File Allocation Table (FAT) is a patented^[5] file system developed by Microsoft for MS-DOS and is the primary file system for consumer versions of Microsoft Windows up to and including Windows Me. A software developer is a programmer who is concerned with one or more facets of the software development process, a somewhat broader scope of computer programming. ... Microsoft Corporation (NASDAQ: MSFT, SEHK: 4338) is an international computer technology corporation with 2005 global annual sales of close to $40 billion USD and about 64,000 employees in 85 countries and regions which develops, manufactures, licenses, and supports a wide range of software products for computing devices. ... Microsoft BASIC is the foundation product of the Microsoft company. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Windows 95 (codename Chicago) is a hybrid 16-bit/32-bit graphical user interface-based operating system released on August 24, 1995 by the Microsoft Corporation. ... In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ... The master boot record (MBR), also the partition sector, in IBM PC architecture, is the 512-byte (1/2 kilobyte) boot sector, i. ... The master boot record (MBR), also the partition sector, in IBM PC architecture, is the 512-byte (1/2 kilobyte) boot sector, i. ... The master boot record (MBR), also the partition sector, in IBM PC architecture, is the 512-byte (1/2 kilobyte) boot sector, i. ... GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical hard disk. ... dyn and The_Decryptors retarded way of saying megabyte. ... A gibibyte is a unit of information or computer storage. ... A gibibyte is a unit of information or computer storage. ... dyn and The_Decryptors retarded way of saying megabyte. ... A gibibyte is a unit of information or computer storage. ... A tebibyte is a unit of information or computer storage, commonly abbreviated TiB. 1 tebibyte = 240 bytes = 1,099,511,627,776 bytes The tebibyte is closely related to the terabyte, which can either be a synonym for tebibyte, or refer to 1012 bytes = 1,000,000,000,000 bytes... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... 1980 (MCMLXXX) was a leap year starting on Tuesday. ... December 31 is the 365th day of the year (366th in leap years) in the Gregorian Calendar. ... (Redirected from 2107) (21st century - 22nd century - 23rd century - other centuries) The twenty-second century comprises the years 2101 to 2200. ... In computing, a fork is additional data associated with a file system object. ... Most modern file systems have methods of administering permissions or access rights to specific users and groups of users. ... Stac Electronics was an engineering company founded in 1984 by four friends at Caltech. ... This article contains information that has not been verified and thus might not be reliable. ... This article contains information that has not been verified and thus might not be reliable. ... DR-DOS is a DOS-family-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildalls Digital Research and derived from CP/M-86. ... A patent is a set of exclusive rights granted by a state to a person for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which is new, inventive, and... In computing, a file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... Microsoft Corporation (NASDAQ: MSFT, SEHK: 4338) is an international computer technology corporation with 2005 global annual sales of close to $40 billion USD and about 64,000 employees in 85 countries and regions which develops, manufactures, licenses, and supports a wide range of software products for computing devices. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Microsoft Windows is a series of popular proprietary operating environments and operating systems created by Microsoft for use on personal computers and servers. ... Windows Millennium Edition (originally codenamed Millennium), also known as Windows Me, is a 16-bit/32-bit graphical operating system released on September 14, 2000 by Microsoft. ...

The FAT file system is considered relatively uncomplicated, and is consequently supported by virtually all existing operating systems for personal computers. This ubiquity makes it an ideal format for floppy disks and solid-state memory cards, and a convenient way of sharing data between disparate operating systems installed on the same computer (a multiboot environment). An operating system is a special computer program that manages the relationship between application software, the wide variety of hardware that makes up a computer system, and the user of the system. ... A floppy disk is a data storage device that is composed of a ring of thin, flexible (i. ... A 32 MB High Speed CompactFlash Type I card A memory card or flash memory card is a solid-state electronic flash memory data storage device used with digital cameras, handheld and laptop computers, telephones, music players, video game consoles, and other electronics. ...

The most common implementations have a serious drawback in that when files are deleted and new files written to the media, their fragments tend to become scattered over the entire media making reading and writing a slow process. De-fragmentation is one solution to this, but is often a lengthy process in itself and has to be repeated regularly to keep the FAT file system clean.

History

The FAT filesystem uses software methods that had been in use years prior to its formalization and was created by Bill Gates and Marc McDonald in 1977 for managing disks in Microsoft Disk BASIC and was incorporated by Tim Paterson in August 1980 to his 86-DOS operating system for the S-100 8086 CPU boards; the filesystem was the main difference between 86-DOS and CP/M, of which 86-DOS was otherwise mostly a clone.^[1] Skeeter samson William Henry Gates III (born October 28, 1955) is the co-founder, chairman, and chief software architect of Microsoft Corporation, the worlds largest software company (as of April 2006). ... Was Microsofts first employee. ... Microsoft BASIC is the foundation product of the Microsoft company. ... Tim Paterson Tim Paterson (born 1956) is an American computer programmer, best known as the original author of the popular MS-DOS operating system. ... QDOS, the Quick and Dirty Operating System, (not to be confused with Sinclairs QDOS for the Sinclair QL computer, which shared the same name) was a simple 16-bit operating system originally written in just four months by Tim Paterson in 1980 for an Intel 8086-based computer kit... The S-100 bus, IEEE696-1983 (withdrawn), was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer. The S-100 bus was the first industry standard bus for the microcomputer industry, and S-100 computers, processor... The 8086 is a 16-bit microprocessor chip designed by Intel in 1978, which gave rise to the x86 architecture. ... CP/M is an operating system originally created for Intel 8080/85 and Zilog Z80 based microcomputers by Gary Kildall of Digital Research, Inc. ...

