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82-466: The FAT file system is a file system used on MS-DOS and Windows 9x family of operating systems . It continues to be used on mobile devices and embedded systems , and thus is a well-suited file system for data exchange between computers and devices of almost any type and age from 1981 through to the present. A FAT file system is composed of four regions: Important information from the Boot Sector

164-543: A DOS 3.31 BPB some GPT boot loaders (like BootDuet ) use 0x1FA – 0x1FD to store the high 4 bytes of the hidden sectors for volumes located outside the first 2-1 sectors. Since this location may contain code or other data in other boot sectors, it may not be written to when 0x1F9 – 0x1FD do not all contain zero.) If this belongs to a boot volume, the DR-DOS 7.07 enhanced MBR can be configured (see NEWLDR offset 0x014 ) to dynamically update this entry to

246-559: A Y2K compliant DOS. As it reports itself as "IBM PC-DOS 7 Revision 1", it is often refereed to as "IBM PC-DOS7R1" or just "PC-DOS7R1". Hitachi used PC DOS 2000 in their legacy Drive Fitness Test (4.15) and Hitachi Feature Tool (2.15) until 2009. ThinkPad products had a copy of the latest version of PC DOS in their Rescue and Recovery partition. PC DOS 7.1 added support for Logical Block Addressing (LBA) and FAT32 partitions. Various builds from 1999 up to 2003 were not released in retail, but used in products such as

328-613: A boot sector depending on certain values detected here (e.g., NEWLDR offset 0x018 ). The boot ROM of the Wang Professional Computer will only treat a disk as bootable if the first four characters of the OEM label are " Wang ". Similarly, the ROM BIOS of the Philips :YES will only boot from a disk if the first four characters of the OEM label are " :YES ". If, in an FAT32 EBPB ,

410-424: A device, device type, directory prefix, file path separator, or file type. File systems typically support organizing files into directories , also called folders , which segregate files into groups. This may be implemented by associating the file name with an index in a table of contents or an inode in a Unix-like file system. Directory structures may be flat (i.e. linear), or allow hierarchies by allowing

492-652: A directory to contain directories, called subdirectories. The first file system to support arbitrary hierarchies of directories was used in the Multics operating system. The native file systems of Unix-like systems also support arbitrary directory hierarchies, as do, Apple 's Hierarchical File System and its successor HFS+ in classic Mac OS , the FAT file system in MS-DOS 2.0 and later versions of MS-DOS and in Microsoft Windows ,

574-505: A few glitches. Newly added EMS drivers were only compatible with IBM's EMS boards and not the more common Intel and AST ones. DOS 4.0 is also notable for including the first version of the DOS Shell , a full-screen utility designed to make the command-line OS more user-friendly. Microsoft took back control of development and released a bug-fixed DOS 4.01. DOS 5 debuted in June 1991. DOS 5 supported

656-496: A file system can be managed by the user via various utility programs. PC DOS 7.1 IBM PC DOS (an acronym for IBM Personal Computer Disk Operating System ), also known as PC DOS or IBM DOS , is a discontinued disk operating system for the IBM Personal Computer , its successors, and IBM PC compatibles . It was manufactured and sold by IBM from the early 1980s into the 2000s. Developed by Microsoft , it

738-443: A file system creates a file, it allocates space for data. Some file systems permit or require specifying an initial space allocation and subsequent incremental allocations as the file grows. To delete a file, the file system records that the file's space is free; available to use for another file. A local file system manages storage space to provide a level of reliability and efficiency. Generally, it allocates storage device space in

820-422: A file system implementation. The physical file system layer provides relatively low-level access to a storage device (e.g. disk). It reads and writes data blocks , provides buffering and other memory management and controls placement of blocks in specific locations on the storage medium. This layer uses device drivers or channel I/O to drive the storage device. A file name , or filename , identifies

902-417: A file to consuming applications and in some cases users. A file name is unique so that an application can refer to exactly one file for a particular name. If the file system supports directories, then generally file name uniqueness is enforced within the context of each directory. In other words, a storage can contain multiple files with the same name, but not in the same directory. Most file systems restrict

