File Allocation Table

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FAT
Developer Microsoft, NCR, SCP, IBM, Compaq, Digital Research, Novell, Caldera
Full name File Allocation Table:
FAT12 (12-bit version),
FAT16/FAT16B/FAT16X (16-bit versions),
FAT32/FAT32X (32-bit version with 28 bits used)
Introduced 1977 (Standalone Disk BASIC-80)
FAT12: August 1980 (SCP QDOS)
FAT16: August 1984 (IBM PC DOS 3.0)
FAT16B: November 1987 (Compaq MS-DOS 3.31)
FAT16X: August 1995 (Windows 95)
FAT32/FAT32X: August 1996 (Windows 95 OSR2)
Partition identifier MBR/EBR:
FAT120x01 H:0x11/0x8D S:0xC1/0xD1
FAT160x04 H:0x14/0x90 S:0xC4/0xD4
FAT16B0x06 H:0x16/0x92 S:0xC6/0xD6
FAT16X: 0x0E H:0x1E/0x9A S:0xCE
FAT32: 0x0B H:0x1B/0x97 S:0xCB
FAT32X: 0x0C H:0x1C/0x98 S:0xCC
Logical sectored FAT12/FAT16: 0x08 0x11 0x14 0x24 0x56 0xE5 0xF2
BDP: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Structures
Directory contents Table
File allocation Linked list
Bad blocks Cluster tagging
Limits
Max. volume size FAT12: 32 MiB (256 MiB for 64 KiB clusters)
FAT16: 2 GiB (4 GiB for 64 KiB clusters)
FAT32: 2 TiB (16 TiB for KiB sectors)
Max. file size

4,294,967,295 bytes (4 GiB - 1) with FAT16B and FAT32[1]

274,877,906,943 bytes (256 GiB - 1) only with FAT32+[2]
Max. number of files FAT12: 4,068 for 8 KiB clusters
FAT16: 65,460 for 32 KiB clusters
FAT32: 268,173,300 for 32 KiB clusters
Max. filename length 8.3 filename, or 255 UCS-2 characters when using LFN
Features
Dates recorded Modified date/time, creation date/time (DOS 7.0 and higher only), access date (only available with ACCDATE enabled),[3] deletion date/time (only with DELWATCH 2)
Date range 1980-01-01 to 2099-12-31 (2107-12-31)
Date resolution 2 seconds for last modified time,
10 ms for creation time,
1 day for access date,
2 seconds for deletion time
Forks Not natively
Attributes Read-only, Hidden, System, Volume, Directory, Archive
File system permissions FAT12/FAT16: File, directory and volume access rights for Read, Write, Execute, Delete only with DR-DOS, PalmDOS, Novell DOS, OpenDOS, FlexOS, 4680 OS, 4690 OS, Concurrent DOS, Multiuser DOS, System Manager, REAL/32 (Execute right only with FlexOS, 4680 OS, 4690 OS; individual file / directory passwords not with FlexOS, 4680 OS, 4690 OS; World/Group/Owner permission classes only with multiuser security loaded)
FAT32: Partial, only with DR-DOS, REAL/32 and 4690 OS
Transparent compression FAT12/FAT16: Per-volume, SuperStor, Stacker, DoubleSpace, DriveSpace
FAT32: No
Transparent encryption FAT12/FAT16: Per-volume only with DR-DOS
FAT32: No

File Allocation Table (FAT) is the name of a 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.[4] It offers good performance even in 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 systems for personal computers and many mobile devices and embedded systems, and thus is a well-suited format for data exchange between computers and devices of almost any type and age from 1981 up to the present.

Originally designed in 1977 for use on floppy disks, FAT was soon adapted and used almost universally on hard disks throughout the DOS and Windows 9x eras for two decades. As disk drives evolved, the capabilities of the file system have been extended accordingly resulting in three major file system variants: FAT12, FAT16 and FAT32. The FAT standard has also been expanded in other ways while generally preserving backward compatibility with existing software.

With the introduction of more powerful computers and operating systems, as well as the development of more complex file systems for them, FAT is no longer the default file system for usage on Microsoft Windows computers.[5]

Today, FAT file systems are still commonly found on floppy disks, USB sticks, flash and other solid-state memory cards and modules, and many portable and embedded devices. DCF implements FAT as the standard file system for digital cameras. FAT is also utilized in the boot stage of EFI-compliant computers.

Overview[edit]

Concepts[edit]

The name of the file system originates from the file system's prominent usage of an index table, the File Allocation Table (FAT), statically allocated at the time of formatting. The table contains entries for each cluster, 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 variants of the FAT format are named after the number of table element bits: 12 (FAT12), 16 (FAT16), and 32 (FAT32). Except for the original 8-bit FAT 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.

Uses[edit]

The FAT file system has a long history (over three decades) of usage on desktops and portable computers, and it is frequently used in embedded solutions.

FAT offers reasonably good performance and robustness, even in very light-weight implementations.[4] It is therefore widely adopted and supported by virtually all existing operating systems for personal computers as well as some home computers and a multitude of embedded systems. As such, it continues to be the most widespread file system worldwide. This also makes it a useful format for solid-state memory cards and a convenient way to share data between operating systems.

FAT file systems are the default file system for removable media (with the exception of CDs and DVDs) and as such are commonly found on floppy disks, super-floppies, memory and flash memory cards or USB flash drives and are supported by most portable devices such as PDAs, digital cameras, camcorders, media players, or mobile phones. While FAT12 is omnipresent on floppy disks, FAT16 and FAT32 are typically found on the larger media.

FAT was also commonly used on hard disks throughout the DOS and Windows 9x eras, but its use on hard drives has declined since the introduction of Windows XP, which primarily uses the newer NTFS. FAT is still used in hard drives expected to be used by multiple operating systems, such as in shared Windows, Linux and DOS environments.

Due to the widespread use of FAT-formatted media, many operating systems provide support for FAT through official or third-party file system handlers. For example, OS/2, Linux, FreeBSD and BeOS provide inbuilt support for FAT, even though they also support more sophisticated file systems such as ext4 or btrfs. Mac OS 9 and Mac OS X support FAT file systems on volumes other than the boot disk. AmigaOS supports FAT through the CrossDOS package.

For many purposes, the NTFS file system is superior to FAT in terms of features and reliability; its main drawbacks are its complexity and the size overhead for small volumes as well as the very limited support by anything other than the NT-based versions of Windows, since the exact specification is a trade secret of Microsoft. The availability of NTFS-3G since mid-2006 has led to much improved NTFS support in Unix-like operating systems, considerably alleviating this concern. It is still not possible to use NTFS in DOS-like operating systems without third-party drivers, 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 for security reasons it severely limited what could be done through the Recovery Console by default. The movement of recovery utilities to boot CDs based on BartPE, Linux (with NTFS-3G), or WinPE is eroding this drawback, but the NTFS's complexity forbids its implementation in light-weight operating systems and embedded systems.

