| Developer(s) | Microsoft,NCR,SCP,IBM,Compaq,Digital Research,Novell,Caldera |
|---|---|
| Full name | File Allocation Table |
| Variants | 8-bit FAT,FAT12,FAT16,FAT16B,FAT32,exFAT,FATX,FAT+ |
| Introduced | 1977 (1977) withStandalone Disk BASIC-80 |
| Partition IDs | MBR/EBR: |
| Structures | |
| Directory contents | Table |
| File allocation | Linked list |
| Bad blocks | Cluster tagging |
| Limits | |
| Max volume size |
|
| Max file size | 4,294,967,295 bytes (4 GB − 1) with FAT16B and FAT32[1] |
| Maxno. of files |
|
| Max filename length | 8.3 filename, or 255UCS-2 characters when usingLFN[nb 1] |
| Features | |
| Dates recorded | |
| Date range | 1980-01-01 to2099-12-31 (2107-12-31) |
| Date resolution |
|
| Forks | Not natively |
| Attributes | Read-only, hidden, system, volume, directory, archive |
| File system permissions |
|
| Transparent compression |
|
| Transparent encryption |
|
File Allocation Table (FAT) is afile system developed for personal computers and was the default file system for theMS-DOS andWindows 9x operating systems.[citation needed] Originally developed in 1977 for use onfloppy disks, it was adapted for use onhard disks and other devices. The increase in disk drive capacity over time drove modifications to the design that resulted in versions:FAT12,FAT16,FAT32, andexFAT. FAT was replaced withNTFS as the default file system on Microsoft operating systems starting withWindows XP.[3] Nevertheless, FAT continues to be commonly used on relatively small capacitysolid-state storage technologies such asSD card,MultiMediaCard (MMC) andeMMC because of its compatibility and ease of implementation.[4]
FAT was used onhard disks throughout theDOS andWindows 9x eras. Microsoft introducedNTFS with theWindows NT platform in 1993, but FAT remained the standard for the home user until the introduction ofWindows XP in 2001.Windows Me was the final version ofWindows to use FAT as its default file system.
For floppy disks, FAT has been standardized asECMA-107[5] andISO/IEC 9293:1994[6] (superseding ISO 9293:1987[7]). These standards cover FAT12 and FAT16 with only short8.3 filename support;long filenames withVFAT were partiallypatented.[8] WhileFAT12 is used on floppy disks,FAT16 andFAT32 are typically found on the larger media.
FAT is used internally for theEFI system partition in the boot stage ofEFI-compliant computers.[9]
FAT is still used in drives expected to be used by multiple operating systems, such as in shared Windows,Linux and DOS environments. 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.[10] The FAT file system is used in removable media such asfloppy disks,super-floppies,memory andflash memory cards orUSB flash drives. FAT is supported by portable devices such asPDAs,digital cameras,camcorders,media players, and mobile phones.[citation needed]
TheDCF file system adopted by almost alldigital cameras since 1998 defines a logical file system with8.3 filenames and makes the use of either FAT12, FAT16, FAT32 or exFAT mandatory for its physical layer for compatibility.[11]
The file system uses an index table stored on the device to identify chains of data storage areas associated with a file, theFile Allocation Table (FAT). The FAT is statically allocated at the time of formatting. The table is alinked list of entries for eachcluster, a contiguous area of disk storage. 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. Theroot directory of the disk contains the number of the first cluster of each file in that directory. The operating system can then traverse the FAT, looking up the cluster number of each successive part of the disk file as acluster chain until the end of the file is reached.Sub-directories are implemented as special files containing thedirectory entries of their respective files.
Each entry in the FAT linked list is a fixed number of bits: 12, 16 or 32. 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. Even if only one byte of storage is needed to extend a file, an entire cluster must be allocated to it. As a result, large numbers of small files can result in clusters being allocated that may contain mostly "empty" data to meet the minimum cluster size.
Originally designed as an 8-bit file system, the maximum number of clusters must increase as disk drive capacity increases, and so the number of bits used to identify each cluster has grown. The successive major variants of the FAT format are named after the number of table element bits: 12 (FAT12), 16 (FAT16), and 32 (FAT32).
