In computing, a file system (often also written as filesystem) is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. Computing is usually defined like the activity of using and developing Computer technology Computer hardware and software. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually File systems may use a data storage device such as a hard disk or CD-ROM and involve maintaining the physical location of the files, they might provide access to data on a file server by acting as clients for a network protocol (e. A data storage device is a device for recording (storing information (data A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable g. , NFS, SMB, or 9P clients), or they may be virtual and exist only as an access method for virtual data (e. Network File System (NFS is a Network file system protocol originally developed by Sun Microsystems in 1983 allowing a user on a client Computer to access In Computer networking, Server Message Block ( SMB) operates as an application-level network protocol mainly used to provide Shared access 9P (or the Plan 9 Filesystem Protocol or Styx) is a Network protocol developed for the Plan 9 from Bell Labs Distributed operating system g. , procfs). On many Unix -like computer systems procfs, short for process File system, consists of a pseudo file system (a file system dynamically generated

More formally, a file system is a set of abstract data types that are implemented for the storage, hierarchical organization, manipulation, navigation, access, and retrieval of data. In Computing, an abstract data type ( ADT) is a specification of a set of data and the set of operations that can be performed on the data Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's File systems share much in common with database technology, but it is debatable whether a file system can be classified as a special-purpose database (DBMS). A database management system ( DBMS) is Computer software designed for the purpose of managing Databases DBMSes may use any of a variety of Data models

Data retrieval process

When a computer retrieves any file from a disk, the program in which the file is opened first calls on an API (Application Programming Interface) in order to build a dialogue box for viewing the file or folder. The operating system calls on the IFS (installable file system) manager. The IFS calls on the correct FSD (file system driver) in order to open the selected file from a choice of FSD's that work with different storage systems.

The FSD gets the location on the disk for the first cluster of the file from the FAT (File Allocation Table) or, in the case of NTFS, the MFT (Master File Table). In short, the whole point of these are to map out all the files on the disk and record where they are located (which track and sector of the disk).

Once the FSD knows where the file is located, it passes the read command to the I/O subsystem (input/output subsystem). This is generally an assistant to FSDs, doing chores such as routing messages back and forth between FSDs and lower, device-specific drivers. The VTD (Volume Tracking driver) might come into action if the file is not located on a drive. The VTD would only come into action if the file was stored on a floppy, CD, DVD, or other removable drive. The only thing the VTD does is determine if the correct disk is in the correct drive. Once this is done, the operation is passed off to the TSD (Type Specific Driver) which passes the read signal to the correct drive adapter. There is a separate TSD for hard drives, floppy drives, etc. Finally, the adapter takes over, moving the read/write head to the correct series of disk clusters to read the file into RAM so that it can be viewed and edited.

Aspects of file systems

The most familiar file systems make use of an underlying data storage device that offers access to an array of fixed-size blocks, sometimes called sectors, generally a power of 2 in size (512 bytes or 1, 2, or 4 kib are most common). A data storage device is a device for recording (storing information (data In Computing (specifically data transmission and data storage) block is a sequence of Bytes or Bits having a nominal length (a block size In Mathematics, a power of two is any of the Integer powers of the number two; in other words two multiplied by itself a certain A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International The file system software is responsible for organizing these sectors into files and directories, and keeping track of which sectors belong to which file and which are not being used. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories Most file systems address data in fixed-sized units called "clusters" or "blocks" which contain a certain number of disk sectors (usually 1-64). In computer File systems a cluster is the unit of disk space allocation for files and directories In Computing (specifically data transmission and data storage) block is a sequence of Bytes or Bits having a nominal length (a block size In the context of Computer Disk storage, a sector is a subdivision of a track (Figure 1 item A on a Magnetic disk or Optical disc This is the smallest logical amount of disk space that can be allocated to hold a file.