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984-697: A forked file system on the Macintosh, and Microsoft supports streams in NTFS. Some file systems maintain multiple past revisions of a file under a single file name; the file name by itself retrieves the most recent version, while prior saved version can be accessed using a special naming convention such as "filename;4" or "filename(-4)" to access the version four saves ago. See comparison of file systems#Metadata for details on which file systems support which kinds of metadata. A local file system tracks which areas of storage belong to which file and which are not being used. When

1066-472: A granular manner, usually multiple physical units (i.e. bytes ). For example, in Apple DOS of the early 1980s, 256-byte sectors on 140 kilobyte floppy disk used a track/sector map . The granular nature results in unused space, sometimes called slack space , for each file except for those that have the rare size that is a multiple of the granular allocation. For a 512-byte allocation, the average unused space

1148-619: A group of Microsoft programmers (primarily Paul Allen , Mark Zbikowski and Aaron Reynolds ) began work on PC DOS 2.0. Completely rewritten, DOS 2.0 added subdirectories and hard disk support for the new IBM XT , which debuted in March 1983. A new 9-sector format bumped the capacity of floppy disks to 360 KB. The Unix -inspired kernel featured file handles in place of the CP/M-derivative file control blocks and loadable device drivers could now be used for adding hardware beyond that which

1230-692: A maximum of 255 heads only. File system A file system provides a data storage service that allows applications to share mass storage . Without a file system, applications could access the storage in incompatible ways that lead to resource contention , data corruption and data loss . There are many file system designs and implementations – with various structure and features and various resulting characteristics such as speed, flexibility, security, size and more. Files systems have been developed for many types of storage devices , including hard disk drives (HDDs), solid-state drives (SSDs), magnetic tapes and optical discs . A portion of

1312-547: A multiple of 16. The maximum value supported on floppy disks is 240, the maximum value supported by MS-DOS/PC DOS on hard disks is 512. DR-DOS supports booting off FAT12/FAT16 volumes, if the boot file is located in the first 2048 root directory entries. This value must reflect the media descriptor stored (in the entry for cluster 0 ) in the first byte of each copy of the FAT. Certain operating systems before DOS 3.2 ( 86-DOS , MS-DOS / PC DOS 1.x and MSX-DOS version 1.0) ignore

1394-524: A near jump ( 0xE9 0x?? 0x?? as seen on most ( Compaq , TeleVideo ) DOS 2.x formatted disks as well as on some ( Epson , Olivetti ) DOS 3.1 disks). For backward compatibility MS-DOS, PC DOS and DR-DOS also accept a jump ( 0x69 0x?? 0x?? ) on removable disks. On hard disks, DR DOS additionally accepts the swapped JMPS sequence starting with a NOP ( 0x90 0xEB 0x?? ), whereas MS-DOS/PC DOS do not. (See below for Atari ST compatibility.) The presence of one of these opstring patterns (in combination with

1476-510: A recognized BPB format and a media descriptor of either 0xF8 or 0xFA to 0xFF MS-DOS/PC DOS treats bit 1 as a flag to choose a 9-sectors per track format rather than an 8-sectors format, and bit 0 as a flag to indicate double-sided media. Values 0x00 to 0xEF and 0xF1 to 0xF7 are reserved and must not be used. DOS 3.0 BPB: The following extensions were documented since DOS 3.0, however, they were already supported by some issues of DOS 2.11. MS-DOS 3.10 still supported

1558-520: A reversed signature 0xAA 0x55 has been observed on disk images. This can be the result of a faulty implementation in the formatting tool based on faulty documentation, but it may also indicate a swapped byte order of the disk image, which might have occurred in transfer between platforms using a different endianness . BPB values and FAT12, FAT16 and FAT32 file systems are meant to use little-endian representation only and there are no known implementations of variants using big-endian values instead. If

1640-578: A seemingly read-only disk access (such as a DIR A: ) if the medium is not write-protected. Given the dependency on certain values explained above, this may, depending on the actual BPB format and contents, cause MS-DOS/PC DOS and OS/2 to no longer recognize a medium and throw error messages despite the fact that the medium is not defective and can still be read without problems under other operating systems. Windows 9x reads that self-marked disks without any problems but giving some strange values for non-meaning parameters which not exist or are not used when