There are several variants of the FAT file system (e.g.FAT12,FAT16 andFAT32). FAT16 refers to both the original group of FAT file systems with 16-bit wide cluster entries and also to later variants. "VFAT" is an optional extension for long file names, which can work on top of any FAT file system. Volumes using VFAT long-filenames can be read also by operating systems not supporting the VFAT extension.
| Developer(s) | Microsoft,NCR,SCP |
|---|---|
| Full name | 8-bit File Allocation Table |
| Introduced |
|
| Limits | |
| Max file size | 8 MB |
| File size granularity | record-granularity (128 bytes)[12][13] |
| Max filename length | 6.3 filename (binary files), 9 characters (ASCII files)[12][13] |
| Max directory depth | No sub-directories |
| Allowed filename characters | ASCII (0x00 and0xFF not allowed in first character)[12][13] |
| Features | |
| Dates recorded | No |
| Attributes | Write protected,EBCDIC conversion, read after write, binary (random rather than sequential file)[12][13] |
The original FAT file system (orFAT structure, as it was called initially) was designed and implemented byMarc McDonald,[14] based on a series of discussions between McDonald andBill Gates.[14]It was introduced with8-bit table elements[12][13][14] (and valid data cluster numbers up to0xBF[12][13]) in a precursor toMicrosoft'sStandalone Disk BASIC-80 for an8080-based successor[nb 2] of theNCR 7200 model VI data-entry terminal, equipped with 8-inch (200 mm) floppy disks, in 1977[15] or 1978.[nb 2]In 1978,Standalone Disk BASIC-80 was ported to the8086 using an emulator on a DECPDP-10,[16] since no real 8086 systems were available at this time.The FAT file system was also used in Microsoft'sMDOS/MIDAS,[14] anoperating system for 8080/Z80 platforms written by McDonald since 1979.TheStandalone Disk BASIC version supported three FATs,[12][13][17] whereas this was a parameter for MIDAS. Reportedly, MIDAS was also prepared to support 10-bit, 12-bit and 16-bit FAT variants. While the size of directory entries was 16 bytes inStandalone Disk BASIC,[12][13] MIDAS instead occupied 32 bytes per entry.
Tim Paterson ofSeattle Computer Products (SCP) was first introduced to Microsoft's FAT structure when he helpedBob O'Rear adapting theStandalone Disk BASIC-86 emulator port onto SCP'sS-100 bus 8086CPU board prototype during a guest week at Microsoft in May 1979.[16] The final product was shown atLifeboat Associates' booth stand at theNational Computer Conference in New York[16] on June 4–7, 1979, where Paterson learned about the more sophisticated FAT implementation in MDOS/MIDAS[14] and McDonald talked to him about the design of the file system.[15]
| Developer(s) | SCP,Microsoft,IBM,Digital Research,Novell |
|---|---|
| Full name | 12-bit File Allocation Table |
| Introduced |
|
| Partition IDs | MBR/EBR: |
| Limits | |
| Max volume size |
|
| Max file size | Limited by volume size |
| File size granularity | 1 byte |
| Maxno. of files | 4,068 for 8 KB clusters |
| Max filename length | 8.3 filename withOEM characters, 255UCS-2 characters[nb 1] when usingLFN |
| Max directory depth | 32 levels or 66 characters (withCDS), 60 levels or more (without CDS) |
| Features | |
| Dates recorded | |
| Date range | 1980-01-01 to2099-12-31 (2107-12-31) |
| Date resolution |
|
| Attributes | Read-only (since DOS 2.0),hidden,system,volume (sinceMS-DOS 1.28 andPC DOS 2.0),directory (sinceMS-DOS 1.40 and PC DOS 2.0),archive (since DOS 2.0) |
| File system permissions |
|
| Transparent compression | Per-volume,SuperStor,Stacker,DoubleSpace,DriveSpace |
| Transparent encryption | Per-volume only withDR-DOS |
Between April and August 1980, while borrowing the FAT concept for SCP's own 8086 operating systemQDOS 0.10,[16] Tim Paterson extended the table elements to12 bits,[18] reduced the number of FATs to two, redefined the semantics of some of the reserved cluster values, and modified the disk layout, so that the root directory was now located between the FAT and the data area for his implementation ofFAT12. Paterson also increased the nine-character (6.3) filename[12][13] length limit to eleven characters to supportCP/M-style8.3 filenames andFile Control Blocks. The format used in MicrosoftStandalone Disk BASIC's 8-bit file system precursor was not supported by QDOS. By August 1980, QDOS had been renamed to86-DOS.[19] Starting with86-DOS 0.42, the size and layout of directory entries was changed from 16 bytes to 32 bytes[20] in order to add a file date stamp[20] and increase the theoretical file size limit beyond the previous limit of 16 MB.[20]86-DOS 1.00 became available in early 1981. Later in 1981, 86-DOS evolved into Microsoft'sMS-DOS andIBMPC DOS.[14][18][21]The capability to read previously formatted volumes with 16-byte directory entries[20] was dropped withMS-DOS 1.20.
FAT12 used 12-bit entries for the cluster addresses; some values were reserved to mark the end of a chain of clusters, to mark unusable areas of the disk, or for other purposes, so the maximum number of clusters was limited to 4078.[22][23] To conserve disk space, two 12-bit FAT entries used three consecutive 8-bit bytes on disk, requiring manipulation to unpack the 12-bit values. This was sufficient for the original floppy disk drives, and small hard disks up to 32 megabytes. TheFAT16B version available with DOS 3.31 supported32-bit sector numbers, and so increased the volume size limit.