The DCF file system adopted by almost all digital cameras since 1998 defines a logical file system with 8.3 filenames and makes the usage of either FAT12, FAT16, FAT32 or exFAT mandantory for its physical layer in order to maximize platform interoperability.[6]

FAT is also utilized internally for the EFI system partition (partition type 0xEF) in the boot stage of EFI-compliant computers.[7]

For floppy disks, FAT has been standardized as ECMA-107[8] and ISO/IEC 9293:1994[9] (superseding ISO 9293:1987[10]). These standards cover FAT12 and FAT16 with only short 8.3 filename support; long filenames with VFAT are partially patented.[11]

Nomenclature[edit]

Technically, the term "FAT file system" refers to all three major variants of the file system, FAT12, FAT16 and FAT32, and most parties clearly distinguish between them where necessary. In contrast to this, Microsoft typically no longer distinguishes between all three of them since the introduction of FAT32, and refers to both FAT12 and FAT16 as "FAT", whereas "FAT32" gets treated specially in dialog boxes and documentation. This can sometimes lead to confusion if the actual type of the file system used is not mentioned or cannot be explicitly specified (e.g., "Do you want to format as FAT or FAT32?" instead of "Do you want to format as FAT12, FAT16 or FAT32?").

Another common cause of confusion exists within the group of FAT16 file systems, since the term "FAT16" refers to both, either the whole group of FAT file systems with 16-bit wide cluster entries, or specifically only the original implementation of it with 16-bit sector entries, when it becomes necessary to differentiate between the original and the later implementation. While technically the newer variant with 32-bit sector entries is called "FAT16B", it is commonly referred to under the name "FAT16" as well, in particular since the original variant is rarely seen today and typically only used on small media when backward compatibility with DOS before 3.31 is required.

Further, the term "VFAT" has led to various misconceptions as well,[nb 1] as it is sometimes erroneously used as if it would describe another variant of FAT file system to be distinguished from the FAT12, FAT16 and FAT32 file systems, while in reality it does not specify another file system, but an optional extension, which can work on top of any FAT file system, FAT12, FAT16 or FAT32. Volumes utilizing VFAT long-filenames can be read also by operating systems not supporting the VFAT extension, for as long as they support the underlying file system.

Yet another cause for misconceptions stems from some apparent redundancy and possible ambiguity in the definition of FAT volumes. The general type of file system (FAT12, FAT16 or FAT32) is determined by the width of the cluster entries in the FAT. Specific threshold values for the amount of clusters[7] (as stored in the BPB) have been defined to determine which FAT type is used. Even though other properties such as the size of the volume, the count of sectors, the BPB format, the file system name in an EBPB, or -in case of partitioned media- the used partition ID may often seem to be well-suited distinguishing criteria as well, they cannot reliably be used to derive the file system type from in all scenarios.[7] Whilst uncommon, it is technically possible to define a FAT12 or FAT16 volume using a "FAT32 EBPB" (which is sort of a misnomer for the EBPB variant introduced with DOS 7.1), which is normally used for FAT32 volumes, only.[nb 2] Also, while partition IDs sometimes indicate special properties such as hidden, secure, CHS or LBA access to an operating system, and as such are often used in conjunction with particular file system variants only, they are typically not used to specify a type of file system by themselves, but rather to keep (older or foreign) operating systems not aware of a partition ID from accessing partitions they cannot handle or should not work with.[12] It is therefore necessary to distinguish generic FAT file system types such as FAT12, FAT16 or FAT32 from FAT partition types such as FAT12, FAT16, FAT16B, FAT16X, FAT32, FAT32X etc.

In order to be technically correct and exact, this article uses standard prefixes for the byte unit: 1000 bytes (103 bytes) are 1 kB (kilobyte) and 1024 bytes (210 bytes) equal 1 KiB (kibibyte) etc.

Types[edit]

Original 8-bit FAT[edit]

8-bit FAT
Developer Microsoft, NCR, SCP
Full name 8-bit File Allocation Table
Introduced 1977/1978: NCR Basic +6 for NCR
1978: Standalone Disk BASIC-80 (16-byte directory entries)[13][14]
(1978: Standalone Disk BASIC-86 internal only)
1979-06-04: Standalone Disk BASIC-86 for SCP (16-byte directory entries)
1979: MIDAS (32-byte directory entries)
Limits
Max. file size limited by volume size
File size granularity record-granularity (128 bytes)[13][14]
Max. filename length 6.3 filename (binary files), 9 characters (ASCII files)[13][14]
Max. directory depth no sub-directories
Allowed characters in filenames ASCII (0x00 and 0xFF not allowed in first character)[13][14]
Features
Dates recorded No
Attributes Write protected, EBCDIC conversion, Read after write, Binary (random rather than sequential file)[13][14]

The original FAT file system (or FAT structure, as it was called initially) was designed and coded by Marc McDonald,[15] based on a series of discussions between McDonald and Bill Gates.[15] It was introduced with 8-bit table elements[13][14][15] (and valid data cluster numbers up to 0xBF[13][14]) in a precursor to Microsoft's Standalone Disk BASIC-80 for an 8080-based successor[nb 3] of the NCR 7200 model VI data-entry terminal, equipped with 8-inch (200 mm) floppy disks, in 1977[16]/1978.[nb 3] In 1978, Standalone Disk BASIC-80 was ported to the 8086 using an emulator on a DEC PDP-10,[17] since no real 8086 systems were available at this time. The FAT file system was also utilized in Microsoft's MDOS/MIDAS,[15] an operating system for 8080/Z80 platforms written by McDonald since 1979. The Standalone Disk BASIC version supported three FATs,[13][14][18] whereas this was a parameter for MIDAS. Reportedly, MIDAS was also prepared to support 10-bit, 12-bit and 16-bit FAT variants. While the size of directory entries was 16 bytes in Standalone Disk BASIC,[13][14] MIDAS instead occupied 32 bytes per entry.

Tim Paterson of Seattle Computer Products (SCP) was first introduced to Microsoft's FAT structure when he helped Bob O'Rear adapting the Standalone Disk BASIC-86 emulator port onto SCP's S-100 bus 8086 CPU board prototype during a guest week at Microsoft in May 1979.[17] The final product was shown at Lifeboat Associates' booth stand at the National Computer Conference in New York[17] on 4–7 June 1979, where Paterson learned about the more sophisticated FAT implementation in MDOS/MIDAS[15] and McDonald talked to him about the design of the file system.[16]

FAT12[edit]