However, file systems need not make use of a storage device at all. A file system can be used to organize and represent access to any data, whether it be stored or dynamically generated (e. g. , procfs). On many Unix -like computer systems procfs, short for process File system, consists of a pseudo file system (a file system dynamically generated

File names

Whether the file system has an underlying storage device or not, file systems typically have directories which associate file names with files, usually by connecting the file name to an index into a file allocation table of some sort, such as the FAT in a DOS file system, or an inode in a Unix-like file system. A filename is a special kind of string used to uniquely identify a file stored on the File system of a computer Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market In Computing, an inode is a Data structure on a traditional Unix -style File system such as UFS. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming Directory structures may be flat, or allow hierarchies where directories may contain subdirectories. In some file systems, file names are structured, with special syntax for filename extensions and version numbers. A filename extension is a suffix to the name of a Computer file applied to indicate the encoding convention ( File format) of its contents In others, file names are simple strings, and per-file metadata is stored elsewhere. Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media

Meta data

Other bookkeeping information is typically associated with each file within a file system. The length of the data contained in a file may be stored as the number of blocks allocated for the file or as an exact byte count. File size Measures the Size of a Computer file. Typically it is measured in Bytes with a Prefix. A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. The time that the file was last modified may be stored as the file's timestamp. In Computer science and Computer programming, system time represents a computer system's notion of the passing of Time. Some file systems also store the file creation time, the time it was last accessed, and the time that the file's meta-data was changed. (Note that many early PC operating systems did not keep track of file times. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated ) Other information can include the file's device type (e. g. , block, character, socket, subdirectory, etc. An Internet socket (or commonly a network socket or socket) is an end-point of a bidirectional process-to-process communication flow across an IP In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories ), its owner user-ID and group-ID, and its access permission settings (e. Users in a Computing context refers to one who uses a computer system In computing the term group generally refers to a grouping of users. Most modern File systems have methods of administering permissions or access rights to specific users and groups of users g. , whether the file is read-only, executable, etc. In Computing, an executable (file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains ).

Arbitrary attributes can be associated on advanced file systems, such as XFS, ext2/ext3, some versions of UFS, and HFS+, using extended file attributes. XFS is a high-performance Journaling file system created by Silicon Graphics, originally for their IRIX Operating system and later ported to The ext2 or second extended file system is a File system for the Linux kernel. The ext3 or third extended filesystem is a journaled file system that is commonly used by the Linux Operating system. The Unix file system ( UFS) is a File system used by many Unix and Unix-like operating systems Extended file attributes is a File system feature that enables users to associate Computer files with Metadata not interpreted by the filesystem whereas This feature is implemented in the kernels of Linux, FreeBSD and Mac OS X operating systems, and allows metadata to be associated with the file at the file system level. Linux is an operating system kernel used by a family of Unix-like Operating systems These are popularly termed Linux operating systems and FreeBSD is a Unix-like free Operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD branch through Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently This, for example, could be the author of a document, the character encoding of a plain-text document, or a checksum.

Hierarchical file systems

The hierarchical file system was an early research interest of Dennis Ritchie of Unix fame; previous implementations were restricted to only a few levels, notably the IBM implementations, even of their early databases like IMS. Dennis MacAlistair Ritchie (born September 9, 1941) is an American computer scientist notable for his influence on C and other Programming After the success of Unix, Ritchie extended the file system concept to every object in his later operating system developments, such as Plan 9 and Inferno. Plan 9 from Bell Labs is a Distributed operating system, primarily used for research Inferno is an Operating system for creating and supporting distributed services

Facilities

Traditional file systems offer facilities to create, move and delete both files and directories. They lack facilities to create additional links to a directory (hard links in Unix), rename parent links (". In Computing, a hard link is a directory reference or pointer to a file on a storage volume Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer . " in Unix-like OS), and create bidirectional links to files. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming

Traditional file systems also offer facilities to truncate, append to, create, move, delete and in-place modify files. They do not offer facilities to prepend to or truncate from the beginning of a file, let alone arbitrary insertion into or deletion from a file. The operations provided are highly asymmetric and lack the generality to be useful in unexpected contexts. For example, interprocess pipes in Unix have to be implemented outside of the file system because the pipes concept does not offer truncation from the beginning of files. In Unix-like computer Operating systems a pipeline is the original software pipeline: a set of processes chained by their Standard Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer In Mathematics, truncation is the term for limiting the number of digits right of the Decimal point, by discarding the least significant ones

Secure access

Secure access to basic file system operations can be based on a scheme of access control lists or capabilities. In Computer security, an access control list ( ACL) is a list of permissions attached to an object Capability-based security is a concept in the design of Secure computing systems Research has shown access control lists to be difficult to secure properly, which is why research operating systems tend to use capabilities. Commercial file systems still use access control lists. see: secure computing

Types of file systems

File system types can be classified into disk file systems, network file systems and special purpose file systems. This article describes how security can be achieved through design and engineering

Disk file systems

A disk file system is a file system designed for the storage of files on a data storage device, most commonly a disk drive, which might be directly or indirectly connected to the computer. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually A data storage device is a device for recording (storing information (data Disk storage is a general category of a Computer storage mechanisms in which data is recorded on planar round and rotating surfaces ( disks, discs, or Examples of disk file systems include FAT (FAT12, FAT16, FAT32), NTFS, HFS and HFS+, ext2, ext3, ISO 9660, ODS-5, and UDF. Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Hierarchical File System ( HFS) is a File system developed by Apple Inc HFS Plus or HFS+ is a File system developed by Apple Inc to replace their Hierarchical File System (HFS as the primary file system used The ext2 or second extended file system is a File system for the Linux kernel. The ext3 or third extended filesystem is a journaled file system that is commonly used by the Linux Operating system. ISO 9660 a standard published by the International Organization for Standardization (ISO defines a File system for CD-ROM media Files-11, also known as on-disk structure, is the File system used by Hewlett-Packard 's OpenVMS Operating system, and also (in a simpler The Universal Disk Format ( UDF) is a format specification of a File system for storing files on optical media Some disk file systems are journaling file systems or versioning file systems. A journaling file system is a File system that logs changes to a journal (usually a circular log in a dedicated area before committing them to the main file A versioning file system is any computer File system which allows a Computer file to exist in several versions at the same time

Flash file systems

A flash file system is a file system designed for storing files on flash memory devices. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed These are becoming more prevalent as the number of mobile devices is increasing, and the capacity of flash memories catches up with hard drives.

While a block device layer can emulate a disk drive so that a disk file system can be used on a flash device, this is suboptimal for several reasons:

• Erasing blocks: Flash memory blocks have to be explicitly erased before they can be written to. The time taken to erase blocks can be significant, thus it is beneficial to erase unused blocks while the device is idle.
• Random access: Disk file systems are optimized to avoid disk seeks whenever possible, due to the high cost of seeking. In Computer science, random access (sometimes called direct access) is the ability to access an arbitrary element of a sequence in equal time Seek time is one of the three delays associated with reading or writing Data on a Computer 's Disk drive, and somewhat similar for CD or Flash memory devices impose no seek latency.
• Wear levelling: Flash memory devices tend to wear out when a single block is repeatedly overwritten; flash file systems are designed to spread out writes evenly. Wear levelling (also written wear leveling) is a technique for prolonging the Service life of some kinds of erasable Computer storage media such as

Log-structured file systems have all the desirable properties for a flash file system. A log-structured filesystem is a File system design first proposed by John K Such file systems include JFFS2 and YAFFS. Journalling Flash File System version 2 or JFFS2 is a Log-structured file system for use in Flash memory devices YAFFS ( Yet Another Flash File System) was designed and written by Charles Manning, of Whitecliffs, New Zealand for the company Aleph One

Database file systems

A new concept for file management is the concept of a database-based file system. Instead of, or in addition to, hierarchical structured management, files are identified by their characteristics, like type of file, topic, author, or similar metadata. Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media

Transactional file systems

Each disk operation may involve changes to a number of different files and disk structures. In many cases, these changes are related, meaning that it is important that they all be executed at the same time. Take for example a bank sending another bank some money electronically. The bank's computer will "send" the transfer instruction to the other bank and also update its own records to indicate the transfer has occurred. If for some reason the computer crashes before it has had a chance to update its own records, then on reset, there will be no record of the transfer but the bank will be missing some money.