All the control structures fit inside the first track, to avoid head movement during read and write operations. Any bad sector in the control structures area would make the disk unusable. The DOS formatting tool rejected such disks completely. Bad sectors were allowed only in the file data area. Clusters containing bad sectors were marked unusable with the reserved value0xFF7 in the FAT.
While 86-DOS supported three disk formats (250.25 KB, 616 KB and 1232 KB, withFAT IDs0xFF and0xFE) on 8-inch (200 mm) floppy drives, IBMPC DOS 1.0, released with the originalIBM Personal Computer in 1981, supported only an 8-sector floppy format with a formatted capacity of 160 KB (FAT ID0xFE) for single-sided 5.25-inch floppy drives, andPC DOS 1.1 added support for adouble-sided format with 320 KB (FAT ID0xFF).PC DOS 2.0 introduced support for 9-sector floppy formats with 180 KB (FAT ID0xFC) and 360 KB (FAT ID0xFD).
86-DOS 1.00 and PC DOS 1.0 directory entries included only one date, the last modified date. PC DOS 1.1 added the last modified time. PC DOS 1.xfile attributes included a hidden bit and system bit, with the remaining six bits undefined. At this time, DOS did not support sub-directories, but typically there were only a few dozen files on adiskette.
ThePC XT was the first PC with an IBM-supplied hard drive, and PC DOS 2.0 supported that hard drive with FAT12 (FAT ID0xF8). The fixed assumption of 8 sectors per clusters on hard disks practically limited the maximum partition size to 16 MB for 512 byte sectors and 4 KB clusters.
TheBIOS Parameter Block (BPB) was introduced with PC DOS 2.0 as well, and this version also added read-only,archive,volume label, anddirectory attribute bits for hierarchical sub-directories.[24]
MS-DOS 3.0 introduced support for high-density 1.2 MB 5.25-inch diskettes (media descriptor0xF9), which notably had 15 sectors per track, hence more space for the FATs.
FAT12 remains in use on all commonfloppy disks, including 1.44 MB and later 2.88 MB disks (media descriptor byte0xF0).
| Developer(s) | Microsoft,IBM,Digital Research,Novell |
|---|---|
| Full name | 16-bit File Allocation Table (with 16-bit sector entries) |
| Introduced | 1984-08-14 (PC DOS 3.0) 1984-08 (MS-DOS 3.0) |
| Partition IDs | MBR/EBR: |
| Limits | |
| Max file size | 4,294,967,295 bytes (4 GB − 1) |
| File size granularity | 1 byte |
| Maxno. of files | 65,536 for 32 KB clusters |
| Max filename length | 8.3 filename withOEM characters, 255 UCS-2 characters[nb 1] when usingLFN |
| Max directory depth | 32 levels or 66 characters (withCDS), 60 levels or more (without CDS) |
| Features | |
| Dates recorded | |
| Date range | 1980-01-01 to2099-12-31 (2107-12-31) |
| Date resolution |
|
| Attributes | Read-only,hidden,system,volume,directory,archive |
| File system permissions |
|
| Transparent compression | Per-volume,SuperStor,Stacker,DoubleSpace,DriveSpace |
| Transparent encryption | Per-volume only withDR-DOS |
In 1984, IBM released thePC AT, which required PC DOS 3.0 to access its 20 MB hard disk.[25][26] Microsoft introduced MS-DOS 3.0 in parallel. Cluster addresses were increased to 16-bit, allowing for up to 65,526 clusters per volume. However, the maximum possible number of sectors and the maximumpartition size of 32 MB did not change. Although cluster addresses were 16 bits, this format was not what today is commonly understood asFAT16.Apartition type0x04 indicates this form of FAT16 with less than 65,536 sectors (less than 32 MB for sector size 512). The benefit of FAT16 was the use of smaller clusters, making disk usage more efficient, particularly for large numbers of files only a few hundred bytes in size.
As MS-DOS 3.0 formatted all 16 MB-32 MB partitions in the FAT16 format, a 20 MB hard disk formatted under MS-DOS 3.0 was not accessible by MS-DOS 2.0.[27] MS-DOS 3.0 to MS-DOS 3.30 could still access FAT12 partitions under 15 MB, but required all 16 MB-32 MB partitions to be FAT16, and so could not access MS-DOS 2.0 partitions in this size range. MS-DOS 3.31 and higher could access 16 MB-32 MB FAT12 partitions again.
MS-DOS and PC DOS implementations of FAT12 and FAT16 could not access disk partitions larger than 32 megabytes. Several manufacturers developed their own FAT variants within their OEM versions of MS-DOS.[28]
Some vendors (AST andNEC[28]) supportedeight, instead of the standardfour, primary partition entries in their custom extendedMaster Boot Record (MBR), and they adapted MS-DOS to use more than a single primary partition.
