A FAT file system is a specific type of computer
file system
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
architecture and a family of industry-standard file systems utilizing it.
The FAT file system is a legacy file system which is simple and robust.
It offers good performance even in very light-weight implementations, but cannot deliver the same performance, reliability and scalability as some modern file systems. It is, however, supported for compatibility reasons by nearly all currently developed
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s for
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
s and many
home computers,
mobile device
A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...
s and
embedded system
An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...
s, and thus is a well suited file system for data exchange between computers and devices of almost any type and age from 1981 through the present.
Originally designed in 1977 for use on
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
s, FAT was soon adapted and used almost universally on
hard disks
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magneti ...
throughout the
DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicatio ...
and
Windows 9x
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subs ...
eras for two decades. Today, FAT file systems are still commonly found on floppy disks,
USB stick
A USB flash drive (also called a thumb drive) is a data storage device that includes flash memory with an integrated USB interface. It is typically removable, rewritable and much smaller than an optical disc. Most weigh less than . Since first ...
s,
flash
Flash, flashes, or FLASH may refer to:
Arts, entertainment, and media
Fictional aliases
* Flash (DC Comics character), several DC Comics superheroes with super speed:
** Flash (Barry Allen)
** Flash (Jay Garrick)
** Wally West, the first Kid ...
and other
solid-state
Solid state, or solid matter, is one of the four fundamental states of matter.
Solid state may also refer to:
Electronics
* Solid-state electronics, circuits built of solid materials
* Solid state ionics, study of ionic conductors and their use ...
memory card
A memory card is an electronic data storage device used for storing digital information, typically using flash memory. These are commonly used in digital portable electronic devices. They allow adding memory to such devices using a card in a so ...
s and modules, and many portable and embedded devices.
DCF implements FAT as the standard file system for
digital camera
A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile device ...
s since 1998.
FAT is also utilized for the
EFI system partition (partition type ) in the boot stage of
EFI-compliant computers.
For floppy disks, FAT has been standardized as
ECMA-107
and
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
/
IEC
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
9293:1994
(superseding ISO 9293:1987
). These standards cover FAT12 and FAT16 with only short
8.3 filename
An 8.3 filename (also called a short filename or SFN) is a filename convention used by old versions of DOS and versions of Microsoft Windows prior to Windows 95 and Windows NT 3.5. It is also used in modern Microsoft operating systems as an alterna ...
support;
long filename
Long filename (LFN) support is Microsoft's backward-compatible extension of the 8.3 filename (short filename) naming scheme used in DOS. Long filenames can be more descriptive, including longer filename extensions such as .jpeg, .tiff, .html, a ...
s with
VFAT
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...
are
partially patented.
According to Google Patents the status of "Common name space for long and short filenames" (US5758352A) was expired in 2019, which may mean that the patent has expired completely.
Technical overview
The name of the file system originates from the file system's prominent usage of an index table, the ''
File Allocation Table
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
'', statically allocated at the time of formatting. The table contains entries for each ''
cluster
may refer to:
Science and technology Astronomy
* Cluster (spacecraft), constellation of four European Space Agency spacecraft
* Asteroid cluster, a small asteroid family
* Cluster II (spacecraft), a European Space Agency mission to study t ...
'', a contiguous area of disk storage. Each entry contains either the number of the next cluster in the file, or else a marker indicating end of file, unused disk space, or special reserved areas of the disk. The ''root 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 table, 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. In much the same way, ''sub-directories'' are implemented as special files containing the ''directory entries'' of their respective files.
Originally designed as an 8-bit file system, the maximum number of clusters has been significantly increased as disk drives have evolved, and so the number of bits used to identify each cluster has grown. The successive major versions of the FAT format are named after the number of table element bits: 12 (
FAT12
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
), 16 (
FAT16
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on Hard disk drive, hard disks and other devices. It is often supported for compatibi ...
), and 32 (
FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...
). Except for the original
8-bit FAT
In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...
precursor, each of these variants is still in use. The FAT standard has also been expanded in other ways while generally preserving backward compatibility with existing software.
Layout
A FAT file system is composed of four regions:
; Reserved sectors
: The first reserved sector (logical sector 0) is the
Boot Sector (also called ''
Volume Boot Record'' or simply ''VBR''). It includes an area called the ''
BIOS Parameter Block
In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the volume boot record (VBR) describing the physical layout of a data storage volume. On partitioned devices, such as hard disks, the BPB describes the volume ...
'' (''BPB'') which contains some basic file system information, in particular its type and pointers to the location of the other sections, and usually contains the operating system's
boot loader
A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer.
When a computer is turned off, its softwareincluding operating systems, application code, a ...
code.
: Important information from the Boot Sector is accessible through an operating system structure called the ''
Drive Parameter Block'' (''DPB'') in DOS and OS/2.
: The total count of reserved sectors is indicated by a field inside the Boot Sector, and is usually 32 on FAT32 file systems.
: For FAT32 file systems, the reserved sectors include a ''
File System Information Sector'' at logical sector 1 and a ''Backup Boot Sector'' at logical sector 6.
: While many other vendors have continued to utilize a single-sector setup (logical sector 0 only) for the bootstrap loader, Microsoft's boot sector code has grown to span over logical sectors 0 and 2 since the introduction of FAT32, with logical sector 0 depending on sub-routines in logical sector 2. The Backup Boot Sector area consists of three logical sectors 6, 7, and 8 as well. In some cases, Microsoft also uses sector 12 of the reserved sectors area for an extended boot loader.
; FAT Region
: This typically contains two copies of the ''
File Allocation Table
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
'' for the sake of redundancy checking, although rarely used, even by disk repair utilities.
: These are maps of the Data Region, indicating which clusters are used by files and directories. In FAT12 and FAT16 they immediately follow the reserved sectors.
: Typically the extra copies are kept in tight synchronization on writes, and on reads they are only used when errors occur in the first FAT.
: The first two clusters (cluster
0 and
1) in the map contain special values.
; Root Directory Region
: This is a ''
Directory Table'' that stores information about the files and directories located in the root directory. It is only used with FAT12 and FAT16, and imposes on the root directory a fixed maximum size which is pre-allocated at creation of this volume. FAT32 stores the root directory in the Data Region, along with files and other directories, allowing it to grow without such a constraint. Thus, for FAT32, the Data Region starts here.
; Data Region
: This is where the actual file and directory data is stored and takes up most of the partition. Traditionally, the unused parts of the data region are initialized with a filler value of as per the INT 1Eh's
Disk Parameter Table
Disk or disc may refer to:
* Disk (mathematics), a geometric shape
* Disk storage
Music
* Disc (band), an American experimental music band
* ''Disk'' (album), a 1995 EP by Moby
Other uses
* Disk (functional analysis), a subset of a vector sp ...
(DPT) during format on IBM compatible machines, but also used on the
Atari Portfolio
The Atari Portfolio (Atari PC Folio) is an IBM PC-compatible palmtop PC, released by Atari Corporation in June 1989. This makes it the world's first palmtop computer. . 8-inch CP/M floppies typically came pre-formatted with a value of ;
by way of Digital Research
this value was also used on
Atari ST
The Atari ST is a line of personal computers from Atari Corporation and the successor to the Atari 8-bit family. The initial model, the Atari 520ST, had limited release in April–June 1985 and was widely available in July. It was the first pers ...
formatted floppies.
Amstrad
Amstrad was a British electronics company, founded in 1968 by Alan Sugar at the age of 21. The name is a contraction of Alan Michael Sugar Trading. It was first listed on the London Stock Exchange in April 1980. During the late 1980s, Amstrad ...
used instead. Some modern formatters wipe hard disks with a value of , whereas a value of , the default value of a non-programmed flash block, is used on flash memory to reduce
wear
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology.
Wear in m ...
. The latter value is typically also used on ROM disks. (Some advanced formatting tools allow to configure the format filler byte.
)
: The size of files and subdirectories can be increased arbitrarily (as long as there are free clusters) by simply adding more links to the file's chain in the FAT. Files are allocated in units of clusters, so if a file resides in a cluster, are wasted.
: FAT32 typically commences the Root Directory Table in cluster number 2: the first cluster of the Data Region.
FAT uses
little-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most si ...
format for all entries in the header (except for, where explicitly mentioned, for some entries on Atari ST boot sectors) and the FAT(s).