1722-488: A single-sector setup (logical sector 0 only) for the bootstrap loader, Microsoft's boot sector code has grown to span over logical sectors 0 and 2 since the introduction of FAT32, with logical sector 0 depending on sub-routines in logical sector 2. The Backup Boot Sector area consists of three logical sectors 6, 7, and 8 as well. In some cases, Microsoft also uses sector 12 of the reserved sectors area for an extended boot loader. FAT uses little-endian format for all entries in

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1804-476: A standard 1.44 MB floppy disk to 1.86 MB. SuperStor disk compression technology was replaced with Stac Electronics ' STACKER . An algebraic command line calculator and a utility program to load device drivers from the command line were added. PC DOS 7 also included many optimizations to increase performance and reduce memory usage. The most recent retail release was PC DOS 2000 – released from Austin in 1998 – which found its niche in

1886-431: A stream of bytes . Typically, to read file data, a program provides a memory buffer and the file system retrieves data from the medium and then writes the data to the buffer. A write involves the program providing a buffer of bytes that the file system reads and then stores to the medium. Some file systems, or layers on top of a file system, allow a program to define a record so that a program can read and write data as

1968-585: A structure; not an unorganized sequence of bytes. If a fixed length record definition is used, then locating the n record can be calculated mathematically, which is relatively fast compared to parsing the data for record separators. An identification for each record, also known as a key, allows a program to read, write and update records without regard to their location in storage. Such storage requires managing blocks of media, usually separating key blocks and data blocks. Efficient algorithms can be developed with pyramid structures for locating records. Typically,

2050-428: A terrible problem being sued by people claiming we had stolen their stuff. It could be horribly expensive for us to have our programmers look at code that belonged to someone else because they would then come back and say we stole it and made all this money. We had lost a series of suits on this, and so we didn't want to have a product which was clearly someone else's product worked on by IBM people. We went to Microsoft on

2132-500: A test for a valid media descriptor value at offset 0x015 ) serves as indicator to DOS 3.3 and higher that some kind of BPB is present (although the exact size should not be determined from the jump target since some boot sectors contain private boot loader data following the BPB), while for DOS 1.x (and some DOS 3.0) volumes, they will have to fall back to the DOS 1.x method to detect the format via

2214-432: A user's use of storage space. A file system typically ensures that stored data remains consistent in both normal operations as well as exceptional situations like: Recovery from exceptional situations may include updating metadata, directory entries and handling data that was buffered but not written to storage media. A file system might record events to allow analysis of issues such as: Many file systems access data as

2296-460: A value of 4 here. Volumes declaring 2 FATs in this entry will never be treated as TFAT volumes. If the value differs from 2, some Microsoft operating systems may attempt to mount the volume as a TFAT volume and use the second cluster ( cluster 1 ) of the first FAT to determine the TFAT status. A value of 0 without a FAT32 EBPB (no signature 0x29 or 0x28 at offset 0x042 ) may also indicate

2378-568: A variable-sized root directory in some non-standard FAT12 and FAT16 implementations, which store the root directory start cluster in the cluster 1 entry in the FAT. This extension, however, is not supported by mainstream operating systems, as it can conflict with other uses of the cluster 1 entry for maintenance flags, the current end-of-chain-marker, or TFAT extensions. This value must be adjusted so that directory entries always consume full logical sectors, given that each directory entry takes up 32 bytes. MS-DOS/PC DOS require this value to be

2460-405: Is 256 bytes. For 64 KB clusters, the average unused space is 32 KB. Generally, the allocation unit size is set when the storage is configured. Choosing a relatively small size compared to the files stored, results in excessive access overhead. Choosing a relatively large size results in excessive unused space. Choosing an allocation size based on the average size of files expected to be in

2542-587: Is 512 bytes, which can be reduced downto 128 bytes without support for the FS Information Sector . Floppy drives and controllers use physical sector sizes of 128, 256, 512 and 1024 bytes (e.g., PC/AX). The Atari Portfolio supports a sector size of 512 for volumes larger than 64 KB, 256 bytes for volumes larger 32 KB and 128 bytes for smaller volumes. Magneto-optical drives used sector sizes of 512, 1024 and 2048 bytes. In 2005 some Seagate custom hard disks used sector sizes of 1024 bytes instead of