FAT12

This initial version of FAT is now referred to as FAT12. As a filesystem for floppy disks, it had a number of limitations: no support for hierarchical directories, cluster addresses were "only" 12-bits long (which made the code manipulating the FAT a bit tricky) and the disk size was stored as a 16-bit count of sectors, which limited the size to 32MB. In certain filesystem types like the File Allocation Table (FAT) filesystem of MS-DOS or the NTFS filesystem of Windows NT, a cluster is the unit of disk space allocation for files and directories. ... Cylinder-head-sector, also known as CHS, is a method of addressing data on a hard drive. ...

An entry-level diskette at the time would be 5.25", single-sided, 40 tracks, with 8 sectors per track, resulting in a capacity of slightly less than 160KB. The above limits exceeded this capacity by one or more orders of magnitude and at the same time allowed to fit all the control structures inside the first track, thus avoiding head movement during read and write operations. The limits were successively lifted in the following years. Cylinder-head-sector, also known as CHS, is a method of addressing data on a hard drive. ...

Since the sole root directory had to fit inside the first track as well, the maximum possible number of files was limited to a few dozens.

Directories

In order to properly support the newer IBM PC XT computer, which featured a 10 MB hard disk, MS-DOS 2.0 was released around the same time, at the beginning of 1983, and introduced hierarchical directories. Apart from allowing for better organisation of files, directories allowed it to store many more files on the hard disk, as the maximum number of files was no longer constrained by the (still fixed) root directory size. This number could now be equal to the number of clusters (or even greater, given that zero-sized files do not use any clusters on FAT). The IBM Personal Computer XT (IBM 5160), often shortened to the PC XT or simply XT, was IBMs successor to the original IBM PC. It was released on March 8, 1983, and was one of the first computers to come standard with a hard drive. ...

The format of the FAT itself did not change. The 10 MB hard disk on the PC XT had 4 KB clusters. If a 20 MB hard disk was later installed, and formatted with MS-DOS 2.0, the resultant cluster size would be 8 KB, the boundary at 15.9 MB.

Initial FAT16

In 1984 IBM released the PC AT, which featured a 20 MB hard disk. Microsoft introduced MS-DOS 3.0 in parallel. Cluster addresses were increased to 16-bit, allowing for a greater number of clusters (up to 65,517) and consequently much greater filesystem sizes. However, the maximum possible number of sectors and the maximum (partition, rather than disk) size of 32 MB did not change. Therefore, although technically already "FAT16", this format was not yet what today is commonly understood under this name. A 20 MB hard disk formatted under MS-DOS 3.0, was not accessible by the older MS-DOS 2.0. Of course, MS-DOS 3.0 could still access MS-DOS 2.0 style 8 KB cluster partitions.

MS-DOS 3.0 also introduced support for high-density 1.2 MB 5.25" diskettes, which notably had 15 sectors per track, hence more space for FAT. This probably prompted a dubious optimization of the cluster size, which went down from 2 sectors to just 1. The net effect was that high density diskettes were significantly slower than older double density ones.

Extended partition and logical drives

Apart from improving the structure of the FAT filesystem itself, a parallel development allowing an increase in the maximum possible FAT storage space was the introduction of disk partitions. PC hard disks can only have up to 4 primary partitions, due to the fixed structure of the partition table in the master boot record (MBR). However, by design choice DOS would only use the partition marked as active, which was also the one the MBR would boot. It was not possible to create multiple primary DOS partitions using DOS tools, and third party tools would warn that such a scheme would not be compatible with DOS. In the IBM PC architecture the Master Boot Record (MBR), or partition sector, is the 512-byte boot sector, i. ...

To allow the use of more partitions in a compatible way a new partition type was introduced (in MS-DOS 3.2, January 1986), the extended partition, which was actually just a container for additional partitions called logical drives. Originally only 1 logical drive was possible, allowing the use of hard-disks up to 64 MB. In MS-DOS 3.3 (August 1987) this limit was increased to 24 drives; it probably came from the compulsory letter-based C: - Z: disk naming. The logical drives were described by on-disk structures which closely resemble MBRs, probably to simplify coding, and they were chained/nested in a way analogous to Russian matryoshka dolls. Only one extended partition was allowed. Matryoshka dolls Modern Japanese nested dolls Matryoshka doll disassembled A matryoshka doll A Matryoshka doll (Cyrillic матрёшка or матрешка) is a Russian nesting doll. ...

Prior to the introduction of extended partitions, some hard disk controllers (which at that time were separate option boards, since the IDE standard did not yet exist) could make large hard disks appear as two separate disks. Alternatively, special software drivers, like Ontrack's Disk Manager could be installed for the same purpose ATA cables: 40 wire ribbon cable top, 80 wire ribbon cable bottom Advanced Technology Attachment (ATA) is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. ...