Other vendors worked around the volume size limits imposed by the 16-bit sector entries by increasing the apparentsize of the sectors the file system operated on. Theselogical sectors were larger (up to 8192 bytes) than thephysical sector size (still 512 bytes) on the disk. The DOS-BIOS or System BIOS would then combine multiple physical sectors into logical sectors for the file system to work with.
These changes were transparent to the file system implementation in the DOS kernel. The underlying DOS-BIOS translated these logical sectors into physical sectors according to partitioning information and the drive's physical geometry.
The drawback of this approach was increased memory used for sector buffering and deblocking. Since older DOS versions could not use large logical sectors, the OEMs introduced new partition IDs for their FAT variants in order to hide them from off-the-shelf issues of MS-DOS and PC DOS. Known partition IDs for logical sectored FATs include:0x08 (Commodore MS-DOS 3.x),0x11 (Leading Edge MS-DOS 3.x),0x14 (AST MS-DOS 3.x),0x24 (NEC MS-DOS 3.30[28]),0x56 (AT&T MS-DOS 3.x),0xE5 (Tandy MS-DOS),0xF2 (Sperry IT MS-DOS 3.x,Unisys MS-DOS 3.3 – also used byDigital ResearchDOS Plus 2.1).[29] OEM versions like Toshiba MS-DOS, Wyse MS-DOS 3.2 and 3.3,[30] as well as Zenith MS-DOS are also known to have utilized logical sectoring.[31]
While non-standard and sub-optimal, these FAT variants are perfectly valid according to the specifications of the file system itself.[citation needed] Therefore, even if default issues of MS-DOS and PC DOS were not able to cope with them, most of these vendor-specific FAT12 and FAT16 variants can be mounted by more flexible file system implementations in operating systems such as DR-DOS, simply by changing the partition ID to one of the recognized types.[nb 3] Also, if they no longer need to be recognized by their original operating systems, existing partitions can be "converted" into FAT12 and FAT16 volumes more compliant with versions of MS-DOS/PC DOS 4.0–6.3, which do not support sector sizes different from 512 bytes,[32] by switching to aBPB with 32-bit entry for the number of sectors, as introduced since DOS 3.31 (seeFAT16B below), keeping the cluster size and reducing thelogical sector size in the BPB down to 512 bytes, while at the same time increasing the counts of logical sectors per cluster, reserved logical sectors, total logical sectors, and logical sectors per FAT by the same factor.
A parallel development in MS-DOS / PC DOS which allowed an increase in the maximum possible FAT size was the introduction of multiple FAT partitions on a hard disk. To allow the use of more FAT partitions in a compatible way, a new partition type was introduced in PC DOS 3.2 (1986), theextended partition (EBR),[14] which is a container for an additional partition calledlogical drive. Since PC DOS 3.3 (April 1987), there is another, optional extended partition containing the nextlogical drive, and so on. TheMBR of a hard disk can either define up to four primary partitions, or an extended partition in addition to up to three primary partitions.
| Developer(s) | Compaq,Digital Research,IBM,Microsoft,Novell |
|---|---|
| Full name | 16-bit File Allocation Table (with 32-bit sector entries) |
| Introduced |
|
| Partition IDs | MBR/EBR: |
| Limits | |
| Min volume size | |
| Max volume size | |
| Max file size | |
| File size granularity | 1 byte |
| Maxno. of files | 65,460 for 32 KB clusters |
| Max filename length | 8.3 filename withOEM characters, 255UCS-2 characters[nb 1] when usingLFN |
| Max directory depth | 32 levels or 66 characters (withCDS), 60 levels or more (without CDS) |
| Features | |
| Dates recorded | |
| Date range | 1980-01-01 to2099-12-31 (2107-12-31) |
| Date resolution |
|
| Attributes | Read-only,hidden,system,volume,directory,archive |
| File system permissions |
|
| Transparent compression | Per-volume,SuperStor,Stacker,DoubleSpace,DriveSpace |
| Transparent encryption | Per-volume only withDR-DOS |
In November 1987,Compaq Personal Computer DOS 3.31 (a modified OEM version of MS-DOS 3.3 released by Compaq with their machines) introduced what today is simply known asthe FAT16 format, with the expansion of the 16-bit disk sector count to 32 bits in the BPB.Although the on-disk changes were minor, the entire DOS disk driver had to be converted to use 32-bit sector numbers, a task complicated by the fact that it was written in 16-bitassembly language.The result was initially called theDOS 3.31 Large File System.Microsoft'sDSKPROBE tool refers to type0x06 asBigFAT,[34] whereas some older versions ofFDISK described it asBIGDOS. Technically, it is known asFAT16B.