Design of the FAT file system - Misplaced Pages Continue

2624-513: Is accessible through an operating system structure called the Drive Parameter Block ( DPB ) in DOS and OS/2. The total count of reserved sectors is indicated by a field inside the Boot Sector, and is usually 32 on FAT32 file systems. For FAT32 file systems, the reserved sectors include a File System Information Sector at logical sector 1 and a Backup Boot Sector at logical sector 6. While many other vendors have continued to utilize

2706-534: Is invisible to the end user and the system still works correctly. However this can degrade performance on some storage hardware that work better with contiguous blocks such as hard disk drives . Other hardware such as solid-state drives are not affected by fragmentation. A file system often supports access control of data that it manages. The intent of access control is often to prevent certain users from reading or modifying certain files. Access control can also restrict access by program in order to ensure that data

2788-510: Is modified in a controlled way. Examples include passwords stored in the metadata of the file or elsewhere and file permissions in the form of permission bits, access control lists , or capabilities . The need for file system utilities to be able to access the data at the media level to reorganize the structures and provide efficient backup usually means that these are only effective for polite users but are not effective against intruders. Methods for encrypting file data are sometimes included in

2870-550: Is stored inside the allocation group itself. Additional attributes can be associated on file systems, such as NTFS , XFS , ext2 , ext3 , some versions of UFS , and HFS+ , using extended file attributes . Some file systems provide for user defined attributes such as the author of the document, the character encoding of a document or the size of an image. Some file systems allow for different data collections to be associated with one file name. These separate collections may be referred to as streams or forks . Apple has long used

2952-425: Is the first sector (logical sector 0 with physical CHS address 0/0/1 or LBA address 0). For partitioned storage devices such as hard disks, the Boot Sector is the first sector of a partition, as specified in the partition table of the device. Since DOS 2.0, valid x86-bootable disks must start with either a short jump followed by a NOP ( opstring sequence 0xEB 0x?? 0x90 as seen since DOS 3.0—and on DOS 1.1) or

3034-550: The IBM PC Convertible , IBM's first computer to use 3 + 1 ⁄ 2 -inch floppy disks, released April 1986, and later the IBM Personal System/2 in 1987. In June 1985, IBM and Microsoft signed a long-term Joint Development Agreement to share specified DOS code and create a new operating system from scratch, known at the time as Advanced DOS. On 2 April 1987 OS/2 was announced as the first product produced under

3116-498: The Intel 80286 -derived IBM PC/AT , its next-generation machine. Along with this was DOS 3.00. Despite jumping a whole version number, it again proved little more than an incremental upgrade, adding nothing more substantial than support for the AT's new 1.2 megabyte (MB) floppy disks. Planned networking capabilities in DOS 3.00 were judged too buggy to be usable and Microsoft disabled them prior to

3198-656: The NTFS file system in the Windows NT family of operating systems, and the ODS-2 (On-Disk Structure-2) and higher levels of the Files-11 file system in OpenVMS . In addition to data, the file content, a file system also manages associated metadata which may include but is not limited to: A file system stores associated metadata separate from the content of the file. Most file systems store

3280-411: The embedded software market and elsewhere. PC DOS 2000 is a slipstream of 7.0 with Y2K and other fixes applied. To applications, PC DOS 2000 reports itself as "IBM PC DOS 7.00, revision 1", in contrast to the original PC DOS 7, which reported itself as "IBM PC DOS 7.00, revision 0". PC-DOS 2000 was the last version of IBM PC-DOS that was sold at retail. IBM advertised it as

3362-435: The $ 40 PC DOS compared to 3.4% with the $ 240 CP/M-86. Over the history of IBM PC DOS, various versions were developed by IBM and Microsoft. By the time PC DOS 3.0 was completed, IBM had a team of developers covering the full OS. At that point in time, either IBM or Microsoft completely developed versions of IBM PC DOS going forward. By 1985, the joint development agreement (JDA) between IBM and Microsoft for

Design of the FAT file system - Misplaced Pages Continue

3444-516: The DL value provided at boot time or the value stored in the partition table. This enables booting off alternative drives, even when the VBR code ignores the DL value. This signature must be located at fixed sector offset 0x1FE for sector sizes 512 or higher. If the physical sector size is larger, it may be repeated at the end of the physical sector. Atari STs will assume a disk to be Atari 68000 bootable if