It is possible to allocate more FAT sectors than necessary for the number of clusters. The end of the last sector of each FAT copy can be unused if there are no corresponding clusters. The total number of sectors (as noted in the boot record) can be larger than the number of sectors used by data (clusters × sectors per cluster), FATs (number of FATs × sectors per FAT), the root directory (n/a for FAT32), and hidden sectors including the boot sector: this would result in unused sectors at the end of the volume. If a partition contains more sectors than the total number of sectors occupied by the file system it would also result in unused sectors, at the end of the partition, after the volume.
Reserved sectors area
Boot Sector
On non-partitioned
storage devices, such as
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
s, the
Boot Sector (
VBR) is the first sector (logical sector 0 with physical CHS address 0/0/1 or LBA address 0). For partitioned storage devices such as hard disks, the Boot Sector is the first sector of a partition, as specified in the partition table of the device.
Common structure of the Boot Sector used by most FAT versions for IBM compatible x86 machines since DOS 2.0 are:
FAT-formatted
Atari ST
The Atari ST is a line of personal computers from Atari Corporation and the successor to the Atari 8-bit family. The initial model, the Atari 520ST, had limited release in April–June 1985 and was widely available in July. It was the first pers ...
floppies have a very similar boot sector layout:
FAT12-formatted
MSX-DOS
MSX-DOS is a discontinued disk operating system developed by Microsoft for the 8-bit home computer standard MSX, and is a cross between MS-DOS 1.25 and CP/M-80 2.
MSX-DOS
MSX-DOS and the extended BASIC with 3½-inch floppy disk support ...
volumes have a very similar boot sector layout:
BIOS Parameter Block
Common structure of the first 25 bytes of the
BIOS Parameter Block
In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the volume boot record (VBR) describing the physical layout of a data storage volume. On partitioned devices, such as hard disks, the BPB describes the volume ...
(BPB) used by FAT versions since DOS 2.0 (bytes at sector offset to are stored since DOS 2.0, but not always used before DOS 3.2, values at to are used since DOS 3.0):
DOS 3.0 BPB:
The following extensions were documented since DOS 3.0, however, they were already supported by some issues of DOS 2.11.
MS-DOS 3.10 still supported the DOS 2.0 format, but could use the DOS 3.0 format as well.
DOS 3.2 BPB:
Officially, MS-DOS 3.20 still used the DOS 3.0 format, but
SYS
and
FORMAT
Format may refer to:
Printing and visual media
* Text formatting, the typesetting of text elements
* Paper formats, or paper size standards
* Newspaper format, the size of the paper page
Computing
* File format, particular way that informatio ...
were adapted to support a 6 bytes longer format already (of which not all entries were used).
DOS 3.31 BPB:
Officially introduced with DOS 3.31 and not used by DOS 3.2, some DOS 3.2 utilities were designed to be aware of this new format already. Official documentation recommends to trust these values only if the logical sectors entry at offset is zero.
A simple formula translates a volume's given cluster number
CN
to a logical sector number
LSN
:
# Determine (once)
SSA=RSC+FN×SF+ceil((32×RDE)/SS)
, where the reserved sector count
RSC
is stored at offset , the number of FATs
FN
at offset , the sectors per FAT
SF
at offset (FAT12/FAT16) or (FAT32), the root directory entries
RDE
at offset , the sector size
SS
at offset , and
ceil(x)
rounds up to a whole number.
# Determine
LSN=SSA+(CN−2)×SC
, where the sectors per cluster
SC
are stored at offset .
On unpartitioned media the volume's number of hidden sectors is zero and therefore
LSN
and
LBA
addresses become the same for as long as a volume's logical sector size is identical to the underlying medium's physical sector size. Under these conditions, it is also simple to translate between
CHS
addresses and
LSNs
as well:
LSN=SPT×(HN+(NOS×TN))+SN−1
, where the sectors per track
SPT
are stored at offset , and the number of sides
NOS
at offset . Track number
TN
, head number
HN
, and sector number
SN
correspond to
Cylinder-head-sector
Cylinder-head-sector (CHS) is an early method for giving addresses to each physical block of data on a hard disk drive.
It is a 3D-coordinate system made out of a vertical coordinate ''head'', a horizontal (or radial) coordinate ''cylinder'', an ...
: the formula gives the known CHS to
LBA translation.
Extended BIOS Parameter Block
Further structure used by FAT12 and FAT16 since OS/2 1.0 and DOS 4.0, also known as
Extended BIOS Parameter Block
In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the volume boot record (VBR) describing the physical layout of a Computer data storage, data storage Volume (computing), volume. On partitioned devices, such a ...
(EBPB) (bytes below sector offset are the same as for the DOS 3.31 BPB):
FAT32 Extended BIOS Parameter Block
In essence FAT32 inserts 28 bytes into the EBPB, followed by the remaining 26 (or sometimes only 7)
EBPB bytes as shown above for FAT12 and FAT16. Microsoft and IBM operating systems determine the type of FAT file system used on a volume solely by the number of clusters, not by the used BPB format or the indicated file system type, that is, it is technically possible to use a "FAT32 EBPB" also for FAT12 and FAT16 volumes as well as a DOS 4.0 EBPB for small FAT32 volumes. Since such volumes were found to be created by Windows operating systems under some odd conditions,
operating systems should be prepared to cope with these hybrid forms.
Exceptions
Versions of DOS before 3.2 totally or partially relied on the
media descriptor byte in the BPB or the
FAT ID
A FAT file system is a specific type of computer file system architecture and a family of industry-standard file systems utilizing it.
The FAT file system is a legacy file system which is simple and robust. It offers good performance even in ...
byte in cluster 0 of the first FAT in order to determine FAT12 diskette formats even if a BPB is present. Depending on the FAT ID found and the drive type detected they default to use one of the following BPB prototypes instead of using the values actually stored in the BPB.
Originally, the FAT ID was meant to be a bit flag with all bits set except for bit 2 cleared to indicate an 80 track (vs. 40 track) format, bit 1 cleared to indicate a 9 sector (vs. 8 sector) format, and bit 0 cleared to indicate a single-sided (vs. double-sided) format,
but this scheme was not followed by all OEMs and became obsolete with the introduction of hard disks and high-density formats. Also, the various 8-inch formats supported by
86-DOS
86-DOS (known internally as QDOS, for Quick and Dirty Operating System) is a discontinued operating system developed and marketed by Seattle Computer Products (SCP) for its Intel 8086-based computer kit.
86-DOS shared a few of its commands wit ...
and MS-DOS do not fit this scheme.
Microsoft recommends to distinguish between the two 8-inch formats for FAT ID by trying to read of a single-density address mark. If this results in an error, the medium must be double-density.
The table does not list a number of incompatible 8-inch and 5.25-inch
FAT12 floppy formats supported by 86-DOS, which differ either in the size of the directory entries (16 bytes vs. 32 bytes) or in the extent of the reserved sectors area (several whole tracks vs. one logical sector only).
The implementation of a single-sided 315 KB FAT12 format used in
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
for the
Apricot PC
The Apricot PC (originally called the ''ACT Apricot'') is a personal computer produced by Apricot Computers, then still known as Applied Computer Techniques or ACT. Released in late 1983, it was ACT's first independently developed microcomputer, f ...
and
F1e had a different boot sector layout, to accommodate that computer's non-IBM compatible BIOS. The jump instruction and OEM name were omitted, and the MS-DOS BPB parameters (offsets - in the standard boot sector) were located at offset . The
Portable
Portable may refer to:
General
* Portable building, a manufactured structure that is built off site and moved in upon completion of site and utility work
* Portable classroom, a temporary building installed on the grounds of a school to provide a ...
,
F1,
PC duo and
Xi FD supported a non-standard double-sided 720 KB FAT12 format instead.
The differences in the boot sector layout and media IDs made these formats incompatible with many other operating systems. The geometry parameters for these formats are:
* 315 KB: Bytes per logical sector: 512 bytes, logical sectors per cluster: 1, reserved logical sectors: 1, number of FATs: 2, root directory entries: 128, total logical sectors: 630, FAT ID: , logical sectors per FAT: 2, physical sectors per track: 9, number of heads: 1.
* 720 KB: Bytes per logical sector: 512 bytes, logical sectors per cluster: 2, reserved logical sectors: 1, number of FATs: 2, root directory entries: 176, total logical sectors: 1440, FAT ID: , logical sectors per FAT: 3, physical sectors per track: 9, number of heads: 2.