Since older versions of DOS were not designed to cope with more than 65,535 sectors, it was necessary to introduce a new partition type for this format in order to hide it from pre-3.31 issues of DOS. The original form of FAT16 (with less than 65,536 sectors) had apartition type0x04. To deal with disks larger than this, type0x06 was introduced to indicate 65,536 or more sectors. In addition to this, the disk driver was expanded to cope with more than 65,535 sectors as well. The only other difference between the original FAT16 and the newer FAT16B format is the usage of anewer BPB format with 32-bit sector entry. Therefore, newer operating systems supporting the FAT16B format can cope also with the original FAT16 format without any necessary changes.
If partitions to be used by pre-DOS 3.31 issues of DOS need to be created by modern tools, the only criteria theoretically necessary to meet are a sector count of less than 65536, and the usage of the old partition ID (0x04). In practice however, type0x01 and0x04 primary partitions should not be physically located outside the first 32 MB of the disk, due to other restrictions in MS-DOS 2.x, which could not cope with them otherwise.
In 1988, the FAT16B improvement became more generally available throughDR DOS 3.31, PC DOS 4.0,OS/2 1.1, and MS-DOS 4.0. The limit on partition size was dictated by the 8-bitsigned count of sectors per cluster, which originally had a maximum power-of-two value of 64. With the standard hard disk sector size of 512 bytes, this gives a maximum of 32 KB cluster size, thereby fixing the "definitive" limit for the FAT16 partition size at 2 GB for sector size 512. Onmagneto-optical media, which can have 1 or 2 KB sectors instead of 0.5 KB, this size limit is proportionally larger.
Much later,Windows NT increased the maximum cluster size to 64 KB, by considering the sectors-per-cluster count as unsigned. However, the resulting format was not compatible with any other FAT implementation of the time, and it generated greaterinternal fragmentation.Windows 98, SE and ME also supported reading and writing this variant, but its disk utilities did not work with it and someFCB services are not available for such volumes. This contributes to a confusing compatibility situation.
Prior to 1995, versions of DOS accessed the disk viaCHS addressing only. WhenWindows 95(MS-DOS 7.0) introducedLBA disk access, partitions could start being physically located outside the first c. 8 GB of this disk and thereby out of the reach of the traditional CHS addressing scheme. Partitions partially or fully located beyond the CHS barrier therefore had to be hidden from non-LBA-enabled operating systems by using the new partition type0x0E in the partition table instead. FAT16 partitions using this partition type are also namedFAT16X.[35] The only difference, compared to previous FAT16 partitions, is the fact that some CHS-related geometry entries in the BPB record, namely the number of sectors per track and the number of heads, may contain no or misleading values and should not be used.
The number of root directory entries available for FAT12 and FAT16 is determined when the volume is formatted, and is stored in a 16-bit field. For a given numberRDE and sector sizeSS, the numberRDS of root directory sectors isRDS = ceil((RDE × 32) / SS), andRDE is normally chosen to fill these sectors, i.e.,RDE × 32 = RDS × SS. FAT12 and FAT16 media typically use 512 root directory entries on non-floppy media. Some third-party tools, like mkdosfs, allow the user to set this parameter.[36]
| Developer(s) | Microsoft,Caldera |
|---|---|
| Introduced | August 1996 (Windows 95 OSR2) |
| Partition IDs | MBR/EBR: |
| Limits | |
| Min volume size | |
| Max volume size |
|
| Max file size | |
| File size granularity | 1 byte |
| Maxno. of files | 268,173,300 for 32 KB clusters |
| Max filename length | 8.3 filename withOEM characters, 255UCS-2 characters[nb 1] when usingLFN |
| Max directory depth | 32 levels or 66 characters (withCDS), 60 levels or more (without CDS) |
| Features | |
| Dates recorded | |
| Date range | 1980-01-01 to2099-12-31 (2107-12-31) |
| Date resolution |
|
| Attributes | Read-only,hidden,system,volume,directory,archive |
| File system permissions | Partial, only withDR-DOS,REAL/32 and4690 OS |
| Transparent compression | Yes |
In order to overcome the volume size limit of FAT16, while at the same time allowing DOSreal-mode code to handle the format, Microsoft designed a new version of the file system,FAT32, which supported an increased number of possible clusters, but could reuse most of the existing code, so that theconventional memory footprint was increased by less than 5 KB under DOS.[37] Cluster values are represented by32-bit numbers, of which 28 bits are used to hold the cluster number.