3526-423: The DOS 2.0 format, but could use the DOS 3.0 format as well. A zero entry indicates that this entry is reserved, but not used. A bug in all versions of MS-DOS/PC DOS up to including 7.10 causes these operating systems to crash for CHS geometries with 256 heads, therefore almost all BIOSes choose a maximum of 255 heads only. A zero entry indicates that this entry is reserved, but not used. It must not be used if

3608-471: The IBM PC BIOS supported. BASIC and most of the utilities provided with DOS were substantially upgraded as well. A major undertaking that took almost 10 months of work, DOS 2.0 was more than twice as big as DOS 1.x, occupying around 28 KB of RAM compared to the 12 KB of its predecessor. It would form the basis for all Microsoft consumer-oriented OSes until 2001, when Windows XP (based on Windows NT )

3690-568: The IBM PC. The initial version of DOS was largely based on CP/M-80 1.x and most of its architecture, function calls and file-naming conventions were copied directly from the older OS. The most significant difference was the fact that it introduced a different file system, FAT12 . Unlike all later DOS versions, the DATE and TIME commands were separate executables rather than part of COMMAND.COM . Single-sided 160 kilobyte (KB) 5.25-inch floppies were

3772-650: The IBM ServerGuide Scripting Toolkit. A build of this version of DOS appeared in Norton Ghost from Symantec . Version 7.1 indicates support for FAT32 also in MS-DOS . Most builds of this version of DOS are limited to the kernel files IBMBIO.COM , IBMDOS.COM , and COMMAND.COM . The updated programs FDISK32 and FORMAT32 allow one to prepare FAT32 disks. Additional utilities are taken from PC DOS 2000, where needed. In 1986, IBM announced PC DOS support for client access to

3854-534: The OS's release. In any case, IBM's original plans for the AT had been to equip it with a proper next-generation OS that would use its extended features, but this never materialized. PC DOS 3.1 (released March 1985) fixed the bugs in DOS 3.00 and supported IBM's Network Adapter card on the IBM PC Network . PC DOS 3.2 added support for 3 + 1 ⁄ 2 -inch double-density 720 KB floppy disk drives, supporting

3936-467: The agreement. At the same time, IBM released its next generation of personal computers, the IBM Personal System/2 (PS/2). PC DOS 3.3, released with the PS/2 line, added support for high density 3 + 1 ⁄ 2 -inch 1.44 MB floppy disk drives, which IBM introduced in its 80286-based and higher PS/2 models. The upgrade from DOS 3.2 to 3.3 was completely written by IBM, with no development effort on

4018-811: The boot code area or the serial number in order to ensure that the checksum 0x1234 is not matched (unless the shared fat code overlay would be both IBM PC and Atari ST executable at the same time). The minimum allowed value for non-bootable FAT12/FAT16 volumes with up to 65,535 logical sectors is 32 bytes, or 64 bytes for more than 65,535 logical sectors. The minimum practical value is 128. Some pre-DOS 3.31 OEM versions of DOS used logical sector sizes up to 8192 bytes for logical sectored FATs . Atari ST GEMDOS supports logical sector sizes between 512 and 4096. DR-DOS supports booting off FAT12/FAT16 volumes with logical sector sizes up to 32 KB and INT 13h implementations supporting physical sectors up to 1024 bytes/sector. The minimum logical sector size for standard FAT32 volumes

4100-498: The boot sector parameters altogether and use the media descriptor value from the first byte of the FAT to choose among internally pre-defined parameter templates. Must be greater or equal to 0xF0 since DOS 4.0. On removable drives, DR-DOS will assume the presence of a BPB if this value is greater or equal to 0xF0 , whereas for fixed disks, it must be 0xF8 to assume the presence of a BPB. Initially, these values were meant to be used as bit flags; for any removable media without

4182-401: The checksum over the 256 big-endian words of the boot sector equals 0x1234 . If the boot loader code is IBM compatible, it is important to ensure that the checksum over the boot sector does not match this checksum by accident. If this would happen to be the case, changing an unused bit (e.g., before or after the boot code area) can be used to ensure this condition is not met. In rare cases,