FAT12
Developer SCP, Microsoft, IBM, Digital Research, Novell
Full name 12-bit File Allocation Table
Introduced 1980-07 (QDOS 0.10, 16-byte directory entries)
1981-02-25 (86-DOS 0.42, 32-byte directory entries, several reserved sectors)
ca. 1981-08/10 (PC DOS 1.0, 32-byte directory entries, 1 reserved sector)
1982-03-03 (MS-DOS 1.25, 32-byte directory entries, 1 reserved sector)
Partition identifier MBR/EBR:
FAT120x01 H:0x11/0x8D S:0xC1/0xD1
BDP: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Limits
Max. volume size 16 MiB (with 4 KiB clusters)
32 MiB (with 8 KiB clusters)
Max. file size limited by volume size
File size granularity 1 byte
Max. number of files 4,068 for 8 KiB clusters
Max. filename length 8.3 filename with OEM characters,
255 UCS-2 characters when using LFN
Max. directory depth 32 levels or 66 characters (with CDS),
60 levels or more (without CDS)
Features
Dates recorded Modified date (not with 86-DOS before 0.42), modified time (not with PC DOS 1.0 and 86-DOS), creation date/time (DOS 7.0 and higher only), access date (only available with ACCDATE enabled),[3] deletion date/time (only with DELWATCH 2)
Date range 1980-01-01 to 2099-12-31 (2107-12-31)
Date resolution 2 seconds for last modified time,
10 ms for creation time,
1 day for access date,
2 seconds for deletion time
Attributes Read-only (since DOS 2.0), Hidden, System, Volume (since MS-DOS 1.28 and PC DOS 2.0), Directory (since MS-DOS 1.40 and PC DOS 2.0), Archive (since DOS 2.0)
File system permissions File, directory and volume access rights for Read, Write, Execute, Delete only with DR-DOS, PalmDOS, Novell DOS, OpenDOS, FlexOS, 4680 OS, 4690 OS, Concurrent DOS, Multiuser DOS, System Manager, REAL/32 (Execute right only with FlexOS, 4680 OS, 4690 OS; individual file / directory passwords not with FlexOS, 4680 OS, 4690 OS; World/Group/Owner permission classes only with multiuser security loaded)
Transparent compression Per-volume, SuperStor, Stacker, DoubleSpace, DriveSpace
Transparent encryption Per-volume only with DR-DOS

Between April and August 1980, while borrowing the FAT concept for SCP's own 8086 operating system QDOS 0.10,[17] Tim Paterson extended the table elements to 12 bits,[19] reduced the number of FATs to two, redefined the semantics of some of the reserved cluster values, and modified the disk layout, so that the root directory was now located between the FAT and the data area for his implementation of FAT12. Paterson also increased the nine-character (6.3) filename[13][14] length limit to eleven characters in order to support CP/M-style 8.3 filenames and File Control Blocks. The format used in Microsoft Standalone Disk BASIC's 8-bit file system precursor was not supported by QDOS. By August 1980, QDOS had been renamed into 86-DOS already.[20] Starting with 86-DOS 0.42, the size and layout of directory entries was changed from 16 bytes to 32 bytes[21] in order to add a file date stamp[21] and increase the theoretical file size limit beyond the previous limit of 16 MiB.[21] 86-DOS 1.00 became available in early 1981. Later in 1981, 86-DOS evolved into Microsoft's MS-DOS and IBM PC DOS.[15][19][22] The capability to read previously formatted volumes with 16-byte directory entries[21] was dropped with MS-DOS 1.20.

Originally designed as a file system for floppy disks, FAT12 used 12-bit entries for the cluster addresses in the FAT, which not only limited the maximum generally possible count of data clusters to 4078 (for data clusters 0x002 to 0xFEF)[23][24] or in some controlled scenarios even up to 4084 (for data clusters 0x002 to 0xFF5),[7][8][25] but made FAT manipulation tricky with the PC's 8-bit and 16-bit registers. (While MS-DOS and PC DOS support up to 4084 data clusters on FAT12 volumes in general, cluster value 0xFF0[nb 4] is treated as additional end-of-chain marker on any FAT12 volume[12] since MS-DOS/PC DOS 3.3, which also introduced the 0xF0 media descriptor value, therefore restricting the maximum practical number of data clusters to 4078 for compatibility purposes with these operating systems.)

The disk's size was stored and calculated as a 16-bit count of sectors, which limited the size to 32 MiB for a logical sector size of 512 bytes. FAT12 was used by several manufacturers with different physical formats, but a typical floppy disk at the time was 5.25-inch (130 mm), single-sided, 40 tracks, with 8 sectors per track, resulting in a capacity of 160 KiB for both the system areas and files. The FAT12 limitations exceeded this capacity by a factor of ten or more. (NB. The 32 MiB limit was later circumvented using logical sectored FATs with logical sector sizes larger than 512 bytes in some OEM versions of MS-DOS 3.x, but this fell into disuse when FAT16B became available with DOS 3.31, which supported 32-bit sector numbers and thereby further lifted the limits.)

By convention, all the control structures were organized to fit inside the first track, thus avoiding head movement during read and write operations, although this varied depending on the manufacturer and physical format of the disk. A limitation which was not addressed until much later (with FAT32) was that any bad sector in the control structures area, track 0, could prevent the disk from being usable. The DOS formatting tool rejected such disks completely. Bad sectors were allowed only in the file data area and (since DOS 2.0) were marked with the reserved value 0xFF7 in the FAT. They made the entire containing cluster unusable.

While 86-DOS supported three disk formats (250.25 KiB, 616 KiB and 1232 KiB with FAT IDs 0xFF and 0xFE) on 8-inch (200 mm) floppy drives, IBM PC DOS 1.0, released with the original IBM Personal Computer in 1981, supported only an 8-sector floppy format with a formatted capacity of 160 KiB (FAT ID 0xFE) for single-sided 5.25-inch floppy drives, and PC DOS 1.1 added support for a double-sided format with 320 KiB (FAT ID 0xFF). PC DOS 2.0 introduced support for 9-sector floppy formats with 180 KiB (FAT ID 0xFC) and 360 KiB (FAT ID 0xFD).

86-DOS 1.00 and PC DOS 1.0 directory entries included only one date, the last modified date. PC DOS 1.1 added the last modified time. PC DOS 1.x file attributes included a hidden bit and system bit, with the remaining six bits undefined. At this time, DOS did not support a hierarchical file system, which was still acceptable, given that the number of files on a disk was typically not more than a few dozen.

The PC XT was the first PC with a hard drive from IBM, and PC DOS 2.0 supported that hard drive with FAT12 (FAT ID 0xF8). The fixed assumption of 8 sectors per clusters on hard disks practically limited the maximum partition size to 16 MiB for 512 byte sectors and 4 KiB clusters.

The BIOS Parameter Block (BPB) was introduced with PC DOS 2.0 as well, and this version also added read-only, archive, volume label, and directory attribute bits for hierarchical sub-directories.[26]

MS-DOS 3.0 introduced support for high-density 1.2 MiB 5.25-inch diskettes (media descriptor 0xF9), which notably had 15 sectors per track, hence more space for the FATs.

FAT12 remains in use on all common floppy disks, including 1.44 MiB and later 2.88 MiB disks (media descriptor byte 0xF0).