The FAT32 boot sector uses a 32-bit field for the sector count, limiting the maximal FAT32 volume size to 2 terabytes with a sector size of 512 bytes. The maximum FAT32 volume size is 16 TB with a sector size of 4,096 bytes.[38][39] The built-inWindows shell disk format tool on Windows NT arbitrarily only supports volume sizes up to 32 GB,[nb 4] but Windows supports reading and writing to preexisting larger FAT32 volumes, and these can be created with thecommand prompt,PowerShell or third-party tools,[41] or by formatting the volume on a non-Windows system or on a Windows 9x system with FAT32 support and then transferring it to the Windows NT system. In August 2024, Microsoft released an update to Windows 11 preview builds that allows for the creation of FAT32 partitions up to 2TB in size.[42]
The maximal possible size for a file on a FAT32 volume is 4 GB minus 1 byte, or 4,294,967,295 (232 − 1) bytes. This limit is a consequence of the 4-byte file length entry in the directory table and would also affect relatively huge FAT16 partitions enabled by a sufficient sector size.
Like FAT12 and FAT16, FAT32 does not include direct built-in support for long filenames, but FAT32 volumes can optionally holdVFAT long filenames in addition to short filenames in exactly the same way as VFAT long filenames have been optionally implemented for FAT12 and FAT16 volumes.
FAT32 was introduced withWindows 95 OSR2(MS-DOS 7.1) in 1996, although reformatting was needed to use it, andDriveSpace 3 (the version that came with Windows 95 OSR2 and Windows 98) never supported it.Windows 98 introduced a utility to convert existing hard disks from FAT16 to FAT32 without loss of data.
In the Windows NT line, native support for FAT32 arrived inWindows 2000. A free FAT32 driver forWindows NT 4.0 was available fromWinternals, a company later acquired by Microsoft. The acquisition of the driver from official sources is no longer possible. Since 1998, Caldera's dynamically loadableDRFAT32 driver could be used to enable FAT32 support in DR-DOS.[43][44] The first version of DR-DOS to natively support FAT32 and LBA access was OEM DR-DOS 7.04 in 1999. That same yearIMS introduced native FAT32 support withREAL/32 7.90, andIBM 4690 OS added FAT32 support with version 2.[45]Ahead Software provided another dynamically loadable FAT32.EXE driver for DR-DOS 7.03 withNero Burning ROM in 2004. IBM introduced native FAT32 support with OEM PC DOS 7.1 in 1999.
Two partition types have been reserved for FAT32 partitions,0x0B and0x0C. The latter type is also namedFAT32X in order to indicate usage of LBA disk access instead of CHS.[43][46][47][48][49] On such partitions, CHS-related geometry entries, namely theCHS sector addresses in the MBR as well as the number ofsectors per track and thenumber of heads in the EBPB record, may contain no or misleading values and should not be used.[50][48][49]
OS/2 heavily depends onextended attributes (EAs) and stores them in a hidden file called "EA␠DATA.␠SF" in theroot directory of theFAT12 orFAT16 volume. This file is indexed by two previously reserved bytes in the file's (or directory's)directory entry at offset0x14.[51] In theFAT32 format, these bytes hold the upper 16 bits of the starting cluster number of the file or directory, hence making it impossible to storeOS/2 EAs on FAT32 using this method.
However, the third-party FAT32installable file system (IFS) driver FAT32.IFS version 0.70 and higher by Henk Kelder & Netlabs for OS/2,eComStation andArcaOS stores extended attributes in extra files with filenames having the string "␠EA.␠SF" appended to the regular filename of the file to which they belong. The driver also utilizes the byte at offset0x0C in directory entries to store a special mark byte indicating the presence of extended attributes to help speed up things.[52][53] (This extension is critically incompatible with the FAT32+ method to store files larger than 4 GB minus 1 on FAT32 volumes.)[33]
Extended attributes are accessible via theWorkplace Shell desktop, throughREXX scripts, and many systemGUI andcommand-line utilities (such as4OS2).[54]
To accommodate itsOS/2 subsystem,Windows NT supports the handling of extended attributes inHPFS,NTFS, FAT12 and FAT16. It stores EAs on FAT12, FAT16 and HPFS using exactly the same scheme as OS/2, but does not support any other kind ofADS as held on NTFS volumes. Trying to copy a file with any ADS other than EAs from an NTFS volume to a FAT or HPFS volume gives a warning message with the names of the ADSs that will be lost. It does not support the FAT32.IFS method to store EAs on FAT32 volumes.
Windows 2000 onward acts exactly as Windows NT, except that it ignores EAs when copying to FAT32 without any warning (but shows the warning for other ADSs, like "Macintosh Finder Info" and "Macintosh Resource Fork").
Cygwin uses "EA␠DATA.␠SF" files as well.
One of theuser experience goals for the designers ofWindows 95 was the ability to uselong filenames (LFNs—up to 255UTF-16code units long),[nb 1] in addition to classic8.3 filenames (SFNs). Forbackward andforward compatibility, LFNs were implemented as an optional extension on top of the existing FAT file system structures using aworkaround in the way directory entries are laid out.