Later versions of
Apricot MS-DOS gained the ability to read and write disks with the standard boot sector in addition to those with the Apricot one. These formats were also supported by
DOS Plus
DOS Plus (erroneously also known as DOS+) was the first operating system developed by Digital Research's OEM Support Group in Newbury, Berkshire, UK, first released in 1985. DOS Plus 1.0 was based on CP/M-86 Plus combined with the PCMODE e ...
2.1e/g for the Apricot ACT series.
The DOS Plus adaptation for the
BBC Master 512
The BBC Master is a home computer released by Acorn Computers in early 1986. It was designed and built for the BBC, British Broadcasting Corporation (BBC) and was the successor to the BBC Micro, BBC Micro Model B. The Master 128 remained in produ ...
supported two FAT12 formats on 80-track, double-sided, double-density 5.25" drives, which did not use conventional boot sectors at all. 800 KB data disks omitted a boot sector and began with a single copy of the FAT.
The first byte of the relocated FAT in logical sector 0 was used to determine the disk's capacity. 640 KB boot disks began with a miniature
ADFS file system containing the boot loader, followed by a single FAT.
Also, the 640 KB format differed by using physical CHS sector numbers starting with 0 (not 1, as common) and incrementing sectors in the order sector-track-head (not sector-head-track, as common).
The FAT started at the beginning of the next track. These differences make these formats unrecognizable by other operating systems. The geometry parameters for these formats are:
* 800 KB: Bytes per logical sector: 1024 bytes, logical sectors per cluster: 1, reserved logical sectors: 0, number of FATs: 1, root directory entries: 192, total logical sectors: 800, FAT ID: , logical sectors per FAT: 2, physical sectors per track: 5, number of heads: 2.
* 640 KB: Bytes per logical sector: 256 bytes, logical sectors per cluster: 8, reserved logical sectors: 16, number of FATs: 1, root directory entries: 112, total logical sectors: 2560, FAT ID: , logical sectors per FAT: 2, physical sectors per track: 16, number of heads: 2.
DOS Plus for the Master 512 could also access standard PC disks formatted to or , using the first byte of the FAT in logical sector 1 to determine the capacity.
The DEC Rainbow 100 (all variations) supported one FAT12 format on 80-track, single-sided, quad-density 5.25" drives. The first two tracks were reserved for the boot loader, but didn't contain an MBR nor a BPB (MS-DOS used a static in-memory BPB instead). The boot sector (track 0, side 0, sector 1) was Z80 code beginning with DI . The 8088 bootstrap was loaded by the Z80. Track 1, side 0, sector 2 starts with the Media/FAT ID byte . Unformatted disks use instead. The file system starts on track 2, side 0, sector 1. There are 2 copies of the FAT and 96 entries in the root directory. In addition, there is a physical to logical track mapping to effect a 2:1 sector interleaving. The disks were formatted with the physical sectors in order numbered 1 to 10 on each track after the reserved tracks, but the logical sectors from 1 to 10 were stored in physical sectors 1, 6, 2, 7, 3, 8, 4, 9, 5, 10.
FS Information Sector
The "FS Information Sector" was introduced in FAT32
for speeding up access times of certain operations (in particular, getting the amount of free space). It is located at a logical sector number specified in the FAT32 EBPB boot record at position (usually logical sector 1, immediately after the boot record itself).
The sector's data may be outdated and not reflect the current media contents, because not all operating systems update or use this sector, and even if they do, the contents is not valid when the medium has been ejected without properly unmounting the volume or after a power-failure. Therefore, operating systems should first inspect a volume's optional shutdown status bitflags residing in the FAT entry of
cluster 1 or the FAT32 EBPB at offset and ignore the data stored in the FS information sector, if these bitflags indicate that the volume was not properly unmounted before. This does not cause any problems other than a possible speed penalty for the first free space query or data cluster allocation; see
fragmentation.
If this sector is present on a FAT32 volume, the minimum allowed
logical sector size is 512 bytes, whereas otherwise it would be 128 bytes. Some FAT32 implementations support a slight variation of Microsoft's specification by making the FS information sector optional by specifying a value of
(or ) in the entry at offset .
File Allocation Table
Cluster map
A volume's data area is divided into identically sized ''clusters''—small blocks of contiguous space. Cluster sizes vary depending on the type of FAT file system being used and the size of the drive; typical cluster sizes range from 2 to .
Each file may occupy one or more clusters depending on its size. Thus, a file is represented by a chain of clusters (referred to as a
singly linked list
In computer science, a linked list is a linear collection of data elements whose order is not given by their physical placement in memory. Instead, each element points to the next. It is a data structure consisting of a collection of nodes whic ...
). These clusters are not necessarily stored adjacent to one another on the disk's surface but are often instead ''fragmented'' throughout the Data Region.
Each version of the FAT file system uses a different size for FAT entries. Smaller numbers result in a smaller FAT, but waste space in large partitions by needing to allocate in large clusters.
The
FAT12
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
file system uses 12 bits per FAT entry, thus two entries span 3 bytes. It is consistently
little-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most si ...
: if those three bytes are considered as one little-endian 24-bit number, the 12 least significant bits represent the first entry (e.g. cluster 0) and the 12 most significant bits the second (e.g. cluster 1). In other words, while the low eight bits of the first cluster in the row are stored in the first byte, the top four bits are stored in the low nibble of the second byte, whereas the low four bits of the subsequent cluster in the row are stored in the high nibble of the second byte and its higher eight bits in the third byte.
The
FAT16
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on Hard disk drive, hard disks and other devices. It is often supported for compatibi ...
file system uses 16 bits per FAT entry, thus one entry spans two bytes in little-endian byte order:
The
FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...
file system uses 32 bits per FAT entry, thus one entry spans four bytes in little-endian byte order. The four top bits of each entry are reserved for other purposes; they are cleared during formatting and should not be changed otherwise. They must be masked off before interpreting the entry as 28-bit cluster address.
The ''File Allocation Table'' (''FAT'') is a contiguous number of sectors immediately following the area of reserved sectors. It represents a list of entries that map to each cluster on the volume. Each entry records one of five things:
* the cluster number of the next cluster in a chain
* a special ''end of cluster-chain'' (''EOC'') entry that indicates the end of a chain
* a special entry to mark a bad cluster
* a zero to note that the cluster is unused
For very early versions of DOS to recognize the file system, the system must have been booted from the volume or the volume's FAT must start with the volume's second sector (logical sector 1 with physical CHS address 0/0/2 or LBA address 1), that is, immediately following the boot sector. Operating systems assume this hard-wired location of the FAT in order to find the
FAT ID
A FAT file system is a specific type of computer file system architecture and a family of industry-standard file systems utilizing it.
The FAT file system is a legacy file system which is simple and robust. It offers good performance even in ...
in the FAT's cluster 0 entry on DOS 1.0-1.1 FAT diskettes, where no valid BPB is found.
Special entries
The first two entries in a FAT store special values:
The first entry (cluster 0 in the FAT) holds the FAT ID since
MS-DOS 1.20
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few oper ...
and
PC DOS 1.1 (allowed values - with - reserved) in bits 7-0, which is also copied into the BPB of the boot sector, offset since DOS 2.0. The remaining 4 bits (if FAT12), 8 bits (if FAT16) or 20 bits (if FAT32) of this entry are always 1. These values were arranged so that the entry would also function as an "trap-all" end-of-chain marker for all data clusters holding a value of zero. Additionally, for FAT IDs other than (and ) it is possible to determine the correct nibble and byte order (to be) used by the file system driver, however, the FAT file system officially uses a
little-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most si ...
representation only and there are no known implementations of variants using
big-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...
values instead.
86-DOS 0.42
86-DOS (known internally as QDOS, for Quick and Dirty Operating System) is a discontinued operating system developed and marketed by Seattle Computer Products (SCP) for its Intel 8086-based computer kit.
86-DOS shared a few of its commands w ...
up to
MS-DOS 1.14 used hard-wired drive profiles instead of a FAT ID, but used this byte to distinguish between media formatted with 32-byte or 16-byte directory entries, as they were used prior to 86-DOS 0.42.
The second entry (cluster 1 in the FAT) nominally stores the end-of-cluster-chain marker as used by the formater, but typically always holds / / , that is, with the exception of bits 31-28 on FAT32 volumes these bits are normally always set. Some Microsoft operating systems, however, set these bits if the volume is not the volume holding the running operating system (that is, use instead of here).
(In conjunction with alternative end-of-chain markers the lowest bits 2-0 can become zero for the lowest allowed end-of-chain marker / / ; bit 3 should be reserved as well given that clusters / / and higher are officially reserved. Some operating systems may not be able to mount some volumes if any of these bits are not set, therefore the default end-of-chain marker should not be changed.) For DOS 1 and 2, the entry was documented as reserved for future use.