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4264-405: The cluster size can reach 256 KB. Some versions of DR-DOS provide limited support for 128 KB clusters with 512 bytes/sector using a sectors/cluster value of 0. MS-DOS/PC DOS will hang on startup if this value is erroneously specified as 0. Since DR-DOS 7.0x FAT32 formatted volumes use a single-sector boot sector, FS info sector and backup sector, some volumes formatted under DR-DOS use

4346-421: The computer main memory can be set up as a RAM disk that serves as a storage device for a file system. File systems such as tmpfs can store files in virtual memory . A virtual file system provides access to files that are either computed on request, called virtual files (see procfs and sysfs ), or are mapping into another, backing storage. From c.  1900 and before the advent of computers

4428-519: The concepts. The logical file system layer provides relatively high-level access via an application programming interface (API) for file operations including open, close, read and write – delegating operations to lower layers. This layer manages open file table entries and per-process file descriptors. It provides file access, directory operations, security and protection. The virtual file system , an optional layer, supports multiple concurrent instances of physical file systems, each of which called

4510-663: The default 512 bytes. Advanced Format hard disks use 4096 bytes per sector ( 4Kn ) since 2010, but will also be able to emulate 512 byte sectors ( 512e ) for a transitional period. Linux, and by extension Android, supports a logical sector size far larger, officially documented in the Man page for the filesystem utilities as up to 32KB. For most DOS-based operating systems, the maximum cluster size remains at 32 KB (or 64 KB) even for sector sizes larger than 512 bytes. For logical sector sizes of 1 KB, 2 KB and 4 KB, Windows NT 4.0 supports cluster sizes of 128 KB, while for 2 KB and 4 KB sectors

4592-678: The development of PC DOS had each company giving the other company a completely developed version. Most of the time branded versions were identical, but there were some cases in which each of the companies made minor modifications to their version of DOS. In the fall of 1984, IBM gave all the source code and documentation of the internally developed IBM TopView for DOS to Microsoft so that Microsoft could more fully understand how to develop an object-oriented operating environment , overlapping windows (for its development of Windows 2.0 ) and multitasking . Microsoft first licensed, then purchased 86-DOS from Seattle Computer Products (SCP), which

4674-491: The disk was formatted with older BPB specification, e.g. disk serial number (which exists only for disks formatted on DOS 5.0 or later, and in Windows 9x after overwriting OEM label with ?????IHC will report it as 0000-0000 or any other value stored in disk serial number field when using disk formatted on other system). This applies only to removable disk drives. Some boot loaders make adjustments or refuse to pass control to

4756-416: The file system. This is very effective since there is no need for file system utilities to know the encryption seed to effectively manage the data. The risks of relying on encryption include the fact that an attacker can copy the data and use brute force to decrypt the data. Additionally, losing the seed means losing the data. Some operating systems allow a system administrator to enable disk quotas to limit

4838-526: The header (except for, where explicitly mentioned, some entries on Atari ST boot sectors) and the FAT(s). It is possible to allocate more FAT sectors than necessary for the number of clusters. The end of the last sector of each FAT copy can be unused if there are no corresponding clusters. The total number of sectors (as noted in the boot record) can be larger than the number of sectors used by data (clusters × sectors per cluster), FATs (number of FATs × sectors per FAT),

4920-495: The length of a file name. Some file systems match file names as case sensitive and others as case insensitive. For example, the names MYFILE and myfile match the same file for case insensitive, but different files for case sensitive. Most modern file systems allow a file name to contain a wide range of characters from the Unicode character set. Some restrict characters such as those used to indicate special attributes such as

5002-409: The logical sector size is larger than 512 bytes, the remainder is not included in the checksum and is typically zero-filled. Since some PC operating systems erroneously do not accept FAT formatted floppies if the 0x55 0xAA signature is not present here, it is advisable to place the 0x55 0xAA in this place (and add an IBM compatible boot loader or stub) and use an unused word in the private data or

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5084-557: The logical sectors entry at offset 0x013 is zero. DOS 3.2 BPB: Officially, MS-DOS 3.20 still used the DOS 3.0 format, but SYS and FORMAT were adapted to support a 6 bytes longer format already (of which not all entries were used). It must not be used if the logical sectors entry at offset 0x013 is zero. DOS 3.31 BPB: Officially introduced with DOS 3.31 and not used by DOS 3.2, some DOS 3.2 utilities were designed to be aware of this new format already. Official documentation recommends to trust these values only if