Final FAT16

Finally in November 1987, in Compaq DOS 3.31, came what is today called the FAT16 format, with the expansion of the 16-bit disk sector index to 32 bits. The result was initially called the DOS 3.31 Large File System. Although the on-disk changes were apparently minor, the entire DOS disk code had to be converted to use 32-bit sector numbers, a task complicated by the fact that it was written in 16-bit assembly language. Compaq was a personal computer company founded in 1982 by Rod Canion, Jim Harris and Bill Murto. ...

In 1988 the improvement became more generally available through MS-DOS 4.0. The limit on partition size was now dictated by the 8-bit signed count of sectors-per-cluster, which had a maximum power-of-two value of 64. With the usual hard disk sector size of 512 bytes, this gives 32 KB clusters, hence fixing the "definitive" limit for the FAT16 partition size at 2 gigabytes. On magneto-optical media, which can have 1 or 2 KB sectors, the limit is proportionally greater. A gigabyte (derived from the SI prefix giga-) is a unit of information or computer storage equal to one billion bytes. ... Magneto-optical disc A Magneto-optical disc and the numerous rectangles on its surface A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon magneto-optical discs. ...

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 anyway, generated massive internal fragmentation. Windows 98 also supported reading and writing this variant, but its disk utilities didn't work with it. In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ...

Long File Names (VFAT, LFNs)

One of the "user experience" goals for the designers of Windows 95 was the ability to use long file names (LFNs), in addition to classic 8.3 names. LFNs were implemented using a work-around in the way directory entries are laid out (see below). The version of the file system with this extension is usually known as VFAT after the Windows 95 VxD device driver. 8. ... In Microsoft computing, a VxD is a virtual device driver. ...

Interestingly, the VFAT driver actually appeared before Windows 95, in Windows for Workgroups 3.11, but was only used for implementing 32-bit File Access, a higher performance protected mode file access method, bypassing DOS and directly using either the BIOS, or, better, the Windows-native protected mode disk drivers. It was a backport; Microsoft's ads for WfW 3.11 said 32-bit File Access was based on "the 32-bit file system from our Chicago project". A typical Windows 3. ... 32-bit File Access was a higher performance, protected mode file management introduced in Windows for Workgroups 3. ... Protected mode is an operational mode of x86-compatible CPUs of the 80286 series or later. ... Phoenix AwardBIOS on a standard PC BIOS, santiago in computing, stands for Basic Input/Output System or Basic Integrated Operating System. ... Backporting is the action of taking a certain software modification (patch) and applying it to an older version of the software than it was initially created for. ...

In Windows NT, support for long file names on FAT started from version 3.5.

FAT32

In order to overcome the volume size limit of FAT16, while still allowing DOS real-mode code to handle the format without unnecessarily reducing the available conventional memory, Microsoft decided to implement a newer generation of FAT, known as FAT32, with cluster counts held in a 32-bit field, of which 28 bits are currently used. Conventional Memory is the first 640 kilobytes of an IBM PCs memory. ...

In theory, this should support a total of approximately 268,435,438 (< 2²⁸) clusters, allowing for drive sizes in the range of 2 terabytes. However, due to limitations in Microsoft's scandisk utility, the FAT is not allowed to grow beyond 4,177,920 (< 2²²) clusters, placing the volume limit at 124.55 gigabytes, unless "scandisk" is not needed ^[2]. A terabyte (derived from the SI prefix tera-) is a measurement term for data storage capacity equal to approximately 1000 Gigabytes. ... SCANDISK or Scandisk is a command in MS-DOS and Microsoft Windows systems which verifies hard disk or floppy disk for file system integrity. ... A gigabyte (derived from the SI prefix giga-) is a unit of information or computer storage equal to one billion bytes. ...

FAT32 was introduced with Windows 95 OSR2, although reformatting was needed to use it, and DriveSpace 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 NT line, support for FAT32 arrived in Windows 2000. This article contains information that has not been verified and thus might not be reliable. ...

Windows 2000 and Windows XP can read and write to FAT32 filesystems of any size, but the format program on these platforms can only create FAT32 filesystems up to 32GB. Thompson and Thompson (2003) write^[3] that "Bizarrely, Microsoft states that this behavior is by design." Microsoft's knowledge base article 184006^[2] indeed confirms the limitation, but gives no rationale or explanation. Peter Norton's opinion^[4] is that "Microsoft has intentionally crippled the FAT32 file system." Peter Norton Peter Norton (born November 14, 1943) is an American software publisher and philanthropist. ...

The maximum possible size for a file on a FAT32 volume is 4GiB minus 1B (2³²-1 bytes). For most users, this has become the most nagging limit of FAT32 as of 2005, since video capture and editing applications can easily exceed this limit, as can the system swap file. 2005 is a common year starting on Saturday of the Gregorian calendar. ... Virtual memory is intended to help the programmer by taking care of some memory housekeeping duties. ...