Initial FAT16[edit]

FAT16
Developer Microsoft, IBM, Digital Research, Novell
Full name 16-bit File Allocation Table
(with 16-bit sector entries)
Introduced 1984-08-14 (PC DOS 3.0)
1984-08 (MS-DOS 3.0)
Partition identifier MBR/EBR:
FAT160x04 H:0x14/0x90 S:0xC4/0xD4
BDP: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Limits
Max. file size limited by volume size
File size granularity 1 byte
Max. number of files 65,536 for 32 KiB clusters
Max. filename length 8.3 filename with OEM characters,
255 UCS-2 characters when using LFN
Max. directory depth 32 levels or 66 characters (with CDS),
60 levels or more (without CDS)
Features
Dates recorded Modified date/time, creation date/time (DOS 7.0 and higher only), access date (only available with ACCDATE enabled),[3] deletion date/time (only with DELWATCH 2)
Date range 1980-01-01 to 2099-12-31 (2107-12-31)
Date resolution 2 seconds for last modified time,
10 ms for creation time,
1 day for access date,
2 seconds for deletion time
Attributes Read-only, Hidden, System, Volume, Directory, Archive
File system permissions File, directory and volume access rights for Read, Write, Execute, Delete only with DR-DOS, PalmDOS, Novell DOS, OpenDOS, FlexOS, 4680 OS, 4690 OS, Concurrent DOS, Multiuser DOS, System Manager, REAL/32 (Execute right only with FlexOS, 4680 OS, 4690 OS; individual file / directory passwords not with FlexOS, 4680 OS, 4690 OS; World/Group/Owner permission classes only with multiuser security loaded)
Transparent compression Per-volume, SuperStor, Stacker, DoubleSpace, DriveSpace
Transparent encryption Per-volume only with DR-DOS

On 14 August 1984, IBM released the PC AT, which featured a 20 MiB hard disk and PC DOS 3.0.[27][28] Microsoft introduced MS-DOS 3.0 in parallel. Cluster addresses were increased to 16-bit, allowing for up to 65,524 clusters per volume, and consequently much greater file system sizes, at least in theory. However, the maximum possible number of sectors and the maximum (partition, rather than disk) size of 32 MiB did not change. Therefore, although cluster addresses were 16 bits, this format was not what today is commonly understood as FAT16. A partition type 0x04 indicates this form of FAT16 with less than 65536 sectors (less than 32 MiB for sector size 512).

With the initial implementation of FAT16 not actually providing for larger partition sizes than FAT12, the early benefit of FAT16 was to enable the use of smaller clusters, making disk usage more efficient, particularly for large numbers of files only a few hundred bytes in size.

MS-DOS 2.x hard disks larger than 15 MiB are incompatible with later versions of MS-DOS.[29] A 20 MiB hard disk formatted under MS-DOS 3.0 was not accessible by the older MS-DOS 2.0 because MS-DOS 2.0 did not support version 3.0's FAT16. MS-DOS 3.0 could still access MS-DOS 2.0 style 8 KiB-cluster partitions under 15 MiB.

Logical sectored FAT[edit]

When hard disks grew larger and the FAT12 and FAT16 file system implementation in MS-DOS / PC DOS did not provide means to take advantage of the extra storage, several manufacturers developed their own FAT variants to address the problem in their MS-DOS OEM issues.

Some vendors (AST and NEC) supported eight, instead of the standard four, primary partition entries in their custom extended Master Boot Record (MBR), and they adapted MS-DOS to use more than a single primary partition.

Other vendors worked around the volume size limits imposed by the 16-bit sector entries and arithmetics by increasing the size of the sectors the file system dealt with, thereby blowing up dimensions.

These so-called logical sectors were larger (up to 8192 bytes) than the physical sector size (still typically 512 bytes) as expected by the ROM-BIOS INT 13h or the disk drive hardware. The DOS-BIOS or System BIOS would then combine multiple physical sectors into logical sectors for the file system to work with. These changes were transparent to the file system implementation in the DOS kernel, since on the file system's abstraction level volumes are seen as a linear series of logically addressable sectors, also known as absolute sectors (addressed by their Logical Sector Number (LSN), starting with LSN 0) independent of the physical location of the volume on the physical medium and its geometry. The underlying DOS-BIOS translated these logical sectors into physical sectors according to partitioning information and the drive's physical geometry.

The drawback of this approach was a less memory-efficient sector buffering and deblocking in the DOS-BIOS, thereby causing an increased memory footprint for the DOS data structures. Since older DOS versions were not flexible enough to work with these logical geometries, the OEMs had to introduce new partition IDs for their FAT variants in order to hide them from off-the-shelf issues of MS-DOS and PC DOS. Known partition IDs for logical sectored FATs include: 0x08 (Commodore MS-DOS 3.x), 0x11 (Leading Edge MS-DOS 3.x), 0x14 (AST MS-DOS 3.x), 0x24 (NEC MS-DOS 3.30), 0x56 (AT&T MS-DOS 3.x), 0xE5 (Tandy MS-DOS), 0xF2 (Sperry IT MS-DOS 3.x, Unisys MS-DOS 3.3 — also used by Digital Research DOS Plus 2.1).[30] OEM versions like Toshiba MS-DOS, Wyse MS-DOS 3.2 and 3.3,[31] as well as Zenith MS-DOS are also known to have utilized logical sectoring.[32]

While non-standard and sub-optimal, these FAT variants are perfectly valid according to the specifications of the file system itself. Therefore, even if default issues of MS-DOS and PC DOS were not able to cope with them, most of these vendor-specific FAT12 and FAT16 variants can be mounted by more flexible file system implementations in operating systems such as DR-DOS, simply by changing the partition ID to one of the recognized types.[nb 5] Also, if they no longer need to be recognized by their original operating systems, existing partitions can be "converted" into FAT12 and FAT16 volumes more compliant with versions of MS-DOS/PC DOS 4.0-6.3, which do not support sector sizes different from 512 bytes,[33] by switching to a BPB with 32-bit entry for the number of sectors, as introduced since DOS 3.31 (see FAT16B below), keeping the cluster size and reducing the logical sector size in the BPB down to 512 bytes, while at the same time increasing the counts of logical sectors per cluster, reserved logical sectors, total logical sectors, and logical sectors per FAT by the same factor.

A parallel development in MS-DOS / PC DOS which allowed an increase in the maximum possible FAT size was the introduction of multiple FAT partitions on a hard disk. To allow the use of more FAT partitions in a compatible way, a new partition type was introduced in PC DOS 3.2 (1986), the extended partition (EBR),[15] which is a container for an additional partition called logical drive. Since PC DOS 3.3 (April 1987), there is another, optional extended partition containing the next logical drive, and so on. The MBR of a hard disk can either define up to four primary partitions, or an extended partition in addition to up to three primary partitions.