5166-508: The logical sectors entry at offset 0x013 is zero. A zero entry indicates that this entry is reserved, but not used. A value of 0 may indicate LBA-only access, but may cause a divide-by-zero exception in some boot loaders, which can be avoided by storing a neutral value of 1 here, if no CHS geometry can be reasonably emulated. A bug in all versions of MS-DOS/PC DOS up to including 7.10 causes these operating systems to crash for CHS geometries with 256 heads, therefore almost all BIOSes choose

5248-571: The machine, including the operating system, would come from outside vendors. This radical break from company tradition of in-house development was one of the key decisions that made the IBM PC an industry standard. Microsoft , founded five years earlier by Bill Gates , was eventually selected for the operating system. IBM wanted Microsoft to retain ownership of whatever software it developed, and wanted nothing to do with helping Microsoft, other than making suggestions from afar. According to task force member Jack Sams : The reasons were internal. We had

5330-401: The media byte in the FAT (in logical sector 1 ). Although officially documented as free for OEM use, MS-DOS/PC DOS (since 3.1), Windows 95/98/SE/ME and OS/2 check this field to determine which other parts of the boot record can be relied upon and how to interpret them. Therefore, setting the OEM label to arbitrary or bogus values may cause MS-DOS, PC DOS and OS/2 to not recognize

5412-595: The names of all the files in one directory in one place—the directory table for that directory—which is often stored like any other file. Many file systems put only some of the metadata for a file in the directory table, and the rest of the metadata for that file in a completely separate structure, such as the inode . Most file systems also store metadata not associated with any one particular file. Such metadata includes information about unused regions— free space bitmap , block availability map —and information about bad sectors . Often such information about an allocation group

5494-659: The new features from MS-DOS 6.0 appeared in PC ;DOS 6.1 including the new boot menu support and the new commands CHOICE , DELTREE , and MOVE . QBasic was dropped and the MS-DOS Editor was replaced with the IBM E Editor . It also licensed components of Central Point's PC Tools , such as Central Point Backup Utility (CPBACKUP). PC DOS 6.1 reports itself as DOS 6.00. PC DOS 6.3 followed in December. PC DOS 6.3

5576-556: The number of people he had to deal with at the ESD (Entry Systems Division) facility in Boca Raton, Florida . Perhaps the first public mention of the operating system was in July 1981, when Byte discussed rumors of a forthcoming personal computer with "a CP/M-like DOS ... to be called, simply, 'IBM Personal Computer DOS ' ". 86-DOS was rebranded IBM PC DOS 1.0 for its August 1981 release with

5658-526: The only disk format supported. In late 1981, Paterson, now at Microsoft, began writing PC DOS 1.10. It debuted in May 1982 along with the Revision ;B IBM PC. Support for the new double-sided drives was added, allowing 320 KB per disk. A number of bugs were fixed, and error messages and prompts were made less cryptic. The DEBUG.EXE was now able to load files greater than 64 KB in size. Later,

5740-540: The part of Microsoft, who were working on "Advanced DOS 1.0". DOS 3.30 was the last version designed with the IBM XT and floppy-only systems in mind; it became one of the most popular versions and many users preferred it to its buggy successor. PC DOS 4.0 (internally known as DOS 3.4 originally) shipped July 1988. DOS 4.0 had some compatibility issues with low-level disk utilities due to some internal data structure changes. DOS 4.0 used more memory than DOS 3.30 and it also had

5822-528: The proposition that we wanted this to be their product. IBM first contacted Microsoft to look the company over in July 1980. Negotiations continued over the months that followed, and the paperwork was officially signed in early November. Although IBM expected that most customers would use PC DOS, the IBM PC also supported CP/M-86 , which became available six months after PC DOS, and UCSD p-System operating systems. IBM's expectation proved correct: one survey found that 96.3% of PCs were ordered with

5904-471: The root directory (n/a for FAT32), and hidden sectors including the boot sector: this would result in unused sectors at the end of the volume. If a partition contains more sectors than the total number of sectors occupied by the file system it would also result in unused sectors, at the end of the partition, after the volume. On non-partitioned storage devices , such as floppy disks , the Boot Sector ( VBR )