Since DOS 7.1 the two most-significant bits of this cluster entry may hold two optional bitflags representing the current volume status on FAT16 and FAT32, but not on FAT12 volumes. These bitflags are not supported by all operating systems, but operating systems supporting this feature would set these bits on shutdown and clear the most significant bit on startup:
If bit 15 (on FAT16) or bit 27 (on FAT32)
is not set when mounting the volume, the volume was not properly unmounted before shutdown or ejection and thus is in an unknown and possibly "dirty" state.
On FAT32 volumes, the
FS Information Sector may hold outdated data and thus should not be used. The operating system would then typically run
SCANDISK or
CHKDSK
In computing, CHKDSK (short for "check disk") is a system tool and command in DOS, Digital Research FlexOS, IBM/Toshiba 4690 OS, IBM OS/2, Microsoft Windows and related operating systems. It verifies the file system integrity of a volume and at ...
on the next startup
(but not on insertion of removable media) to ensure and possibly reestablish the volume's integrity.
If bit 14 (on FAT16) or bit 26 (on FAT32)
is cleared, the operating system has encountered disk I/O errors on startup,
a possible indication for bad sectors. Operating systems aware of this extension will interpret this as a recommendation to carry out a surface scan (
SCANDISK) on the next boot.
(A similar set of bitflags exists in the FAT12/FAT16 EBPB at offset or the FAT32 EBPB at offset . While the cluster 1 entry can be accessed by file system drivers once they have mounted the volume, the EBPB entry is available even when the volume is not mounted and thus easier to use by disk block device drivers or partitioning tools.)
If the number of FATs in the BPB is not set to 2, the second cluster entry in the first FAT (cluster 1) may also reflect the status of a
TFAT Transaction-Safe FAT File System (TFAT) and Transaction-Safe Extended FAT File System (TexFAT) refer to two file systems used in Microsoft products to provide transaction-safety for data stored on a disk. The goal is to reduce the risk of data loss ...
volume for TFAT-aware operating systems. If the cluster 1 entry in that FAT holds the value 0, this may indicate that the second FAT represents the last known valid transaction state and should be copied over the first FAT, whereas the first FAT should be copied over the second FAT if all bits are set.
Some non-standard FAT12/FAT16 implementations utilize the cluster 1 entry to store the starting cluster of a variable-sized root directory (typically 2
). This may occur when the
number of root directory entries in the BPB holds a value of 0 and no FAT32 EBPB is found (no signature or at offset ).
This extension, however, is not supported by mainstream operating systems,
as it conflicts with other possible uses of the cluster 1 entry. Most conflicts can be ruled out if this extension is only allowed for FAT12 with less than and FAT16 volumes with less than clusters and 2 FATs.
Because these first two FAT entries store special values, there are no data clusters 0 or 1. The first data cluster (after the root directory if FAT12/FAT16) is cluster 2,
marking the beginning of the data area.
Cluster values
FAT entry values:
FAT32 uses 28 bits for cluster numbers. The remaining 4 bits in the 32-bit FAT entry are usually zero, but are reserved and should be left untouched. A standard conformant FAT32 file system driver or maintenance tool must not rely on the upper 4 bits to be zero and it must strip them off before evaluating the cluster number in order to cope with possible future expansions where these bits may be used for other purposes. They must not be cleared by the file system driver when allocating new clusters, but should be cleared during a reformat.
Size limits
The FAT12, FAT16, FAT16B, and FAT32 variants of the FAT file systems have clear limits based on the number of clusters and the number of sectors per cluster (1, 2, 4, ..., 128). For the typical value of 512 bytes per sector:
FAT12 requirements : 3 sectors on each copy of FAT for every 1,024 clusters
FAT16 requirements : 1 sector on each copy of FAT for every 256 clusters
FAT32 requirements : 1 sector on each copy of FAT for every 128 clusters
FAT12 range : 1 to 4,084 clusters : 1 to 12 sectors per copy of FAT
FAT16 range : 4,085 to 65,524 clusters : 16 to 256 sectors per copy of FAT
FAT32 range : 65,525 to 268,435,444 clusters : 512 to 2,097,152 sectors per copy of FAT
FAT12 minimum : 1 sector per cluster × 1 clusters = 512 bytes (0.5 KiB)
FAT16 minimum : 1 sector per cluster × 4,085 clusters = 2,091,520 bytes (2,042.5 KB)
FAT32 minimum : 1 sector per cluster × 65,525 clusters = 33,548,800 bytes (32,762.5 KB)
FAT12 maximum : 64 sectors per cluster × 4,084 clusters = 133,824,512 bytes (≈ 127 MB)
AT12 maximum : 128 sectors per cluster × 4,084 clusters = 267,694,024 bytes (≈ 255 MB)
FAT16 maximum : 64 sectors per cluster × 65,524 clusters = 2,147,090,432 bytes (≈2,047 MB)
AT16 maximum : 128 sectors per cluster × 65,524 clusters = 4,294,180,864 bytes (≈4,095 MB)
FAT32 maximum : 8 sectors per cluster × 268,435,444 clusters = 1,099,511,578,624 bytes (≈1,024 GB)
FAT32 maximum : 16 sectors per cluster × 268,173,557 clusters = 2,196,877,778,944 bytes (≈2,046 GB)
AT32 maximum : 32 sectors per cluster × 134,152,181 clusters = 2,197,949,333,504 bytes (≈2,047 GB) AT32 maximum : 64 sectors per cluster × 67,092,469 clusters = 2,198,486,024,192 bytes (≈2,047 GB) AT32 maximum : 128 sectors per cluster × 33,550,325 clusters = 2,198,754,099,200 bytes (≈2,047 GB)
:Legend: 268435444+3 is , because FAT32 version 0 uses only 28 bits in the 32-bit cluster numbers, cluster numbers up to flag bad clusters or the end of a file, cluster number 0 flags a free cluster, and cluster number 1 is not used.
Likewise 65524+3 is for FAT16, and 4084+3 is for FAT12. The number of sectors per cluster is a power of 2 fitting in a single byte, the smallest value is 1 (), the biggest value is 128 (). Lines in square brackets indicate the unusual cluster size 128, and for FAT32 the bigger than necessary cluster sizes 32 or 64.
Because each FAT32 entry occupies 32 bits (4 bytes) the maximal number of clusters (268435444) requires 2097152 FAT sectors for a sector size of 512 bytes. 2097152 is , and storing this value needs more than two bytes. Therefore, FAT32 introduced a new 32-bit value in the FAT32 boot sector immediately following the 32-bit value for the total number of sectors introduced in the FAT16B variant.
The boot record extensions introduced with DOS 4.0 start with a magic 40 () or 41 (). Typically FAT drivers look only at the number of clusters to distinguish FAT12, FAT16, and FAT32: the human readable strings identifying the FAT variant in the boot record are ignored, because they exist only for media formatted with DOS 4.0 or later.
Determining the number of directory entries per cluster is straightforward. Each entry occupies 32 bytes; this results in 16 entries per sector for a sector size of 512 bytes. The DOS 5
RMDIR
In computing, rmdir (or rd) is a command (computing), command which will remove an empty directory (file systems), directory on various operating systems.
Implementations
The command is available in Unix (e.g. macOS, Solaris (operating system), ...
/
RD
command removes the initial "
.
" (this directory) and "
..
" (parent directory) entries in subdirectories directly, therefore sector size 32 on a RAM disk is possible for FAT12, but requires 2 or more sectors per cluster. A FAT12 boot sector without the DOS 4 extensions needs 29 bytes before the first unnecessary FAT16B 32-bit number of hidden sectors, this leaves three bytes for the (on a RAM disk unused) boot code and the magic at the end of all boot sectors. On
Windows NT
Windows NT is a proprietary graphical operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems sc ...
the smallest supported sector size is 128.
On
Windows NT
Windows NT is a proprietary graphical operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems sc ...
operating systems the
FORMAT
command options
/A:128K
and
/A:256K
correspond to the maximal cluster size
0x80
(128) with a sector size 1024 and 2048, respectively. For the common sector size 512
/A:64K
yields 128 sectors per cluster.
Both editions of each ECMA-107
and ISO/IEC 9293
specify a ''Max Cluster Number''
MAX
determined by the formula
MAX=1+trunc((TS-SSA)/SC)
, and reserve cluster numbers
MAX+1
up to 4086 (, FAT12) and later 65526 (, FAT16) for future standardization.