Third party support

The alternative IBM PC operating systems — such as Linux, FreeBSD, and BeOS — have all supported FAT, and most added support for VFAT and FAT32 shortly after the corresponding Windows versions were released. Early Linux distributions also supported a format known as UMSDOS, which was FAT with Unix file attributes (such as long file name and access permissions) stored in a separate file called --linux-.---. UMSDOS fell into disuse after VFAT was released and is not enabled by default in Linux kernels from version 2.5.7 onwards [6]. The Mac OS X operating system also supports the FAT filesystems on volumes other than the boot disk. Unix systems filiation. ... FreeBSD is a Unix-like free software operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD) branch through 386BSD and 4. ... BeOS is an operating system for personal computers which began development by Be Incorporated in 1991. ... UMSDOS is a filesystem driver for Linux that simulates the more advanced features of a UNIX filesystem while using an MS-DOS style FAT partition. ... The Linux kernel is a free software Unix-like operating system kernel that was begun by Linus Torvalds in 1991 and subsequently improved with the assistance of developers around the world. ... This article or section does not cite its references or sources. ... A boot disk is a removable media, normally read-only, that can boot an operating system or utility. ...

FAT and Alternate Data Streams

The FAT filesystem itself is not designed for supporting ADS, but some operating systems that heavily depend on them have devised various methods for handling them in FAT drives. Such methods either store the additional information in extra files and directories (Mac OS), or give new semantics to previously unused fields of the FAT on-disk data structures (OS/2 and Windows NT). The second design, while presumably more efficient, prevents any copying or backing-up of those volumes using non-aware tools; manipulating such volumes using non-aware disk utilities (e.g. defragmenters or CHKDSK) will probably lose the information. In computing, a fork is additional data associated with a file system object. ... CHKDSK (command shortening of Checkdisk) is a command in DOS and Microsoft Windows systems which verifies a hard disk or a floppy disk for file system integrity. ...

Mac OS using PC Exchange stores its various dates, file attributes and long filenames in a hidden file called FINDER.DAT, and Resource 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. Mac OS, which stands for Macintosh Operating System, is a series of graphical user interface-based operating systems developed by Apple Computer for their Macintosh line of computer systems. ... PC Exchange was a Macintosh capatibilty utility, that let you use MS-DOS-format disks on a Macintosh. ...

Mac OS X stores metadata (Resource Forks, file attributes, other ADS) in a hidden file with a name constructed from the owner filename prefixed with "._", and Finder stores some folder and file metadata in a hidden file called ".DS_Store". This article or section does not cite its references or sources. ...

OS/2 heavily depends on extended attributes (EAs) and stores them in a hidden file called "EA DATA. SF" in the root directory of the FAT12 or FAT16 volume. This file is indexed by 2 previously reserved bytes in the file's (or directory's) directory entry. In the FAT32 format, these bytes hold the upper 16 bits of the starting cluster number of the file or directory, hence making it difficult to store EAs on FAT32. Extended attributes are accessible via the Workplace Shell desktop, through REXX scripts, and many system GUI and command-line utilities (such as 4OS2). OS/2 was an operating system created by Microsoft and IBM and later developed by IBM exclusively. ... The OS/2 Warp 4 desktop (with some third-party enhancements installed as SOM classes) The Workplace Shell (WPS) is an award-winning object-oriented desktop shell produced by IBMs Boca Raton development lab for OS/2 2. ... REXX (REstructured eXtended eXecutor) is an interpreted programming language which was developed at IBM. It is a structured high-level programming language which was designed to be both easy to learn and easy to read. ... A graphical user interface (or GUI, sometimes pronounced gooey) is a method of interacting with a computer through a metaphor of direct manipulation of graphical images and widgets in addition to text. ... CLI is an acronym (or, strictly speaking, an initialism) for Command line interface Call Level Interface Common language interface (Commonly believed, but not official for Common Language Infrastructure) Common Language Infrastructure CLear Interrupts Composite Leading Indicator Caller Line Identification (telephony) Celebrity Love Island Critical Language Institute This page concerning a... 4DOS is a command line interpreter by JP Software originally designed to replace the DOS default command. ...

Windows NT supports the handling of extended attributes in HPFS, NTFS, and FAT. It stores EAs on FAT using exactly the same scheme as OS/2, but does not support an other kind of ADS as held on NTFS volumes. Trying to copy a file with any ADS other than EAs from an NTFS volume to a FAT volume gives a warning message with the names of the ADSs that will be lost. Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. ... HPFS or High Performance File System, is a file system created specifically for the OS/2 operating system to improve upon the limitations of the FAT file system. ... NTFS or New Technology File System is the standard file system of Windows NT and its descendants Windows 2000, Windows XP and Windows Server 2003. ...

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"). Windows 2000 (also referred to as Win2K, W2K or Windows NT 5. ...

Future

Microsoft has recently secured patents for VFAT and FAT32 (but not the original FAT), which is causing concern that they might later seek royalties from Linux distros and from media vendors that pre-format their products (see FAT Licensing below). Despite two earlier rulings against them, Microsoft prevailed and were awarded the patents.

Since Microsoft has announced the discontinuation of its MS-DOS-based consumer operating systems with Windows Me, it remains unlikely that any new versions of FAT will appear. For most purposes, the NTFS file system that was developed for the Windows NT line is superior to FAT from the points of view of efficiency, performance and reliability; its main drawbacks are the size overhead for small volumes and the very limited support by anything other than the NT-based versions of Windows, since the exact specification is a trade secret of Microsoft, which in turn makes it difficult to use a DOS floppy for recovery purposes. Microsoft provided a recovery console to work around this issue, but they severely limited what could be done through it by default for security reasons. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... NTFS or New Technology File System is the standard file system of Windows NT and its descendants Windows 2000, Windows XP and Windows Server 2003. ... A trade secret is a formula, practice, process, design, instrument, pattern, or compilation of information used by a business to obtain an advantage over competitors within the same industry or profession. ...