Final FAT16[edit]

FAT16B
Developer Compaq, Digital Research, IBM, Microsoft, Novell
Full name 16-bit File Allocation Table
(with 32-bit sector entries)
Introduced 1987-11 (Compaq MS-DOS 3.31)
1988-06-28 (DR DOS 3.31)
1988 (IBM DOS 4.0)
1988 (OS/2 1.1)
1988 (MS-DOS 4.0)
Partition identifier MBR/EBR:
FAT16B0x06 H:0x16/0x92 S:0xC6/0xD6
FAT16X: 0x0E H:0x1E/0x9A S:0xCE
FAT16+: 0x28 S:0xC8
BDP: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Limits
Min. volume size MiB (with 128 byte sectors)
32 MiB (with 512 byte sectors)
256 MiB (with KiB sectors)
Max. volume size GiB (with 32 KiB clusters)
GiB (with 64 KiB clusters) (NT 4, PTS-DOS, EDR-DOS)
GiB (with 128 KiB clusters and 1 or 2 KiB sectors) (NT 4 and EDR-DOS only)
GiB (with 128 KiB clusters and 512 byte sectors) (EDR-DOS only)
16 GiB (with 256 KiB clusters and 2 or 4 KiB sectors) (NT 4 only)
Max. file size 2,147,483,647 bytes (2 GiB - 1) (without LFS)
4,294,967,295 bytes (4 GiB - 1) (with LFS)
limited by volume size only (with FAT16+[2])
File size granularity 1 byte
Max. number of files 65,460 for 32 KiB clusters
Max. filename length 8.3 filename with OEM characters,
255 UCS-2 characters when using LFN
Max. directory depth 32 levels or 66 characters (with CDS),
60 levels or more (without CDS)
Features
Dates recorded Modified date/time, creation date/time (DOS 7.0 and higher only), access date (only available with ACCDATE enabled),[3] deletion date/time (only with DELWATCH 2)
Date range 1980-01-01 to 2099-12-31 (2107-12-31)
Date resolution 2 seconds for last modified time,
10 ms for creation time,
1 day for access date,
2 seconds for deletion time
Attributes Read-only, Hidden, System, Volume, Directory, Archive
File system permissions File, directory and volume access rights for Read, Write, Execute, Delete only with DR-DOS, PalmDOS, Novell DOS, OpenDOS, FlexOS, 4680 OS, 4690 OS, Concurrent DOS, Multiuser DOS, System Manager, REAL/32 (Execute right only with FlexOS, 4680 OS, 4690 OS; individual file / directory passwords not with FlexOS, 4680 OS, 4690 OS; World/Group/Owner permission classes only with multiuser security loaded)
Transparent compression Per-volume, SuperStor, Stacker, DoubleSpace, DriveSpace
Transparent encryption Per-volume only with DR-DOS

In November 1987, Compaq MS-DOS 3.31 (a modified OEM version of MS-DOS 3.3 released by Compaq with their machines) introduced what today is simply known as the FAT16 format, with the expansion of the 16-bit disk sector count to 32 bits in the BPB. Although the on-disk changes were minor, the entire DOS disk driver had to be converted to use 32-bit sector numbers, a task complicated by the fact that it was written in 16-bit assembly language. The result was initially called the DOS 3.31 Large File System. Microsoft's DSKPROBE tool refers to type 0x06 as BigFAT,[34] whereas some older versions of FDISK described it as BIGDOS. Technically, it is known as FAT16B.

Since older versions of DOS were not designed to cope with more than 65535 sectors, it was necessary to introduce a new partition type for this format in order to hide it from pre-3.31 issues of DOS. The original form of FAT16 (with less than 65536 sectors) had a partition type 0x04. To deal with disks larger than this, type 0x06 was introduced to indicate 65536 or more sectors. In addition to this, the disk driver was expanded to cope with more than 65535 sectors as well. The only other difference between the original FAT16 and the newer FAT16B format is the usage of a newer BPB format with 32-bit sector entry. Therefore, newer operating systems supporting the FAT16B format can cope also with the original FAT16 format without any necessary changes.

If partitions to be used by pre-DOS 3.31 issues of DOS need to be created by modern tools, the only criteria theoretically necessary to meet are a sector count of less than 65536, and the usage of the old partition ID (0x04). In practice however, type 0x01 and 0x04 primary partitions should not be physically located outside the first 32 MiB of the disk, due to other restrictions in MS-DOS 2.x, which could not cope with them otherwise.

In 1988, the FAT16B improvement became more generally available through DR DOS 3.31, PC DOS 4.0, OS/2 1.1, and MS-DOS 4.0. The limit on partition size was dictated by the 8-bit signed count of sectors per cluster, which originally had a maximum power-of-two value of 64. With the standard hard disk sector size of 512 bytes, this gives a maximum of 32 KiB cluster size, thereby fixing the "definitive" limit for the FAT16 partition size at 2 GiB for sector size 512. On magneto-optical media, which can have 1 or 2 KiB sectors instead of 0.5 KiB, this size limit is proportionally larger.

Much later, Windows NT increased the maximum cluster size to 64 KiB, by considering the sectors-per-cluster count as unsigned. However, the resulting format was not compatible with any other FAT implementation of the time, and it generated greater internal fragmentation. Windows 98, SE and ME also supported reading and writing this variant, but its disk utilities did not work with it and some FCB services are not available for such volumes. This contributes to a confusing compatibility situation.

Prior to 1995, versions of DOS accessed the disk via CHS addressing only. When MS-DOS 7.0 / Windows 95 introduced LBA disk access, partitions could start being physically located outside the first ca. 8 GiB of this disk and thereby out of the reach of the traditional CHS addressing scheme. Partitions partially or fully located beyond the CHS barrier therefore had to be hidden from non-LBA-enabled operating systems by using the new partition type 0x0E in the partition table instead. FAT16 partitions using this partition type are also named FAT16X.[35] The only difference, compared to previous FAT16 partitions, is the fact that some CHS-related geometry entries in the BPB record, namely the number of sectors per track and the number of heads, may contain no or misleading values and should not be used.

The number of root directory entries available for FAT12 and FAT16 is determined when the volume is formatted, and is stored in a 16-bit field. For a given number RDE and sector size SS, the number RDS of root directory sectors is RDS=ceil((RDE×32)/SS), and RDE is normally chosen to fill these sectors, i.e., RDE*32=RDS*SS. FAT12 and FAT16 media typically use 512 root directory entries on non-floppy media. Some third-party tools, like mkdosfs, allow the user to set this parameter.[36]

FAT32[edit]

FAT32
Developer Microsoft, Caldera
Full name 32-bit File Allocation Table
(with 28-bit cluster entries)
Introduced 1996-08 (Windows 95 OSR2)
Partition identifier MBR/EBR:
FAT32: 0x0B H:0x1B/0x97 S:0xCB
FAT32X: 0x0C H:0x1C/0x98 S:0xCC
FAT32+: 0x29 S:0xC9
BDP: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Limits
Min. volume size 32 MiB-4.5 KiB (with 65525 clusters and 512 byte sectors)
256 MiB-36 KiB (with 65525 clusters and KiB sectors)
Max. volume size TiB (with 512 byte sectors)
TiB (with 2 KiB sectors and 32 KiB clusters)
16 TiB (with 4 KiB sectors and 64 KiB clusters)
Max. file size 2,147,483,647 bytes (2 GiB - 1) (without LFS)
4,294,967,295 bytes (4 GiB - 1)[1] (with LFS)
274,877,906,943 bytes (256 GiB - 1) (only with FAT32+[2])
File size granularity 1 byte
Max. number of files 268,173,300 for 32 KiB clusters
Max. filename length 8.3 filename with OEM characters,
255 UCS-2 characters when using LFN
Max. directory depth 32 levels or 66 characters (with CDS),
60 levels or more (without CDS)
Features
Dates recorded Modified date/time, creation date/time (DOS 7.0 and higher only), access date (only available with ACCDATE enabled),[3] deletion date/time (only with DELWATCH 2)
Date range 1980-01-01 to 2099-12-31 (2107-12-31)
Date resolution 2 seconds for last modified time,
10 ms for creation time,
1 day for access date,
2 seconds for deletion time
Attributes Read-only, Hidden, System, Volume, Directory, Archive
File system permissions Partial, only with DR-DOS, REAL/32 and 4690 OS
Transparent compression No
Transparent encryption No