Microsoft's EFI FAT32 specification
states that any FAT file system with less than 4085 clusters is FAT12, else any FAT file system with less than 65,525 clusters is FAT16, and otherwise it is FAT32. The entry for cluster 0 at the beginning of the FAT must be identical to the media descriptor byte found in the BPB, whereas the entry for cluster 1 reflects the end-of-chain value used by the formatter for cluster chains (, or ). The entries for cluster numbers 0 and 1 end at a byte boundary even for FAT12, e.g., for media descriptor .
The first data cluster is 2,
and consequently the last cluster
MAX
gets number
MAX+1
. This results in data cluster numbers 2...4085 () for FAT12, 2...65525 () for FAT16, and 2...268435445 () for FAT32.
The only available values reserved for future standardization are therefore (FAT12) and (FAT16). As noted below "less than 4085" is also used for Linux implementations,
or as
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
's FAT specification puts it:
...when it says <, it does not mean <=. Note also that the numbers are correct. The first number for FAT12 is 4085; the second number for FAT16 is 65525. These numbers and the "<" signs are not wrong.
Fragmentation
The FAT file system does not contain built-in mechanisms which prevent newly written files from becoming scattered across the partition.
On volumes where files are created and deleted frequently or their lengths often changed, the medium will become increasingly fragmented over time.
While the design of the FAT file system does not cause any organizational overhead in disk structures or reduce the amount of free storage space with increased amounts of
fragmentation, as it occurs with
external fragmentation, the time required to read and write fragmented files will increase as the operating system will have to follow the cluster chains in the FAT (with parts having to be loaded into memory first in particular on large volumes) and read the corresponding data physically scattered over the whole medium reducing chances for the low-level block device driver to perform multi-sector disk I/O or initiate larger DMA transfers, thereby effectively increasing I/O protocol overhead as well as arm movement and head settle times inside the disk drive. Also, file operations will become slower with growing fragmentation as it takes increasingly longer for the operating system to find files or free clusters.
Other file systems, e.g.,
HPFS or
exFAT
exFAT (Extensible File Allocation Table) is a file system introduced by Microsoft in 2006 and optimized for flash memory such as USB flash drives and SD cards. exFAT was proprietary until 28 August 2019, when Microsoft published its specificati ...
, use
free space bitmap
Free-space bitmaps are one method used to track allocated sectors by some file systems. While the most simplistic design is highly inefficient, advanced or hybrid implementations of free-space bitmaps are used by some modern file systems.
Exampl ...
s that indicate used and available clusters, which could then be quickly looked up in order to find free contiguous areas. Another solution is the linkage of all free clusters into one or more lists (as is done in
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
file systems). Instead, the FAT has to be scanned as an array to find free clusters, which can lead to performance penalties with large disks.
In fact, seeking for files in large subdirectories or computing the free disk space on FAT volumes is one of the most resource intensive operations, as it requires reading the directory tables or even the entire FAT linearly. Since the total amount of clusters and the size of their entries in the FAT was still small on FAT12 and FAT16 volumes, this could still be tolerated on FAT12 and FAT16 volumes most of the time, considering that the introduction of more sophisticated disk structures would have also increased the complexity and memory footprint of real-mode operating systems with their minimum total memory requirements of 128 KB or less (such as with DOS) for which FAT has been designed and optimized originally.
With the introduction of FAT32, long seek and scan times became more apparent, particularly on very large volumes. A possible justification suggested by Microsoft's
Raymond Chen
Raymond T. Chen (born 1968) is a United States circuit judge of the United States Court of Appeals for the Federal Circuit.
Biography
He joined the intellectual property law firm of Knobbe, Martens, Olson & Bear in Irvine, California. He prosecu ...
for limiting the maximum size of FAT32 partitions created on Windows was the time required to perform a "
DIR
" operation, which always displays the free disk space as the last line.
Displaying this line took longer and longer as the number of clusters increased. FAT32 therefore introduced a special file system information sector where the previously computed amount of free space is preserved over power cycles, so that the free space counter needs to be recalculated only when a removable FAT32 formatted medium gets ejected without first unmounting it or if the system is switched off without properly shutting down the operating system, a problem mostly visible with pre-
ATX
ATX (Advanced Technology eXtended) is a motherboard and power supply configuration specification developed by Intel in 1995 to improve on previous de facto standards like the AT design. It was the first major change in desktop computer enclo ...
-style PCs, on plain DOS systems and some battery-powered consumer products.
With the huge cluster sizes (16 KB, 32 KB, 64 KB) forced by larger FAT partitions,
internal fragmentation
In computer storage, fragmentation is a phenomenon in which storage space, main storage or secondary storage, is used inefficiently, reducing capacity or performance and often both. The exact consequences of fragmentation depend on the specific ...
in form of disk space waste by file slack due to
cluster overhang
In computer storage, fragmentation is a phenomenon in which storage space, main storage or secondary storage, is used inefficiently, reducing capacity or performance and often both. The exact consequences of fragmentation depend on the specifi ...
(as files are rarely exact multiples of cluster size) starts to be a problem as well, especially when there are a great many small files.
Various optimizations and tweaks to the implementation of FAT file system drivers, block device drivers and disk tools have been devised to overcome most of the performance bottlenecks in the file system's inherent design without having to change the layout of the on-disk structures.
They can be divided into on-line and off-line methods and work by trying to avoid fragmentation in the file system in the first place, deploying methods to better cope with existing fragmentation, and by reordering and optimizing the on-disk structures. With optimizations in place, the performance on FAT volumes can often reach that of more sophisticated file systems in practical scenarios, while at the same time retaining the advantage of being accessible even on very small or old systems.
DOS 3.0 and higher will not immediately reuse disk space of deleted files for new allocations but instead seek for previously unused space before starting to use disk space of previously deleted files as well. This not only helps to maintain the integrity of deleted files for as long as possible but also speeds up file allocations and avoids fragmentation, since never before allocated disk space is always unfragmented.
DOS accomplishes this by keeping a pointer to the last allocated cluster on each mounted volume in memory and starts searching for free space from this location upwards instead of at the beginning of the FAT, as it was still done by DOS 2.x.
If the end of the FAT is reached, it would wrap around to continue the search at the beginning of the FAT until either free space has been found or the original position has been reached again without having found free space.
These pointers are initialized to point to the start of the FATs after bootup,
but on FAT32 volumes, DOS 7.1 and higher will attempt to retrieve the last position from the
FS Information Sector.
This mechanism is defeated, however, if an application often deletes and recreates temporary files as the operating system would then try to maintain the integrity of void data effectively causing more fragmentation in the end.
In some DOS versions, the usage of a special API function to create temporary files can be used to avoid this problem.
Additionally, directory entries of deleted files will be marked since DOS 3.0.
DOS 5.0 and higher will start to reuse these entries only when previously unused directory entries have been used up in the table and the system would otherwise have to expand the table itself.
Since DOS 3.3 the operating system provides means to improve the performance of file operations with
FASTOPEN
In computing, FASTOPEN is a DOS terminate-and-stay-resident command, introduced in MS-DOS version 3.3, that provides accelerated access to frequently-used files and directories. The command is also available in SISNE plus.
Overview
The command wo ...
by keeping track of the position of recently opened files or directories in various forms of lists (MS-DOS/PC DOS) or hash tables (DR-DOS), which can reduce file seek and open times significantly. Before DOS 5.0 special care must be taken when using such mechanisms in conjunction with disk defragmentation software bypassing the file system or disk drivers.
Windows NT will allocate disk space to files on FAT in advance, selecting large contiguous areas, but in case of a failure, files which were being appended will appear larger than they were ever written into, with a lot of random data at the end.
Other high-level mechanisms may read in and process larger parts or the complete FAT on startup or on demand when needed and dynamically build up in-memory tree representations of the volume's file structures different from the on-disk structures.
This may, on volumes with many free clusters, occupy even less memory than an image of the FAT itself. In particular on highly fragmented or filled volumes, seeks become much faster than with linear scans over the actual FAT, even if an image of the FAT would be stored in memory. Also, operating on the logically high level of files and cluster-chains instead of on sector or track level, it becomes possible to avoid some degree of file fragmentation in the first place or to carry out local file defragmentation and reordering of directory entries based on their names or access patterns in the background.