This transparent method to store long file names in the existing FAT file systems without altering their data structures is usually known asVFAT (for "Virtual FAT") after the Windows 95virtual device driver.[nb 5]
Non VFAT-enabled operating systems can still access the files under their short file name alias without restrictions; however, the associated long file names may be lost when files with long filenames are copied under non VFAT-aware operating systems.
In Windows NT, support for VFAT long filenames began with version3.5.
Linux provides a VFAT filesystem driver to work with FAT volumes with VFAT long filenames. For some time, aUVFAT driver was available to provide combined support forUMSDOS-style permissions with VFAT long filenames.
OS/2 added long filename support to FAT usingextended attributes (EA) before the introduction of VFAT. Thus, VFAT long filenames are invisible to OS/2, and EA long filenames are invisible to Windows; therefore, experienced users of both operating systems would have to manually rename the files.
Human68K supported up to18.3 filenames and (Shift JIS)Kanji characters in a proprietary FAT file system variant.
In order to supportJava applications, theFlexOS-basedIBM 4690 OS version 2 introduced its ownvirtual file system (VFS) architecture to store long filenames in the FAT file system in a backwards-compatible fashion. If enabled, the virtual filenames (VFN) are available under separate logical drive letters, whereas the real filenames (RFN) remain available under the original drive letters.[55]
The FAT file system itself is not designed for supportingalternate data streams (ADS), but some operating systems that heavily depend on them have devised various methods for handling them on FAT volumes. Such methods either store the additional information in extra files and directories (classic Mac OS andmacOS), or give new semantics to previously unused fields of the FAT on-disk data structures (OS/2 andWindows NT).
Mac OS usingPC Exchange stores its various dates, file attributes and long filenames in ahidden file called "FINDER.DAT", andresource forks (a common Mac OS ADS) in a subdirectory called "RESOURCE.FRK", in every directory where they are used. From PC Exchange 2.1 onwards, they store the Mac OS long filenames as standard FAT long filenames and convert FAT filenames longer than 31 characters to unique 31-character filenames, which can then be made visible to Macintosh applications.
macOS storesresource forks and metadata (file attributes, other ADS) usingAppleDouble format in a hidden file with a name constructed from the owner filename prefixed with "._", andFinder stores some folder and file metadata in a hidden file called ".DS_Store" (but note that Finder uses.DS_Store even on macOS' native filesystem,HFS+).
Early Linux distributions also supported a format known asUMSDOS, a FAT variant with Unix file attributes (such as long file name and access permissions) stored in a separate file called "--linux-.---". UMSDOS fell into disuse afterVFAT was released and it is not enabled by default inLinux from version 2.5.7 onwards.[56] For some time, Linux also provided combined support for UMSDOS-style permissions and VFAT long filenames throughUVFAT.
In 2007 the openFAT+ draft proposed how to storelarger files up to 256 GB minus 1 byte, or 274,877,906,943 (238 − 1) bytes, on slightly modified and otherwise backward-compatible FAT32 volumes,[33] but imposes a risk that disk tools or FAT32 implementations not aware of this extension may truncate or delete files exceeding the normal FAT32 file size limit. Support forFAT32+ andFAT16+ is limited to some versions ofDR-DOS and not available in mainstream operating systems.[57] (This extension is critically incompatible with the/EAS option of the FAT32.IFS method to storeOS/2 extended attributes on FAT32 volumes.)
In itsNetWare File System (NWFS)Novell implemented a heavily modified variant of a FAT file system for theNetWare operating system. For larger files it utilized a performance feature namedTurbo FAT.
FATX is a family of file systems designed forMicrosoft'sXboxvideo game consolehard disk drives andmemory cards,[58][59] introduced in 2001.
While resembling the same basic design ideas asFAT16 andFAT32, theFATX16 andFATX32 on-disk structures are simplified, but fundamentally incompatible with normal FAT16 and FAT32 file systems, making it impossible for normal FAT file system drivers to mount such volumes.
The non-bootablesuperblock sector is 4 KB in size and holds an 18 byte large BPB-like structure completely different from normalBPBs. Clusters are typically 16 KB in size and there is only one copy of the FAT on the Xbox. Directory entries are 64 bytes in size instead of the normal32 bytes. Files can have filenames up to 42 characters long using theOEM character set and be up to 4 GB minus 1 byte in size. The on-disk timestamps hold creation, modification and access dates and times but differ from FAT: in FAT, theepoch is1980; in FATX, the epoch is2000. On theXbox 360, the epoch is 1980.[60]
exFAT is a file system introduced withWindows Embedded CE 6.0 in November 2006 and brought to the Windows NT family withVista Service Pack 1 andWindows XP Service Pack 3 (or separate installation of Windows XP Update KB955704). It is loosely based on the File Allocation Table architecture, but incompatible, proprietary and protected by patents.[61]
exFAT is intended for use onflash drives andmemory cards such asSDXC andMemory Stick XC, where FAT32 is otherwise used. Vendors usually pre-format SDXC cards with it. Its main benefit is its exceeding of the 4 GB file size limit, as file size references are stored with eight instead of four bytes, increasing the limit to 264 − 1 bytes.