In order to overcome the volume size limit of FAT16, while at the same time allowing DOS real mode code to handle the format, Microsoft designed a new version of the file system, FAT32, which supported an increased number of possible clusters, but could reuse most of the existing code, so that the available conventional memory footprint was reduced by less than 5 KiB under DOS.[37] Cluster values are represented by 32-bit numbers, of which 28 bits are used to hold the cluster number. The boot sector uses a 32-bit field for the sector count, limiting the FAT32 volume size to 2 TiB for a sector size of 512 bytes and 16 TiB for a sector size of 4,096 bytes.[38][39] FAT32 was introduced with MS-DOS 7.1 / Windows 95 OSR2 in 1996, 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 Windows NT line, native support for FAT32 arrived in Windows 2000. A free FAT32 driver for Windows NT 4.0 was available from Winternals, a company later acquired by Microsoft. Since the acquisition the driver is no longer officially available. Since 1998, Caldera's dynamically loadable DRFAT32 driver could be used to enable FAT32 support in DR-DOS. The first version of DR-DOS to natively support FAT32 and LBA access was OEM DR-DOS 7.04 in 1999. That same year IMS introduced native FAT32 support with REAL/32 7.90, and IBM 4690 OS added FAT32 support with version 2.[40] Ahead Software provided another dynamically loadable FAT32.EXE driver for DR-DOS 7.03 with Nero Burning ROM in 2004. IBM PC DOS introduced native FAT32 support with OEM PC DOS 7.10 in 2003.

The maximum possible size for a file on a FAT32 volume is 4 GiB minus 1 byte or 4,294,967,295 (232 − 1) bytes. This limit is a consequence of the file length entry in the directory table and would also affect huge FAT16 partitions with a sufficient sector size.[1] Video applications, DVD images, large databases, and some other software easily exceed this limit.

The open FAT+[2] specification proposes how to store larger files up to 256 GiB minus 1 byte or 274,877,906,943 (238 − 1) bytes on slightly modified and otherwise backwards compatible FAT32 volumes, but imposes a risk that disk tools or FAT32 implementations not aware of this extension may truncate or delete files exceeding the normal FAT32 file size limit. Also, support for FAT32+ (and FAT16+) is limited to some versions of DR-DOS and not available in mainstream operating systems so far. (This extension is critically incompatible with the /EAS option of the FAT32.IFS method to store OS/2 extended attributes on FAT32 volumes.)

As with previous file systems, the design of the FAT32 file system does not include direct built-in support for long filenames, but FAT32 volumes can optionally hold VFAT long filenames in addition to short filenames in exactly the same way as VFAT long filenames have been optionally implemented for FAT12 and FAT16 volumes.

Two partition types have been reserved for FAT32 partitions, 0x0B and 0x0C. The latter type is also named FAT32X in order to indicate usage of LBA disk access instead of CHS. On such partitions, some CHS-related geometry entries in the EBPB record, namely the number of sectors per track and the number of heads, may contain no or misleading values and should not be used.

Extensions[edit]

Extended Attributes[edit]

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 two previously reserved bytes in the file's (or directory's) directory entry at offset 0x14.[41] In the FAT32 format, these bytes hold the upper 16 bits of the starting cluster number of the file or directory, hence making it impossible to store OS/2 EAs on FAT32 using this method.

However, the third-party FAT32 installable file system (IFS) driver FAT32.IFS version 0.70 and higher by Henk Kelder & Netlabs for OS/2 and eComStation stores extended attributes in extra files with filenames having the string "␠EA.␠SF" appended to the regular filename of the file to which they belong. The driver also utilizes the byte at offset 0x0C in directory entries to store a special mark byte indicating the presence of extended attributes to help speed up things.[42][43] (This extension is critically incompatible with the FAT32+ method to store files larger than 4 GiB minus 1 on FAT32 volumes.[2])

Extended attributes are accessible via the Workplace Shell desktop, through REXX scripts, and many system GUI and command-line utilities (such as 4OS2).[44]

To accommodate its OS/2 subsystem, Windows NT supports the handling of extended attributes in HPFS, NTFS, FAT12 and FAT16. It stores EAs on FAT12, FAT16 and HPFS using exactly the same scheme as OS/2, but does not support any other kind 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 or HPFS volume gives a warning message with the names of the ADSs that will be lost. It does not support the FAT32.IFS method to store EAs on FAT32 volumes.

Windows 2000 onward acts exactly as Windows NT, except that it ignores EAs when copying to FAT32 without any warning (but shows the warning for other ADSs, like "Macintosh Finder Info" and "Macintosh Resource Fork").

Cygwin uses "EA␠DATA.␠SF" files as well.

Long file names[edit]

One of the user experience goals for the designers of Windows 95 was the ability to use long filenames (LFNs—up to 255 UCS-2 code units long), in addition to classic 8.3 filenames (SFNs). For backward and forward compatibility LFNs were implemented as an optional extension on top of the existing FAT file system structures using a workaround in the way directory entries are laid out.

This transparent method to store long file names in the existing FAT file systems without altering their data structures is usually known as VFAT (for "Virtual FAT") after the Windows 95 virtual device driver.[nb 1]

Non VFAT-enabled operating systems can still access the files under their short file name alias without restrictions, however, the associated long file names may get lost, when files with long file names are copied under non VFAT-aware operating systems.

In Windows NT, support for VFAT long filenames started from version 3.5.

Linux provides a VFAT filesystem driver to work with FAT volumes with VFAT long filenames. For some while, a UVFAT driver was available to provide combined support for UMSDOS-style permissions with VFAT long filenames.

OS/2 added long filename support to FAT using extended attributes (EA) before the introduction of VFAT; thus, VFAT long filenames are invisible to OS/2, and EA long filenames are invisible to Windows, therefore experienced users of both operating systems would have to manually rename the files.

In order to support Java applications, the FlexOS-based IBM 4690 OS version 2 introduced its own virtual file system (VFS) architecture to store long filenames in the FAT file system in a backwards compatible fashion. If enabled, the virtual filenames (VFN) are available under separate logical drive letters, whereas the real filenames (RFN) remain available under the original drive letters.[45]

Forks and Alternate Data Streams[edit]

The FAT file system itself is not designed for supporting Alternate Data Streams (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).

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 X stores resource forks and metadata (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".