Some of the perceived problems with
fragmentation of FAT file systems also result from performance limitations of the underlying block
device driver
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...
s, which becomes more visible the lesser memory is available for sector buffering and track blocking/deblocking:
While the single-tasking DOS had provisions for multi-sector reads and track blocking/deblocking, the operating system and the traditional PC hard disk architecture (
only one outstanding input/output request at a time and
no DMA transfers) originally did not contain mechanisms which could alleviate fragmentation by asynchronously prefetching next data while the application was processing the previous chunks. Such features became available later. Later DOS versions also provided built-in support for look-ahead sector buffering and came with dynamically loadable disk caching programs working on physical or logical sector level, often utilizing
EMS or
XMS memory and sometimes providing adaptive caching strategies or even run in
protected mode
In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as virtual memory, paging and safe multi-tasking d ...
through
DPMS or
Cloaking
Cloaking is a search engine optimization (SEO) technique in which the content presented to the search engine spider is different from that presented to the user's browser. This is done by delivering content based on the IP addresses or the User ...
to increase performance by gaining direct access to the cached data in linear memory rather than through conventional DOS APIs.
Write-behind caching was often not enabled by default with Microsoft software (if present) given the problem of data loss in case of a power failure or crash, made easier by the lack of hardware protection between applications and the system.
Directory table
A ''directory table'' is a special type of file that represents a
directory
Directory may refer to:
* Directory (computing), or folder, a file system structure in which to store computer files
* Directory (OpenVMS command)
* Directory service, a software application for organizing information about a computer network's u ...
(also known as a folder). Since
86-DOS 0.42
86-DOS (known internally as QDOS, for Quick and Dirty Operating System) is a discontinued operating system developed and marketed by Seattle Computer Products (SCP) for its Intel 8086-based computer kit.
86-DOS shared a few of its commands w ...
,
each file or (since MS-DOS 1.40 and PC DOS 2.0) subdirectory stored within it is represented by a 32-byte entry in the table. Each entry records the name, extension, attributes (
archive
An archive is an accumulation of historical records or materials – in any medium – or the physical facility in which they are located.
Archives contain primary source documents that have accumulated over the course of an individual or ...
, directory, hidden, read-only, system and volume), the address of the first cluster of the file/directory's data, the size of the file/directory, and the date
and (since PC DOS 1.1) also the time of last modification. Earlier versions of 86-DOS used 16-byte directory entries only, supporting no files larger than 16 MB and no time of last modification.
Aside from the root directory table in FAT12 and FAT16 file systems, which occupies the special ''Root Directory Region'' location, all directory tables are stored in the data region. The actual number of entries in a directory stored in the data region can grow by adding another cluster to the chain in the FAT.
The FAT file system itself does not impose any limits on the depth of a subdirectory tree for as long as there are free clusters available to allocate the subdirectories, however, the internal Current Directory Structure (CDS) under MS-DOS/PC DOS limits the absolute path of a directory to 66 characters (including the drive letter, but excluding the NUL byte delimiter),
thereby limiting the maximum supported depth of subdirectories to 32, whatever occurs earlier. Concurrent DOS, Multiuser DOS and DR DOS 3.31 to 6.0 (up to including the 1992-11 updates) do not store absolute paths to working directories internally and therefore do not show this limitation.
The same applies to Atari GEMDOS, but the Atari Desktop does not support more than 8 sub-directory levels. Most applications aware of this extension support paths up to at least 127 bytes. FlexOS, 4680 OS and 4690 OS support a length of up to 127 bytes as well, allowing depths down to 60 levels.
PalmDOS, DR DOS 6.0 (since BDOS 7.1) and higher, Novell DOS, and OpenDOS sport a MS-DOS-compatible CDS and therefore have the same length limits as MS-DOS/PC DOS.
Each entry can be preceded by "fake entries" to support a
VFAT long filename
A FAT file system is a specific type of computer file system architecture and a family of industry-standard file systems utilizing it.
The FAT file system is a legacy file system which is simple and robust. It offers good performance even in ...
(LFN); see further below.
Legal characters for DOS short filenames include the following:
* Upper case letters
A
–
Z
* Numbers
0
–
9
* Space (though trailing spaces in either the base name or the extension are considered to be padding and not a part of the file name; also filenames with space in them could not easily be used on the DOS command line prior to Windows 95 because of the lack of a suitable
escaping system). Another exception are the internal commands
MKDIR
The mkdir (make directory) command in the Unix, DOS, DR FlexOS, IBM OS/2, Microsoft Windows, and ReactOS operating systems is used to make a new directory. It is also available in the EFI shell and in the PHP scripting language. In DOS, OS/2, ...
/
MD
and
RMDIR
In computing, rmdir (or rd) is a command (computing), command which will remove an empty directory (file systems), directory on various operating systems.
Implementations
The command is available in Unix (e.g. macOS, Solaris (operating system), ...
/
RD
under DR-DOS which accept single arguments and therefore allow spaces to be entered.
*
! # $ % & ' ( ) - @ ^ _ ` ~
* Characters 128–228
* Characters 230–255
This excludes the following
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
characters:
*
" * / : < > ? \ ,
Windows/MS-DOS has no shell
escape character
In computing and telecommunication, an escape character is a character (computing), character that invokes an alternative interpretation on the following characters in a character sequence. An escape character is a particular case of metacharac ...
*
+ , . ; = /code>
Allowed in long file names only
* Lower case letters a
–z
Stored as A
–Z
; allowed in long file names
* Control characters 0–31
* Character 127 (DEL)
Character 229 () was not allowed as first character in a filename in DOS 1 and 2 due to its use as free entry marker. A special case was added to circumvent this limitation with DOS 3.0 and higher.
The following additional characters are allowed on Atari's GEMDOS, but should be avoided for compatibility with MS-DOS/PC DOS:
* " + , ; < = > ,
The semicolon (;
) should be avoided in filenames under DR DOS 3.31 and higher, PalmDOS, Novell DOS, OpenDOS, Concurrent DOS, Multiuser DOS, System Manager and REAL/32, because it may conflict with the syntax to specify file and directory passwords: "...\DIRSPEC.EXT;DIRPWD\FILESPEC.EXT;FILEPWD
". The operating system will strip off one (and also two—since DR-DOS 7.02) semicolons and pending passwords from the filenames before storing them on disk. (The command processor 4DOS
4DOS is a command-line interpreter by JP Software, designed to replace the default command interpreter COMMAND.COM in Microsoft DOS and Windows. It was written by Rex C. Conn and Tom Rawson and first released in 1989. Compared to the default, ...
uses semicolons for include lists and requires the semicolon to be doubled for password protected files with any commands supporting wildcards.)
The at-sign character (@
) is used for filelists by many DR-DOS, PalmDOS, Novell DOS, OpenDOS and Multiuser DOS, System Manager and REAL/32 commands, as well as by 4DOS and may therefore sometimes be difficult to use in filenames.
Under Multiuser DOS and REAL/32, the exclamation mark (!) is not a valid filename character since it is used to separate multiple commands in a single command line.
Under IBM 4680 OS and 4690 OS, the following characters are not allowed in filenames:
* ? * : . ; , ! + = < > " - / \ ,
Additionally, the following special characters are not allowed in the first, fourth, fifth and eight character of a filename, as they conflict with the host command processor (HCP) and input sequence table build file names:
* @ # ( ) $ &
The DOS file names are in the current OEM character set
Windows code pages are sets of characters or code pages (known as character encodings in other operating systems) used in Microsoft Windows from the 1980s and 1990s. Windows code pages were gradually superseded when Unicode in Microsoft Windows, Un ...
: this can have surprising effects if characters handled in one way for a given code page are interpreted differently for another code page (DOS command CHCP
) with respect to lower and upper case, sorting, or validity as file name character.
Directory entry
Before Microsoft added support for long filenames and creation/access time stamps, bytes – of the directory entry were used by other operating systems to store additional metadata, most notably the operating systems of the Digital Research family stored file passwords, access rights, owner IDs, and file deletion data there. While Microsoft's newer extensions are not fully compatible with these extensions by default, most of them can coexist in third-party FAT implementations (at least on FAT12 and FAT16 volumes).
32-byte directory entries, both in the Root Directory Region and in subdirectories, are of the following format (see also 8.3 filename
An 8.3 filename (also called a short filename or SFN) is a filename convention used by old versions of DOS and versions of Microsoft Windows prior to Windows 95 and Windows NT 3.5. It is also used in modern Microsoft operating systems as an alterna ...