FAT is still the normal filesystem for removable media (with the exception of CDs and DVDs), with FAT12 used on floppies, and FAT16 on most other removable media (such as flash memory cards for digital cameras and USB flash drives). Most removable media is not yet large enough to benefit from FAT32, although some larger flash drives do make use of it. FAT is used on these drives for reasons of compatibility and size overhead, as well as the fact that file permissions on removable media are likely to be more trouble than they are worth. A USB Flash Memory Device Flash memory is a form of EEPROM (Electrically Erasable Programmable Read-Only Memory) that allows multiple memory locations to be erased or written in one programming operation. ... A SiPix digital camera next to a matchbox to show scale. ... Note: USB may also mean upper sideband in radio. ...

The FAT32 formatting support in Windows 2000 and XP is limited to drives of 32 gigabytes, which effectively forces users of modern hard drives either to use NTFS or to format the drive using other tools outside Windows. A workaround to this involves using a version of mkdosfs that has been ported from Linux to Windows.

There is also a free and open source utility available here.

Design

Main disk structures

A FAT file system is composed of four different sections.

1. The Reserved sectors, located at the very beginning. The first reserved sector is the Boot Sector (aka Partition Boot Record). It includes an area called the BIOS Parameter Block (with 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 code. The total count of reserved sectors is indicated by a field inside the Boot Sector. Important information from the Boot Sector is accessible thru an operating system structure called the Drive Parameter Block in DOS and OS/2.
2. The FAT Region. This contains two copies of the File Allocation Table for the sake of redundancy, although the extra copy is rarely used, even by disk repair utilities. These are maps of the partition, indicating how the clusters are allocated.
3. The Root Directory Region. This is a Directory Table that stores information about the files and directories in the root directory. With FAT32 it can be stored anywhere in the partition, however with earlier versions it is always located immediately after the FAT Region.
4. The Data Region. This is where the actual file and directory data is stored and takes up most of the partition. 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. Note however, that each cluster can be taken only by one file, and so if a 1 KB file resides in a 32 KB cluster, 31 KB are wasted.

The boot sector is a region (typically the first 512 bytes) of a hard disk, floppy disk, or similar data storage device, or a partition thereof. ...

Boot Sector

The Boot Sector is of the following format: The boot sector is a region (typically the first 512 bytes) of a hard disk, floppy disk, or similar data storage device, or a partition thereof. ...

The boot sector is portrayed here as found on e.g. an OS/2 1.3 boot diskette. Earlier versions used a shorter BIOS Parameter Block and their boot code would start earlier (for example at offset 0x2b in OS/2 1.1).

Exceptions

The implementation of FAT used in MS-DOS for the Apricot PC 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 filesystem parameters (offsets 0x0B - 0x17 in the standard sector) were located at offset 0x50. 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. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... The Apricot PC was Apricot Computers first personal computer made for business use. ... Phoenix AwardBIOS on a standard PC BIOS, santiago in computing, stands for Basic Input/Output System or Basic Integrated Operating System. ...

DOS Plus on the BBC Master 512 did not use conventional boot sectors at all. Data disks omitted the boot sector and began with a single copy of the FAT (the first byte of the FAT was used to determine disk capacity) while boot disks began with a miniature ADFS filesystem containing the boot loader, followed by a single FAT. It could also access standard PC disks formatted to 180 KB or 360 KB, again using the first byte of the FAT to determine capacity. DOS Plus (also known as DOS+) is an operating system written by Digital Research, first released in 1985. ... A BBC Master 128 with monitor and disk drives. ... In computing, ADFS stands for the Advanced Disc Filing System. ...

File Allocation Table

A partition is divided up 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 partition, typically cluster sizes lie somewhere between 2 KB and 32 KB. Each file may occupy one or more of these clusters depending on its size; thus, a file is represented by a chain of these clusters (referred to as a singly linked list). However these chains are not necessarily stored adjacent to one another on the disk's surface but are often instead fragmented throughout the Data Region. In computer science, a linked list is one of the fundamental data structures used in computer programming. ...

The File Allocation Table (FAT) is a list of entries that map to each cluster on the partition. Each entry records one of five things:

• the address of the next cluster in a chain
• a special end of file (EOF) character that indicates the end of a chain
• a special character to mark a bad cluster
• a special character to mark a reserved cluster
• a zero to note that that cluster is unused

Each version of the FAT file system uses a different size for FAT entries. The size is indicated by the name, for example the FAT16 file system uses 16 bits for each entry while the FAT32 file system uses 32 bits. This difference means that the File Allocation Table of a FAT32 system can map a greater number of clusters than FAT16, allowing for larger partition sizes with FAT32. This also allows for more efficient use of space than FAT16, because on the same hard drive a FAT32 table can address smaller clusters which means less wasted space.

FAT entry values:

Note that FAT32 uses only 28 bits of the 32 possible bits. The upper 4 bits are usually zero but are reserved and should be left untouched. In the table above these are denoted by a question mark.