UMSDOS permissions and filenames[edit]

Further information: FAT filesystem and Linux

Early Linux distributions also supported a format known as UMSDOS, a FAT variant with Unix file attributes (such as long file name and access permissions) stored in a separate file called "--linux-.---". UMSDOS fell into disuse after VFAT was released and it is not enabled by default in Linux kernels from version 2.5.7 onwards.[46] For some time, Linux also provided combined support for UMSDOS-style permissions and VFAT long filenames through UVFAT.

Derivatives[edit]

Turbo FAT[edit]

Main article: Turbo FAT

In its NetWare File System (NWFS) Novell implemented a heavily modified variant of a FAT file system for the NetWare operating system. For larger files it utilized a performance feature named Turbo FAT.

FATX[edit]

FATX is a family of file systems designed for Microsoft's Xbox video game console hard disk drives and memory cards,[47][48] introduced in 2001.

While resembling the same basic design ideas as FAT16 and FAT32, the FATX16 and FATX32 on-disk structures are simplified but fundamentally incompatible with normal FAT16 and FAT32 file systems, making it impossible for normal FAT file system drivers to mount such volumes.

The non-bootable superblock sector is 4 KiB in size and holds an 18 byte large BPB-like structure completely different from normal BPBs. Clusters are typically 16 KiB in size and there is only one copy of the FAT on the Xbox. Directory entries are 64 bytes in size instead of the normal 32 bytes. Files can have filenames up to 42 characters long using the OEM character set and be up to 4 GiB minus 1 byte in size. The on-disk timestamps hold creation, modification and access dates and times but differ from FAT: in FAT, the epoch is 1980; in FATX, the epoch is 2000.[citation needed] On the Xbox 360, the epoch is 1980.[49]

exFAT[edit]

Main article: exFAT

exFAT is a file system introduced with Windows Embedded CE 6.0 in November 2006 and brought to the Windows NT family with Vista Service Pack 1. It is loosely based on the File Allocation Table architecture, but incompatible, proprietary and protected by patents. Microsoft's GUI and command-line format utilities offer it as an alternative to NTFS (and, for smaller partitions, to FAT16B and FAT32).

exFAT is intended for use on flash drives (such as SDXC and Memory Stick XC), where FAT32 is otherwise used.

Storage devices formatted as exFAT cannot exchange data with equipment not supporting the format. Most consumer electronics do not support exFAT, which requires acquisition of a commercial license from Microsoft,[50] which rules out its legal distribution as part of open source operating systems.

exFAT offers several benefits over FAT32 including breaking the 4 GiB file size limit of standard FAT32 (contrast FAT32+ above), being more space-efficient for files smaller than 64 KiB on large volumes and, compared to light-weight implementations of FAT32 in DOS and some embedded systems, it can offer faster seeks if more than a few thousand files are stored in a single sub-directory, whereas FAT32 is typically faster than exFAT for larger and unfragmented files as used on digital cameras, camcorders and media players or when flash cards are used mainly for archival purposes.[citation needed]

The MBR partition type is 0x07 (the same as used for IFS, HPFS, NTFS, etc.). Logical geometry information located in the VBR is stored in a format not resembling any kind of BPB.

Patents[edit]

Microsoft applied for, and was granted, a series of patents for key parts of the FAT file system in the mid-1990s. All four pertain to long-filename extensions to FAT first seen in Windows 95: U.S. Patent 5,579,517, U.S. Patent 5,745,902, U.S. Patent 5,758,352, U.S. Patent 6,286,013.

On December 3, 2003 Microsoft announced[51] that 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.[52] To this end, Microsoft cited four patents on the FAT file system as the basis of its intellectual property claims.

In the EFI FAT32 specification[7] Microsoft specifically grants a number of rights, which many readers have interpreted as permitting operating system vendors to implement FAT.[53]

Non-Microsoft patents affecting FAT include: U.S. Patent 5,367,671, specific to the OS/2 extended object attributes (expired in 2011).

Challenges and lawsuits[edit]

The Public Patent Foundation (PUBPAT) submitted evidence to the US Patent and Trade Office (USPTO) in 2004 disputing the validity of U.S. Patent 5,579,517, including prior art references from Xerox and IBM.[54] The USPTO opened an investigation and concluded by rejecting all claims.[55] The next year, the USPTO further announced that following the re-examination process, it affirmed the rejection of '517 and additionally found U.S. Patent 5,758,352 invalid on the grounds that the patent had incorrect assignees.

However, in 2006 the USPTO ruled that features of Microsoft's implementation of the FAT system were "novel and non-obvious", reversing both earlier decisions and leaving the patents valid.[56]

In February 2009, Microsoft filed a patent infringement lawsuit against TomTom alleging that the device maker's products infringe on patents related to VFAT long filenames. As some TomTom products are based on Linux, this marked the first time that Microsoft tried to enforce its patents against the Linux platform.[57] The lawsuit was settled out of court the following month with an agreement that Microsoft be given access to four of TomTom's patents, that TomTom will drop support for the VFAT long filenames from its products, and that in return Microsoft not seek legal action against TomTom for the five year duration of the settlement agreement.[58]

In October 2010, Microsoft filed a patent infringement lawsuit against Motorola alleging several patents (including two of the VFAT patents) were not licensed for use in the Android operating system.[59] They also submitted a complaint to the ITC.[60] Developers of open source software have designed methods intended to circumvent Microsoft's patents.[61][62]

In 2013, patent EP0618540 "common name space for long and short filenames" was invalidated in Germany.[63]

See also[edit]

Notes[edit]

  1. ^ a b A driver named VFAT appeared before Windows 95, in Windows for Workgroups 3.11, but this older version was only used for implementing 32-bit file access and did not support long file names.
  2. ^ Windows XP has been observed to create similar 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.)
  3. ^ a b Sources differ in regard to the first NCR data entry terminal integrating support for the FAT file system. According to Stephen Manes and Paul Andrews, "Gates", development was for a NCR 8200 in late 1977, incorrectly classified as a floppy-based upgrade to the NCR 7200, which had been released in 1975-11 (model I and IV) and was built around an Intel 8080 8-bit processor, but was cassette-based only. However, the NCR Century 8200 was a 16-bit minicomputer, onto which several data entry terminals could be hooked up. Marc McDonald even remembered a NCR 8500, a mainframe of the Criterion series, which can be ruled out as well. Announced 1977-10 for shipment in 1978-02, NCR also introduced the NCR I-8100 series including the 8080-based NCR I-8130 and NCR I-8150 models of small business systems featuring dual floppy disks. Other sources indicate that either the NCR 7200 series itself or the successor series were the actual target platform. NCR Basic Plus 6 (based on Microsoft Extended BASIC-80) became available for the cassette-based NCR 7200 model VI in Q1/1977. The NCR 7500 series was released in 1978, based on a similar 8080 hardware, but now including NCR 7520 and 7530 models featuring 8-inch diskettes. NCR Basic +6, a precursor or adaptation of Standalone Disk BASIC-80 was available for them at least since 1979. One source claims that a special NCR 7200 model variant with two 8-inch diskettes and Microsoft BASIC existed and was imported by NCR Sydney into Australia the least.
  4. ^ See FAT end-of-chain marker for special precautions in regard to occurrences of a cluster value of 0xFF0 on FAT12 volumes under MS-DOS/PC DOS 3.3 and higher.
  5. ^ DR-DOS is able to boot off FAT12/FAT16 logical sectored media with logical sector sizes up to 1024 bytes.

