and later, MS-DOS.
- FAT12 is the oldest type of FAT that uses a 12 bit file allocation table entry.
- FAT12 can hold a max of 4,086 clusters (which is 212 clusters minus a few values that are reserved for values used in the FAT).
- It is used for floppy disks and hard drive partitions that are smaller than 16 MB.
- All 1.4 MB 3.5 inch floppy disks are formatted using FAT12.
FAT32: FAT32 is the enhanced version of the FAT system implemented beginning with Windows 95 OSR2, Windows 98, and Windows Me. Features include:
- Drives of up to 2 terabytes are supported (Windows 2000 only supports up to 32 gigabytes)
- Since FAT32 uses smaller clusters (of 4 kilobytes each), it uses hard drive space more efficiently. This is a 10 to 15 percent improvement over FAT or FAT16.
- The limitations of FAT or FAT 16 on the number of root folder entries have been eliminated. In FAT32, the root folder is an ordinary cluster chain, and can be located anywhere on the drive.
- File allocation mirroring can be disabled in FAT32. This allows a different copy of the file allocation table then the default to be active.
Currently the FAT file system has become the ubiquitous format that is used for interchange of media between computers. Since the advent of less expensive, removable flash memory, the FAT file system has become the format that is used between digital devices. Some items in which you might find the FAT file format are:
- Thumb drives
- Portable digital still/video cameras
- Portable digital audio and video players
- Multifunction printers
- Electronic photo frames
- Electronic musical instruments
- Standard televisions
Comparison of FAT Versions'
Table adapted from: http://en.wikipedia.org/wiki/File_Allocation_Table
|Full Name||File Allocation Table|
|(12-bit version)||(16-bit version)||(32-bit version)|
|Introduced||1977 (Microsoft Disk BASIC)||July 1988 (MS-DOS 4.0)||August 1996 (Windows 95 OSR2)|
|Partition identifier||0x01 (MBR)||0x04, 0x06, 0x0E (MBR)||0x0B, 0x0C (MBR)
|File allocation||Linked List|
|Bad blocks||Linked List|
|Max file size||32 MiB||2 GiB||4 GiB|
|Max number of files||4,077||65,517||268,435,437|
|Max filename size||8.3 or 255 characters when using LFNs|
|Max volume size||32 MiB||4 GiB||2 TiB|
|Dates recorded||Creation, modified, access|
|Date range||January 1, 1980 - December 31, 2107|
|Attributes||Read-only, hidden, system, volume label, subdirectory, archive|
|Transparent compression||Per-volume, Stacker, DoubleSpace, DriveSpace||No|
|Transparent encryption||Per-volume only with DR-DOS||No|
Recovering directory entries from FAT filesystems as part of Recovering_deleted_data can be accomplished by looking for entries that begin with a sigma 0xe5. When a file or directory is deleted under a FAT filesystem, the first character of its name is changed to sigma. The remainder of the directory entry information remains intact.