):
The FlexOS
FlexOS is a discontinued modular real-time multiuser computer multitasking, multitasking operating system (RTOS) designed for computer-integrated manufacturing, laboratory, retail and financial markets. Developed by Digital Research's Flexible ...
-based operating systems IBM 4680 OS
FlexOS is a discontinued modular real-time multiuser multitasking operating system (RTOS) designed for computer-integrated manufacturing, laboratory, retail and financial markets. Developed by Digital Research's Flexible Automation Business U ...
and IBM 4690 OS support unique distribution attributes stored in some bits of the previously reserved areas in the directory entries:
# Local: Don't distribute file but keep on local controller only.
# Mirror file on update: Distribute file to server only when file is updated.
# Mirror file on close: Distribute file to server only when file is closed.
# Compound file on update: Distribute file to all controllers when file is updated.
# Compound file on close: Distribute file to all controllers when file is closed.
Some incompatible extensions found in some operating systems include:
VFAT long file names
VFAT
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...
Long File Names (LFNs) are stored on a FAT file system using a trick: adding additional entries into the directory before the normal file entry. The additional entries are marked with the Volume Label, System, Hidden, and Read Only attributes (yielding ), which is a combination that is not expected in the MS-DOS environment, and therefore ignored by MS-DOS programs and third-party utilities. Notably, a directory containing only volume labels is considered as empty and is allowed to be deleted; such a situation appears if files created with long names are deleted from plain DOS. This method is very similar to the DELWATCH method to utilize the volume attribute to hide pending delete files for possible future undeletion since DR DOS 6.0 (1991) and higher. It is also similar to a method publicly discussed to store long filenames on Ataris and under Linux in 1992.
Because older versions of DOS could mistake LFN names in the root directory for the volume label, VFAT was designed to create a blank volume label in the root directory before adding any LFN name entries (if a volume label did not already exist).
Each phony entry can contain up to 13 UCS-2
The Universal Coded Character Set (UCS, Unicode) is a standard set of characters defined by the international standard ISO/IEC 10646, ''Information technology — Universal Coded Character Set (UCS)'' (plus amendments to that standard), whi ...
characters (26 bytes) by using fields in the record which contain file size or time stamps (but not the starting cluster field, for compatibility with disk utilities, the starting cluster field is set to a value of 0. See 8.3 filename
An 8.3 filename (also called a short filename or SFN) is a filename convention used by old versions of DOS and versions of Microsoft Windows prior to Windows 95 and Windows NT 3.5. It is also used in modern Microsoft operating systems as an alterna ...
for additional explanations). Up to 20 of these 13-character entries may be chained, supporting a maximum length of 255 UCS-2 characters.
After the last UCS-2
The Universal Coded Character Set (UCS, Unicode) is a standard set of characters defined by the international standard ISO/IEC 10646, ''Information technology — Universal Coded Character Set (UCS)'' (plus amendments to that standard), whi ...
character, a is added. The remaining unused characters are filled with .
LFN entries use the following format:
If there are multiple LFN entries required to represent a file name, the entry representing the ''end'' of the filename comes first. The sequence number of this entry has bit 6 () set to represent that it is the last logical LFN entry, and it has the highest sequence number. The sequence number decreases in the following entries. The entry representing the ''start'' of the filename has sequence number 1. A value of is used to indicate that the entry is deleted.
On FAT12 and FAT16 volumes, testing for the values at to be zero and at to be non-zero can be used to distinguish between VFAT LFNs and pending delete files under DELWATCH.
For example, a filename like "File with very long filename.ext" would be formatted like this:
A checksum
A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...
also allows verification of whether a long file name matches the 8.3 name; such a mismatch could occur if a file was deleted and re-created using DOS in the same directory position. The checksum is calculated using the algorithm below. (pFCBName is a pointer to the name as it appears in a regular directory entry, i.e. the first eight characters are the filename, and the last three are the extension. The dot is implicit. Any unused space in the filename is padded with space characters (ASCII ). For example, "Readme.txt" would be "README␠␠TXT
".)
unsigned char lfn_checksum(const unsigned char *pFCBName)
If a filename contains only lowercase letters, or is a combination of a lowercase ''basename'' with an uppercase ''extension'', or vice versa; and has no special characters, and fits within the 8.3 limits, a VFAT entry is not created on Windows NT and later versions of Windows such as XP. Instead, two bits in byte of the directory entry are used to indicate that the filename should be considered as entirely or partially lowercase. Specifically, bit 4 means lowercase ''extension'' and bit 3 lowercase ''basename'', which allows for combinations such as "example.TXT
" or "HELLO.txt
" but not "Mixed.txt
". Few other operating systems support it. This creates a backwards-compatibility problem with older Windows versions (Windows 95 / 98 / 98 SE / ME) that see all-uppercase filenames if this extension has been used, and therefore can change the name of a file when it is transported between operating systems, such as on a USB flash drive. Current 2.6.x versions of Linux will recognize this extension when reading (source: kernel 2.6.18 /fs/fat/dir.c
and fs/vfat/namei.c
); the mount option shortname
determines whether this feature is used when writing.
See also
* Comparison of file systems
The following tables compare general and technical information for a number of file systems.
General information
Limits
Metadata
Features File capabilities
Block capabilities
Note that in addition to the below table, blo ...
* Drive letter assignment
In computer data storage, drive letter assignment is the process of assigning alphabetical identifiers to volumes. Unlike the concept of UNIX mount points, where volumes are named and located arbitrarily in a single hierarchical namespace, driv ...
* exFAT
exFAT (Extensible File Allocation Table) is a file system introduced by Microsoft in 2006 and optimized for flash memory such as USB flash drives and SD cards. exFAT was proprietary until 28 August 2019, when Microsoft published its specificati ...
* Extended Boot Record
An extended boot record (EBR), or extended partition boot record (EPBR), is a descriptor for a logical partition under the common DOS disk drive partitioning system. In that system, when one (and only one) partition record entry in the master boot ...
(EBR)
* FAT filesystem and Linux Linux has several filesystem drivers for the File Allocation Table (FAT) filesystem format. These are commonly known by the names used in the mount (Unix), mount command to invoke particular drivers in the kernel: ', ', and '.
History and support ...
* List of file systems
The following lists identify, characterize, and link to more thorough information on Computer file systems.
Many older operating systems support only their one "native" file system, which does not bear any name apart from the name of the operating ...
* Master Boot Record
A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MBR ...
(MBR)
* Partition type
The partition type (or partition ID) in a partition's entry in the partition table inside a master boot record (MBR) is a byte value intended to specify the file system the partition contains or to flag special access methods used to access thes ...
* Timeline of DOS operating systems
This article presents a timeline of events in the history of 16-bit x86 DOS-family disk operating systems from 1980 to present. Non-x86 operating systems named "DOS" are not part of the scope of this timeline.
Also presented is a timeline of ...
* Transaction-Safe FAT File System Transaction-Safe FAT File System (TFAT) and Transaction-Safe Extended FAT File System (TexFAT) refer to two file systems used in Microsoft products to provide transaction-safety for data stored on a disk. The goal is to reduce the risk of data loss ...
* Turbo FAT
In computing, a NetWare File System (NWFS) is a file system based on a heavily modified version of FAT. It was used in the Novell NetWare operating system. It is the default and only file system for all volumes in versions 2.x through 4.x, and t ...
* Volume Boot Record (VBR)
Notes
[If a volume's dirty shutdown flag is still cleared on startup, the volume was not properly unmounted. This would, for example, cause Windows 98 WIN.COM to start SCANDISK in order to check for and repair potential logical file system errors. If the bad sector flag is cleared, it will force a surface scan to be carried out as well. This can be disabled by setting AUTOSCAN=0 in the PTIONSsection in ]MSDOS.SYS
MSDOS.SYS is a system file in MS-DOS and Windows 9x operating systems.
In versions of MS-DOS from 1.1x through 6.22, the file comprises the MS-DOS kernel and is responsible for file access and program management. MSDOS.SYS is loaded by the DOS BI ...
file.
[This is the reason, why had a special meaning in directory entries.]
[One utility providing an option to specify the desired format filler value for hard disks is DR-DOS' FDISK R2.31 with its optional wipe parameter ]/W:246
. In contrast to other FDISK
In computing, the fdisk command-line utility provides disk-partitioning functions, preparatory to defining file systems. fdisk features in the DOS, DR FlexOS, IBM OS/2, and Microsoft Windows operating systems, and in certain ports of FreeBS ...
utilities, DR-DOS FDISK is not only a partitioning tool, but can also format freshly created partitions as FAT12
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...