Microsoft'sGUI and command-line format utilities offer it as an alternative toNTFS (and, for smaller partitions, toFAT16B andFAT32). TheMBRpartition type is0x07 (the same as used forIFS,HPFS, and NTFS). Logical geometry information located in theVBR is stored in a format not resembling any kind of BPB.
In early 2010, the file system wasreverse-engineered by theSANS Institute.[62] On August 28, 2019, Microsoft published the technical specification for exFAT so that it can be used in the Linux kernel and other operating systems.[63]
Microsoft applied for, and was granted, a series of patents for key parts of the FAT file system in the mid-1990s. All four pertain to long-filename extensions to FAT first seen inWindows 95: U.S. patent 5,579,517,[64] U.S. patent 5,745,902,[65] U.S. patent 5,758,352,[66] U.S. patent 6,286,013 (all expired since 2013).[67]
On December 3, 2003, Microsoft announced[68] that it would be offering licenses for use of its FAT specification and "associated intellectual property", at the cost of aUS$0.25 royalty per unit sold, with aUS$250,000 maximum royalty per license agreement.[69] To this end, Microsoft cited four patents on the FAT file system as the basis of its intellectual property claims.
In the EFI FAT32 specification,[9] Microsoft specifically grants a number of rights, which many readers have interpreted as permitting operating system vendors to implement FAT.[70] Non-Microsoft patents affecting FAT include: U.S. patent 5,367,671, specific to theOS/2 extended object attributes (expired in 2011).[71]
ThePublic Patent Foundation (PUBPAT) submitted evidence to theUS Patent and Trademark Office (USPTO) in 2004 disputing the validity of U.S. patent 5,579,517,[64] including prior art references fromXerox and IBM.[72] The USPTO opened an investigation and concluded by rejecting all claims in the patent.[73] The next year, the USPTO further announced that following the re-examination process, it affirmed the rejection of '517 and additionally found U.S. patent 5,758,352[66] invalid on the grounds that the patent had incorrect assignees.
However, in 2006, the USPTO ruled that features of Microsoft's implementation of the FAT system were "novel and non-obvious", reversing both earlier decisions and leaving the patents valid.[74]
In February 2009, Microsoft filed apatent infringement lawsuit againstTomTom alleging that the device maker's products infringe on patents related toVFAT long filenames. As some TomTom products are based onLinux, this marked the first time that Microsoft tried to enforce its patents against the Linux platform.[75] The lawsuit was settled out of court the following month with an agreement that Microsoft be given access to four of TomTom's patents, that TomTom will drop support for the VFAT long filenames from its products, and that in return Microsoft not seek legal action against TomTom for the five-year duration of the settlement agreement.[76]
In October 2010, Microsoft filed a patent infringement lawsuit againstMotorola alleging several patents (including two of the VFAT patents) were not licensed for use in theAndroid operating system.[77] They also submitted a complaint to theITC.[78]Developers of open source software have designed methods intended to circumvent Microsoft's patents.[79][80]
In 2013, patent EP0618540 "common name space for long and short filenames" (expired since 2014[81]) was invalidated in Germany.[82] After the appeal was withdrawn, this judgment became final on the 28th October 2015.[83]
ACCDATE=drive1+|- [drive2+|-]..."... only 2^12 (that is, 4096) allocation units or clusters can be addressed. In fact, the number is less than this, since 000h and 001h are not used and FF0h to FFFh are reserved or used for other purposes, leaving 002h to FEFh (2 to 4079) as the range of possible clusters.
The numbering starts with 2; the first two numbers, 0 and 1, are reserved.
Clusters cannot be 64 kilobytes (KB) or larger
0x00 for a file that hasEAs these EAs will no longer be found using DosFindFirst/Next calls only. The otherOS/2 calls for retrieving EAs (DosQueryPathInfo, DosQueryFileInfo and DosEnumAttribute) do not rely on this byte. Also the opposite could [...] occur. [...] In this situation only the performance of directory scans will be decreased. Both situations [...] are corrected byCHKDSK".0xEA and0xEC magic values.{{cite web}}: CS1 maint: bot: original URL status unknown (link)Standards ofEcma International | ||
|---|---|---|
| Application interfaces |  | |
| File systems (tape) | ||
| File systems (disk) | ||
| Graphics | ||
| Programming languages | ||
| Radio link interfaces | ||
| Other | ||
List of Ecma standards (1961 – present) | ||
International Organization for Standardization (ISO) standards | |
|---|---|
| 1–9999 |
|
| 10000–19999 |
|
| 20000–29999 | |
| 30000+ | |