5986-537: The signature at sector offset 0x042 is 0x29 and both total sector entries are 0, the file system entry may serve as a 64-bit total sector count entry and the OEM label entry may be used as alternative file system type instead of the normal entry at offset 0x052 . In a similar fashion, if this entry is set to " EXFAT␠␠␠ ", it indicates the usage of an exFAT BPB located at sector offset 0x040 to 0x077 , whereas NTFS volumes use " NTFS␠␠␠␠ " to indicate an NTFS BPB . (In conjunction with at least

6068-429: The storage tends to minimize unusable space. As a file system creates, modifies and deletes files, the underlying storage representation may become fragmented . Files and the unused space between files will occupy allocation blocks that are not contiguous. A file becomes fragmented if space needed to store its content cannot be allocated in contiguous blocks. Free space becomes fragmented when files are deleted. This

6150-442: The terms file system , filing system and system for filing were used to describe methods of organizing, storing and retrieving paper documents. By 1961, the term file system was being applied to computerized filing alongside the original meaning. By 1964, it was in general use. A local file system's architecture can be described as layers of abstraction even though a particular file system design may not actually separate

6232-509: The use of the High Memory Area (HMA) and Upper Memory Blocks (UMBs) on 80286 and later systems to reduce its conventional memory usage. Also all DOS commands now supported the /? option to display command syntax. Aside from IBM's PC DOS, MS-DOS was the only other version available as OEM editions vanished since by this time PCs were 100% compatible so customizations for hardware differences were no longer necessary. The POWER.EXE

6314-464: The volume properly and cause data corruption on writes. Common examples are " IBM␠␠3.3 ", " MSDOS5.0 ", " MSWIN4.1 ", " IBM␠␠7.1 ", " mkdosfs␠ ", and " FreeDOS␠ ". Some vendors store licensing info or access keys in this entry. The Volume Tracker in Windows 95/98/SE/ME will overwrite the OEM label with " ?????IHC " signatures (a left-over from " ␠OGACIHC " for " Chicago ") even on

6396-436: Was also sold by that company as MS-DOS . Both operating systems were identical or almost identical until 1993, when IBM began selling PC DOS 6.1 with new features. The collective shorthand for PC DOS and MS-DOS was DOS , which is also the generic term for disk operating system, and is shared with dozens of disk operating systems called DOS . The IBM task force assembled to develop the IBM PC decided that critical components of

6478-552: Was also used in OS/2 for the PowerPC . PC DOS 6.3 also featured SuperStor disk compression technology from Addstor . PC DOS 7 was released in April 1995 and was the last release of DOS before IBM software development (other than the development IBM ViaVoice ) moved to Austin. The REXX programming language was added, as well as support for a new floppy disk format, XDF , which extended

6560-488: Was introduced that has the APM standard in version 5.02. This was the last version of DOS that IBM and Microsoft shared the full code for, and the DOS that was integrated into OS/2 2.0's, and later Windows NT's, virtual DOS machine . PC DOS remained a rebranded version of MS-DOS until 1993. IBM and Microsoft parted ways—MS-DOS 6 was released in March, and PC DOS 6.1 (separately developed) followed in June. Most of

6642-558: Was modified for the IBM PC by Microsoft employee Bob O'Rear with assistance from SCP (later Microsoft) employee Tim Paterson . O'Rear got 86-DOS to run on the prototype PC in February 1981. 86-DOS had to be converted from 8-inch to 5.25-inch floppy disks and integrated with the BIOS , which Microsoft was helping IBM to write. IBM had more people writing requirements for the computer than Microsoft had writing code. O'Rear often felt overwhelmed by

6724-560: Was released. In October 1983 (officially 1 November 1983) DOS 2.1 debuted. It fixed some bugs and added support for half-height floppy drives and the new IBM PCjr . In 1983, Compaq released the Compaq Portable , the first 100% IBM PC compatible and licensed their own OEM version of DOS 1.10 (quickly replaced by DOS 2.00) from Microsoft. Other PC compatibles followed suit, most of which included hardware-specific DOS features, although some were generic. In August 1984, IBM introduced

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