, FAT16
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on Hard disk drive, hard disks and other devices. It is often supported for compatibi ...
or FAT32
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...
. This reduces the risk to accidentally format wrong volumes.
[For maximum compatibility with MS-DOS/PC DOS and DR-DOS, operating systems trying to determine a floppy disk's format should test on all mentioned opcode sequences at sector offset in ''addition'' to looking for a valid media descriptor byte at sector offset before assuming the presence of a BPB. Although PC DOS 1.0 floppy disks do not contain a BPB, they start with as well, but do not show a at offset . PC DOS 1.10 floppy disks even start with , although they still do not feature a BPB. In both cases, a test for a valid media descriptor at offset would fail (value instead of valid media descriptors and higher). If these tests fail, DOS checks for the presence of a media descriptor byte in the first byte of the first FAT in the sector following the boot sector (logical sector 1 on FAT12/FAT16 floppies).]
[The signature at offset in boot sectors is , that is at offset and at offset . Since ]little-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most si ...
representation must be assumed in the context of IBM PC
The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...
compatible machines, this can be written as 16-bit word in programs for x86
x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...
processors (note the swapped order), whereas it would have to be written as in programs for other CPU architectures using a big-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...
representation. Since this has been mixed up numerous times in books and even in original Microsoft reference documents, this article uses the offset-based byte-wise on-disk representation to avoid any possible misinterpretation.
[The ]checksum
A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...
entry in Atari
Atari () is a brand name that has been owned by several entities since its inception in 1972. It is currently owned by French publisher Atari SA through a subsidiary named Atari Interactive. The original Atari, Inc. (1972–1992), Atari, Inc., ...
boot sectors holds the alignment value, not the magic value itself. The magic value is not stored anywhere on disk. In contrast to Intel x86
x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...
processors, the Motorola 680x0
The Motorola 68000 series (also known as 680x0, m68000, m68k, or 68k) is a family of 32-bit complex instruction set computer (CISC) microprocessors. During the 1980s and early 1990s, they were popular in personal computers and workstations and w ...
processors as used in Atari machines use a big-endian
In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...
memory representation and therefore a big-endian representation must be assumed when calculating the checksum. As a consequence of this, for checksum verification code running on x86 machines, pairs of bytes must be swapped before the 16-bit addition.
[DR-DOS is able to boot off FAT12/FAT16 logical sectored media with logical sector sizes up to 1024 bytes.]
[See other links for special precautions in regard to occurrences of a cluster value of on FAT12 volumes under MS-DOS/PC DOS 3.3 and higher.]
[To avoid potential misinterpretation of directory volume labels with VFAT LFN entries by non-VFAT aware operating systems, the DR-DOS 7.07 FDISK and FORMAT tools are known to explicitly write dummy "]NO␠NAME␠␠␠␠
" directory volume labels if the user skips entering a volume label. The operating system would internally default to return the same string if no directory volume label could be found in the root of a volume, but without a real volume label stored as the first entry (after the directory entries), older operating systems could erroneously pick up VFAT LFN entries instead.
[This ]IBM 4680 OS
FlexOS is a discontinued modular real-time multiuser multitasking operating system (RTOS) designed for computer-integrated manufacturing, laboratory, retail and financial markets. Developed by Digital Research's Flexible Automation Business U ...
and 4690 OS
4690 Operating System (sometimes shortened to 4690 OS or 4690) is a specially designed point of sale (POS) operating system, originally sold by IBM. In 2012, IBM sold its retail business, including this product, to Toshiba, which assumed support. ...
distribution attribute type must have an on-disk bit value of 0 as files fall back to this type when attributes get lost accidentally.
[In order to support the coexistence of DR-DOS with PC DOS and multiple parallel installations of DR-DOS, the extension of the default "]IBMBIO␠␠COM
" boot file name can be changed using the SYS /DR:ext
option, where ext represents the new extension. Other potential DR-DOS boot file names to be expected in special scenarios are "DRBIOS␠␠SYS
", "DRDOS␠␠␠SYS
", "IO␠␠␠␠␠␠SYS
", "JO␠␠␠␠␠␠SYS
".
[The following DOS functions return these register values:
INT 21h/AH=2Ah "Get system date" returned values: CX = year (]1980
Events January
* January 4 – U.S. President Jimmy Carter proclaims a grain embargo against the USSR with the support of the European Commission.
* January 6 – Global Positioning System time epoch begins at 00:00 UTC.
* January 9 – ...
..2099
In contemporary history, the third millennium of the anno Domini or Common Era in the Gregorian calendar is the current millennium spanning the years 2001 to 3000 (21st century, 21st to 30th century, 30th centuries). Ongoing futures studies se ...
), DH = month (1..12), DL = day (1..31).
INT 21h/AH=2Ch "Get system time" returned values: CH = hour (0..23), CL = minute (0..59), DH = second (0..59), DL = 1/100 seconds (0..99).
[Windows XP has been observed to create such hybrid disks when reformatting FAT16B formatted ZIP-100 disks to FAT32 format. The resulting volumes were FAT32 by format, but still used the FAT16B EBPB. (It is unclear how Windows determines the location of the root directory on FAT32 volumes, if only a FAT16 EBPB was used.)]
[Some versions of ]FORMAT
Format may refer to:
Printing and visual media
* Text formatting, the typesetting of text elements
* Paper formats, or paper size standards
* Newspaper format, the size of the paper page
Computing
* File format, particular way that informatio ...
since MS-DOS 1.25
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
and PC DOS 2.0
IBM PC DOS, an acronym for IBM Personal Computer Disk Operating System, is a discontinued disk operating system for IBM PC compatibles. It was manufactured and sold by IBM from the early 1980s into the 2000s. Developed by Microsoft, it was also ...
supported an option /O
(for ''old'') to fill the first byte of all directory entries with instead of utilizing the end marker . Thereby. the volume remained accessible under PC DOS 1.0-1.1 1.1 may refer to:
* 1.1.1.1, a Domain Name System service
* 1.1-inch/75-caliber gun
* Falcon 9 v1.1 orbital launch vehicle
* Trabant 1.1, an automobile
* A one-day Category 1 race in the UCI race classifications system
* A software version number, ...
, while formatting took somewhat longer and newer versions of DOS could not take advantage of the considerable speed-up caused by using the end marker .
References
External links
ECMA-107 Volume and File Structure of Disk Cartridges for Information Interchange
identical to ISO/IEC 9293.
Microsoft Extensible Firmware Initiative FAT32 File System Specification, FAT: General Overview of On-Disk Format
* ttps://web.archive.org/web/20131220004435/http://users.iafrica.com/c/cq/cquirke/fat.htm Understanding FATincluding lots of info about LFNs
Detailed Explanation of FAT Boot Sector
Microsoft Knowledge Base Article 140418
Description of the FAT32 File System
Microsoft Knowledge Base Article 154997
FAT12/FAT16/FAT32 file system implementation for *nix
Includes libfat libraries and fusefat, a FUSE file system driver
MS-DOS: Directory and Subdirectory Limitations
Microsoft Knowledge Base Article 39927
Overview of FAT, HPFS, and NTFS File Systems
Microsoft Knowledge Base Article 100108
''Volume and file size limits of FAT file systems''
Microsoft Technet, copy made b
Internet Archive Wayback Machine
Microsoft TechNet: A Brief and Incomplete History of FAT32
by Raymond Chen
Raymond T. Chen (born 1968) is a United States circuit judge of the United States Court of Appeals for the Federal Circuit.
Biography
He joined the intellectual property law firm of Knobbe, Martens, Olson & Bear in Irvine, California. He prosecu ...
FAT32 Formatter
: allows formatting volumes larger than with FAT32 under Windows 2000
Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It was the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RTM), releas ...
, Windows XP
Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Windows 2000 for high-end and ...
and Windows Vista
Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...
Fdisk does not recognize full size of hard disks larger than
Microsoft Knowledge Base Article 263044, copy made b
Internet Archive Wayback Machine
Explains inability to work with extremely large volumes under Windows 95/98.
Microsoft Windows XP: FAT32 File System
Copy made b
Internet Archive Wayback Machine
of an article with summary of limits in FAT32 which is no longer available on Microsoft website.
Visual Layout of a FAT16 drive
{{ISO standards
1980 software
Computer file systems
Disk file systems
DOS technology
Windows components
Windows disk file systems
Ecma standards
File systems supported by the Linux kernel
fr:File Allocation Table#Aspect technique