The first cluster of the data area is cluster #2. That leaves the first two entries of the FAT unused. In the first byte of the first entry a copy of the media descriptor is stored. The remaining bits of this entry are 1. In the second entry the end-of-file marker is stored. The high order two bits of the second entry are sometimes, in the case of FAT16 and FAT32, used for dirty volume management: high order bit 1: last shutdown was clean; next highest bit 1: during the previous mount no disk I/O errors were detected.^[5]

Directory table

A directory table is a special type of file that represents a directory (nowadays commonly known as a folder). Each file or directory stored within it is represented by a 32 byte entry in the table. Each entry records the name, extension, attributes (archive, directory, hidden, read-only, system and volume), the date and time of creation, the address of the first cluster of the file/directory's data and finally the size of the file/directory.

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.

Legal characters for DOS file names include the following:

• Upper case letters A-Z
• Numbers 0-9
• Space (though trailing spaces are considered to be padding and not a part of the file name)
•  ! # $ % & ( ) - @ ^ _ ` { } ~ '
• Values 128-255

The DOS file names are in the OEM character set. Code page is the traditional IBM term used for a specific character encoding table: a mapping in which a sequence of bits, usually a single octet representing integer values 0 through 255, is associated with a specific character. ...

Directory entries, both in the Root Directory Region and in subdirectories, are of the following format:

Long File Names (LFN) are stored on a FAT file system using a trick - adding phoney entries into the Directory Tables. The entries are marked with a Volume Label attribute which is impossible for a regular file and because of that they are ignored by most old MS-DOS programs. 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. OS/2 was an operating system created by Microsoft and IBM and later developed by IBM exclusively. ...

A checksum 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. (Note that 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 a space (ASCII 0x20) char. For example, "Readme.txt" would be "README  TXT".) A checksum is a form of redundancy check, a very simple measure for protecting the integrity of data by detecting errors in data that is sent through space (telecommunications) or time (storage). ...

 unsigned char lfn_checksum(const unsigned char *pFcbName) { int i; unsigned char sum=0; for (i=11; i; i--) sum = ((sum & 1) ? 0x80 : 0) + (sum >> 1) + *pFcbName++; return sum; } 

Older versions of PC-DOS mistake LFN names in the root directory for the volume label, and are likely to display an incorrect label.

Each phoney entry can contain up to 13 UTF-16 characters (26 bytes), gaining about 15 bytes in addition to the old 8 + 3 by using fields in the record which contained file size or time stamps (but for security versus disk checking tools the starting cluster field is left unused with a 0 value). See 8.3 for additional explanations. In computing, UTF-16 is a 16-bit Unicode Transformation Format, a character encoding form that provides a way to represent a series of abstract characters from Unicode and ISO/IEC 10646 as a series of 16-bit words suitable for storage or transmission via data networks. ... 8. ...

LFN entries use the following format:

If a filename contains only lowercase letters, or is a combination of a lowercase basename with an uppercase extension, or vice-versa, has no special characters, and fits within the 8.3 limits, a VFAT entry is not created on Windows NT. Instead, undocumented bits in byte 0x0c 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 this. Non-NT Windows versions see all-uppercase filenames if this extension has been used. By default, recent versions of Linux will recognize this extension but won't use it when writing. In computing, UTF-16 is a 16-bit Unicode Transformation Format, a character encoding form that provides a way to represent a series of abstract characters from Unicode and ISO/IEC 10646 as a series of 16-bit words suitable for storage or transmission via data networks. ... In computing, UTF-16 is a 16-bit Unicode Transformation Format, a character encoding form that provides a way to represent a series of abstract characters from Unicode and ISO/IEC 10646 as a series of 16-bit words suitable for storage or transmission via data networks. ... In computing, UTF-16 is a 16-bit Unicode Transformation Format, a character encoding form that provides a way to represent a series of abstract characters from Unicode and ISO/IEC 10646 as a series of 16-bit words suitable for storage or transmission via data networks. ...

Third-party extensions

Before Microsoft added support for long filenames and creation/access time stamps, bytes 0x0C-0x15 of the directory entry were used by alternative operating systems to store additional metadata. These included:

RISC OS, which stands for Reduced Instruction Set Computing Operating System is a British Graphical user interface-based operating system for ARM-processor based computers or similar devices. ... DOS Plus (also known as DOS+) is an operating system written by Digital Research, first released in 1985. ... DR-DOS is a DOS-family-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildalls Digital Research and derived from CP/M-86. ...

FAT licensing

Microsoft applied for, and was granted, a series of patents for key parts of the FAT file system in the mid-1990s. Being almost universally compatible and well-understood, FAT is frequently chosen as an interchange format for flash media used in digital cameras and PDAs. Flash memory is a form of EEPROM that allows multiple memory locations to be erased or written in one programming operation. ... A SiPix digital camera next to a matchbox to show scale. ... palmOne Tungsten T5 Personal digital assistants (also called PDAs) are handheld devices that were originally designed as personal organizers, but became much more versatile over the years. ...

On 2003-12-03 Microsoft announced it would be offering licenses for use of its FAT specification and "associated intellectual property", at the cost of a US $0.25 royalty per unit sold, with a $250,000 maximum royalty per license agreement. 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... December 3 is the 337th (in leap years the 338th) day of the year in the Gregorian calendar. ...