References[edit]

  1. ^ a b c "File Systems". Microsoft TechNet. 2001. Retrieved 2011-07-31. 
  2. ^ a b c d e Udo Kuhnt, Luchezar Georgiev, Jeremy Davis (2007). FAT+. FATPLUS.TXT, draft revision 2 ([1], [2]).
  3. ^ a b c d e Microsoft (2006-11-15). Windows 95 CD-ROM CONFIG.TXT File Article 135481, Revision: 1.1, retrieved 2011-12-22: "For each hard disk, specifies whether to record the date that files are last accessed. Last access dates are turned off for all drives when your computer is started in safe mode, and are not maintained for floppy disks by default. Syntax: ACCDATE=drive1+|- [drive2+|-]..."
  4. ^ a b "FAT File System (Windows Embedded CE 6.0)". Microsoft. 2010-01-06. Retrieved 2013-07-07. 
  5. ^ "Comparing NTFS and FAT file systems". Microsoft. Retrieved 2014-01-27. 
  6. ^ JEIDA/JEITA/CIPA (2010). "Standard of the Camera & Imaging Products Association, CIPA DC-009-Translation-2010, Design rule for Camera File system: DCF Version 2.0 (Edition 2010)". Retrieved 2011-04-13. 
  7. ^ a b c d e "Microsoft Extensible Firmware Initiative FAT32 File System Specification, FAT: General Overview of On-Disk Format". Microsoft. 2000-12-06. Retrieved 2011-07-03. 
  8. ^ a b "Volume and File Structure of Disk Cartridges for Information Interchange". Standard ECMA-107 (2nd ed., June 1995). ECMA. 1995. Retrieved 2011-07-30. 
  9. ^ "Information technology -- Volume and file structure of disk cartridges for information interchange". ISO/IEC 9293:1994. ISO catalogue. 1994. Retrieved 2012-01-06. 
  10. ^ "Information processing -- Volume and file structure of flexible disk cartridges for information interchange". ISO 9293:1987. ISO catalogue. 1987. Retrieved 2012-01-06. 
  11. ^ Aaron R. Reynolds, Dennis R. Adler, Ralph A. Lipe, Ray D. Pedrizetti, Jeffrey T. Parsons, Rasipuram V. Arun (1998-05-26). "Common name space for long and short filenames". US Patent 5758352. Retrieved 2012-01-19. 
  12. ^ a b Geoff Chappell (1994). DOS Internals. Addison Wesley. ISBN 0-201-60835-9, ISBN 978-0-201-60835-9.
  13. ^ a b c d e f g h i j Xerox BASIC-80 - basic-80 reference manual. 5.0. Microsoft, Xerox. 1979. 610P70641. Retrieved 2014-06-02.  (NB. For Microsoft (Standalone Disk / Disk / Extended / 8K) BASIC-80, (Standalone Disk / Extended) BASIC-86, BASIC Compiler, release 5.0)
  14. ^ a b c d e f g h i j MICROSOFT BASIC-80 version 5.0 reference manual / BASIC-80 Interpreter and Compiler Addendum Release 5.1. 5.1. Microsoft. 1979. Retrieved 2014-06-02.  (NB. For Microsoft (Standalone Disk / Disk / Extended / 8K) BASIC-80, (Standalone Disk / Extended) BASIC-86, BASIC Compiler, release 5.1)
  15. ^ a b c d e f g Ray Duncan (1988). The MS-DOS Encyclopedia - version 1.0 through 3.2. Microsoft Press. ISBN 1-55615-049-0.
  16. ^ a b Manes, Stephen; Paul Andrews (1993). Gates: How Microsoft's Mogul Reinvented an Industry—and Made Himself the Richest Man in America. Doubleday. ISBN 0-385-42075-7. 
  17. ^ a b c d Hunter, David (1983). "Tim Paterson - The roots of DOS". Softalk for the IBM Personal Computer (March 1983). Retrieved 2014-06-02. 
  18. ^ Schulman, Andrew; Brown, Ralf; Maxey, David; Michels, Raymond J.; Kyle, Jim (1994). Undocumented DOS - A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 (2 ed.). Addison Wesley. p. 11. ISBN 0-201-63287-X. ISBN 978-0-201-63287-3. 
  19. ^ a b Tim Paterson (2007-09-30). "Design of DOS". DosMan Drivel. Retrieved 2011-07-04. 
  20. ^ Seattle Computer Products (August 1980). "86-DOS - 8086 OPERATING SYSTEM - $95". Byte. 8 5. p. 174. Retrieved 2013-08-18.  (NB. The SCP advertisement already calls the product 86-DOS, but does not mention a specific version number. Version 0.3 is known to be called 86-DOS already, so the name change must have taken place either for version 0.2 or immediately afterwards in August 1980.)
  21. ^ a b c d Seattle Computer Products (1981). "SCP 86-DOS 1.0 Addendum". Retrieved 2013-03-10. 
  22. ^ Wallace & Erickson, 1992. Hard Drive. John Wiley & Sons. ISBN 0-471-56886-4.
  23. ^ Peter Norton (1986). Inside the IBM PC, Revised and Enlarged, Brady. ISBN 0-89303-583-1, p. 157.
  24. ^ Brian Jenkinson, Sammes, A. J. (2000). Forensic Computing: A Practitioner's Guide (Practitioner Series). Berlin: Springer. p. 157. ISBN 1-85233-299-9. "... only 2^12 (that is, 4096) allocation units or clusters can be addressed. In fact, the number is less than this, since 000h and 001h are not used and FF0h to FFFh are reserved or used for other purposes, leaving 002h to FEFh (2 to 4079) as the range of possible clusters." 
  25. ^ Andries Brouwer. "FAT under Linux". 
  26. ^ Tim Paterson (1983). "An Inside Look at MS-DOS". Byte. Retrieved 2011-07-18. "The numbering starts with 2; the first two numbers, 0 and 1, are reserved." 
  27. ^ IBM (1984). IBM PC DOS 3.0 announcement letter.
  28. ^ IBM (1985). IBM PC DOS Technical Reference. First Edition, P/N 6024181, dated February 1985.
  29. ^ Microsoft Knowledge Base article: "MS-DOS Partitioning Summary"
  30. ^ Andries Brouwer. "List of partition identifiers for PCs". 
  31. ^ Microsoft (2000-12-17). Wyse DOS 3.3 Partitions Incompatible with MS-DOS 5.x and 6.x. Document Q78407 ([3]).
  32. ^ Microsoft (2000-12-17). Upgrading Pre-4.0 Systems with Logical Drive(s) > 32 MB. Document Q68176 ([4]).
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