To this end, Microsoft cited four patents on the FAT filesystem as the basis of its intellectual property claims. All four pertain to long-filename extensions to FAT first seen in Windows 95: Windows 95 (codename Chicago) is a hybrid 16-bit/32-bit graphical user interface-based operating system released on August 24, 1995 by the Microsoft Corporation. ...

• U.S. Patent 5,745,902 - Method and system for accessing a file using file names having different file name formats. Filed July 6, 1992. This covered a means of generating and associating a short, 8.3-compatible filename with long one (for example, "Microsoft.txt" with "MICROS~1.TXT") and a means of enumerating conflicting short filenames (for example, "MICROS~2.TXT" and "MICROS~3.TXT"). It is unclear whether this patent would cover an implementation of FAT without explicit long filename capabilities. Hard links in Unix file systems do not appear to be prior art: deleting a FAT file via its long name will also remove its short name. Renaming a file to a "short" name also updates the long file name for coherency; similarly, renaming a file to a "long" name will allocate a new "short" name. In NTFS, hard links and dual names are separate concepts and each hard link has two names. Finally, at the API level, both names are always provided together when a directory lookup is requested from the system; they do not appear as two separate files and do not have to be "matched" to determine unique files.
• U.S. Patent 5,579,517 - Common name space for long and short filenames. Filed for on 1995-04-24. This covers the method of chaining together multiple consecutive 8.3 directory entries to hold long filenames, with some of the entries specially marked to prevent their confusing older, long filename-unaware FAT implementations.
  • The Public Patent Foundation successfully challenged this patent; the claims were rejected^[6] on 2004-09-14, due to prior disclosure^[7] of the claimed techniques in patents U.S. Patent 5,307,494 and U.S. Patent 5,367,671. This decision was later overturned by the Patent Office on 2006-01-10.
• U.S. Patent 5,758,352 - Common name space for long and short filenames. Filed on 1996-09-05. This is very similar to 5,579,517.
  • The Public Patent Foundation successfully challenged this patent; The USPTO rejected this patent on 2005-10-05, on the grounds that "the six assignees names were incorrect"^[8][9]. This decision was also later overturned by the Patent Office on 2006-01-10.
• U.S. Patent 6,286,013 - Method and system for providing a common name space for long and short file names in an operating system. Filed on 1997-01-28. This makes claims on the methods used when Windows 95, Windows 98 and Windows Me expose long filenames to their MS-DOS compatibility layer. It does not appear to affect any non-Microsoft FAT implementations.

Many technical commentators have concluded that these patents only cover FAT implementations that include support for long filenames, and that removable solid state media and consumer devices only using short names would be unaffected. July 6 is the 187th day of the year (188th in leap years) in the Gregorian Calendar, with 178 days remaining. ... 1992 (MCMXCII) was a leap year starting on Wednesday. ... 8. ... In computing, a hard link is a reference, or pointer, to the physical data on a volume. ... Wikibooks has more about this subject: Guide to Unix Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... In most patent laws, prior art or state of the art is all information that has been disclosed to the public in any form before a given date. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... April 24 is the 114th day of the year in the Gregorian Calendar (115th in leap years). ... 8. ... Public Patent Foundation, or PUBPAT, is a nonprofit organization that seeks to limit perceived abuse of the U.S. Patent system. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... September 14 is the 257th day of the year in the Gregorian calendar (258th in leap years). ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... January 10 is the 10th day of the year in the Gregorian calendar. ... 1996 (MCMXCVI) was a leap year starting on Monday of the Gregorian calendar, and was designated the International Year for the Eradication of Poverty. ... September 5 is the 248th day of the year (249th in leap years). ... Public Patent Foundation, or PUBPAT, is a nonprofit organization that seeks to limit perceived abuse of the U.S. Patent system. ... The United States Patent and Trademark Office (PTO or USPTO) is an agency in the United States Department of Commerce that provides patent and trademark protection to inventors and businesses for their inventions and corporate and product identification. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... October 5 is the 278th day of the year (279th in Leap years). ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... January 10 is the 10th day of the year in the Gregorian calendar. ... 1997 (MCMXCVII in Roman) is a common year starting on Wednesday of the Gregorian calendar. ... January 28 is the 28th day of the year in the Gregorian calendar. ... Windows 95 (codename Chicago) is a hybrid 16-bit/32-bit graphical user interface-based operating system released on August 24, 1995 by the Microsoft Corporation. ... Windows 98 (codename Memphis) is a graphical operating system released on June 25, 1998 by Microsoft. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ...

Additionally, in the document "Microsoft Extensible Firmware Initiative FAT 32 File System Specification, FAT: General Overview of On-Disk Format" published by Microsoft (version 1.03, 2000-12-06), Microsoft specifically grants a number of rights, which many readers have interpreted as permitting operating system vendors to implement FAT. This article is about the year 2000. ... December 6 is the 340th day (341st on leap years) of the year in the Gregorian calendar. ...

Microsoft is not the only company to have applied for patents for parts of the FAT file system. Other patents affecting FAT include:

• U.S. Patent 5,367,671 - System for accessing extended object attribute (EA) data through file name or EA handle linkages in path tables. Filed on 1990-09-25 by Barry A. Feigenbaum and Felix Miro of IBM, this makes claims on the methods used by OS/2, Windows NT, and Linux for storing extended attribute data in the "EA DATA. SF" file.

This article is about the year. ... September 25 is the 268th day of the year (269th in leap years). ... OS/2 was an operating system created by Microsoft and IBM and later developed by IBM exclusively. ... Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. ... Unix systems filiation. ...

Appeal

As there was widespread call for these patents to be re-examined, the Public Patent Foundation submitted evidence to the US Patent and Trade Office (USPTO) disputing the validity of these patents, including prior art references from Xerox and IBM. The USPTO acknowledged that the evidence raised "substantial new question[s] of patentability," and opened an investigation into the validity of Microsoft's FAT patents. Public Patent Foundation, or PUBPAT, is a nonprofit organization that seeks to limit perceived abuse of the U.S. Patent system. ... The United States Patent and Trademark Office (PTO or USPTO) is an agency in the United States Department of Commerce that provides patent and trademark protection to inventors and businesses for their inventions and corporate and product identification. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... International Business Machines Corporation (IBM, or colloquially, Big Blue; NYSE: IBM) is a computer technology firm headquartered in Armonk, NY, USA. The company, which was founded in 1888 and incorporated June 15, 1911, manufactures and sells computer hardware, software, infrastructure services, hosting services, and consulting services. ...

On 2004-09-30 the USPTO rejected all claims of U.S. Patent 5,579,517, based primarily on evidence provided by the Public Patent Foundation. Dan Ravicher, the foundation's executive director, said "The Patent Office has simply confirmed what we already knew for some time now, Microsoft's FAT patent is bogus." 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... September 30 is the 273rd day of the year (274th in leap years) in the Gregorian calendar, with 92 days remaining. ... Public Patent Foundation, or PUBPAT, is a nonprofit organization that seeks to limit perceived abuse of the U.S. Patent system. ...

According to the PUBPAT press release, "Microsoft still has the opportunity to respond to the Patent Office's rejection. Typically, third party requests for reexamination, like the one filed by PUBPAT, are successful in having the subject patent either narrowed or completely revoked roughly 70% of the time." Categories: Stub | Consumer organizations ...

On 2005-10-05 the Patent Office announced that, following the re-examination process, it had again rejected all claims of patent 5.579,517, and it additionally found U.S. Patent 5,758,352 invalid on the grounds that the patent had incorrect assignees. 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... October 5 is the 278th day of the year (279th in Leap years). ...

Finally, on 2006-01-10 the Patent Office ruled that features of Microsoft's implementation of the FAT system were "novel and non-obvious" reversing both earlier non-final decisions. 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... January 10 is the 10th day of the year in the Gregorian calendar. ...

Footnotes

• ↑ Patents apply to technology supporting Long File Names (Microsoft) and extended attributes (IBM) within the file system, but not the core file system itself.

References

1. ↑ Duncan, Ray (1989). Design goals and implementation of the new High Performance File System. Microsoft Systems Journal 4 (5).
2. ↑ ^{a b} Limitations of FAT32 File System, Microsoft knowledge base article 184006
3. ↑ Thompson, Robert Bruce and Thompson, Barbara Fritchman; PC Hardware in a Nutshell, 3rd Edition,, O'Reilly, ISBN 059600513X (p. 506: Microsoft "bizarrely" saying the 32GB limitation is by design)
4. ↑ Norton, Peter (2002); Peter Norton's New Inside the PC, Sams Publishing, ISBN 0672322897 (p. 428: "Microsoft has intentionally crippled the FAT32 file system")
5. ↑ "The FAT filesystem: FAT"
6. ↑ [1]
7. ↑ [2]
8. ↑ [3]
9. ↑ [4]

See also

• Comparison of file systems
• Drive letter assignment
• Software patent
• List of file systems
• Rock Ridge and Joliet — systems for CDs that add long file names similar to what vfat did for fat.

This article is in need of attention from an expert on the subject. ... Drive letter assignment is the process of matching volumes (active primary partitions and logical partitions) to letters in the root namespace of a file system as seen by a Microsoft operating system. ... Software patents and patents on computer-implemented inventions (CII) are a class of patents and one of many legal aspects of computing. ... The following lists identify, characterise and link to fuller information on computer file systems. ... The Rock Ridge Interchange Protocol (RRIP, IEEE P1282) is an extension to the ISO 9660 volume format which adds POSIX file system semantics. ... Joliet is the name of an extension to the ISO 9660 file system. ...

External links

• News article about final patent ruling
• Microsoft's statement on "FAT File System Technology and Patent License"
• Slashdot discussion on Microsoft's claims of FAT-related patents
• Microsoft Extensible Firmware Initiative FAT 32 File System Specification, FAT: General Overview of On-Disk Format
• Understanding FAT32 Filesystems (explained for embedded firmware developers)
• Microsoft's war on GPL dealt patent setback
• A Short History of MS-DOS, by Tim Paterson
• Detailed Explanation of FAT Boot Sector - Microsoft Knowledge Base Article 140418
• At PUBPAT's Request, Patent Office Rejects Microsoft's FAT Patent: All Claims of Reynolds '517 Patent Ruled Invalid
• Volume and file size limits of FAT filesystems
• Overcoming FAT 32 Limitations
• Implementation of OS/2 extended attributes on the FAT file system.