Transaction processing introduces the guarantee that at any point while it is running, a transaction can either be finished completely or reverted completely (though not necessarily both at any given point). For other meanings see the disambiguation page at Transaction. This means that if there is a crash or power failure, after recovery, the stored state will be consistent. (Either the money will be transferred or it will not be transferred, but it won't ever go missing "in transit". )

This type of file system is designed to be fault tolerant, but may incur additional overhead to do so.

Journaling file systems are one technique used to introduce transaction-level consistency to filesystem structures. A journaling file system is a File system that logs changes to a journal (usually a circular log in a dedicated area before committing them to the main file

Network file systems

Main article: Network file system

A network file system is a file system that acts as a client for a remote file access protocol, providing access to files on a server. A network file system is any computer File system that supports sharing of files, printers and other resources as Persistent storage over Examples of network file systems include clients for the NFS, AFS, SMB protocols, and file-system-like clients for FTP and WebDAV. Network File System (NFS is a Network file system protocol originally developed by Sun Microsystems in 1983 allowing a user on a client Computer to access The Andrew File System ( AFS) is a distributed networked file system which uses a set of trusted servers to present a homogeneous location-transparent file name space In Computer networking, Server Message Block ( SMB) operates as an application-level network protocol mainly used to provide Shared access Web-based Distributed Authoring and Versioning, or WebDAV, is a set of extensions to the Hypertext Transfer Protocol (HTTP that allows users to collaboratively edit

Special purpose file systems

Main article: special file system

A special purpose file system is basically any file system that is not a disk file system or network file system. A special file system presents non-file elements of an operating system as files This includes systems where the files are arranged dynamically by software, intended for such purposes as communication between computer processes or temporary file space. A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually In computing a process is an instance of a Computer program that is being sequentially executed by a computer system that has the ability to run several computer

Special purpose file systems are most commonly used by file-centric operating systems such as Unix. Examples include the procfs (/proc) file system used by some Unix variants, which grants access to information about processes and other operating system features. On many Unix -like computer systems procfs, short for process File system, consists of a pseudo file system (a file system dynamically generated In computing a process is an instance of a Computer program that is being sequentially executed by a computer system that has the ability to run several computer

Deep space science exploration craft, like Voyager I & II used digital tape based special file systems. The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Most modern space exploration craft like Cassini-Huygens used Real-time operating system file systems or RTOS influenced file systems. Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its A real-time operating system ( RTOS; generally pronounced as "are-toss" is a multitasking Operating system intended for real-time The Mars Rovers are one such example of an RTOS file system, important in this case because they are implemented in flash memory. Mars rover is a Spacecraft which propels itself across the surface of Mars after landing.

File systems and operating systems

Most operating systems provide a file system, as a file system is an integral part of any modern operating system. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination Early microcomputer operating systems' only real task was file management — a fact reflected in their names (see DOS). microcomputer is a Computer with a Microprocessor as its Central processing unit. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market Some early operating systems had a separate component for handling file systems which was called a disk operating system. On some microcomputers, the disk operating system was loaded separately from the rest of the operating system. On early operating systems, there was usually support for only one, native, unnamed file system; for example, CP/M supports only its own file system, which might be called "CP/M file system" if needed, but which didn't bear any official name at all. CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall

Because of this, there needs to be an interface provided by the operating system software between the user and the file system. This interface can be textual (such as provided by a command line interface, such as the Unix shell, or OpenVMS DCL) or graphical (such as provided by a graphical user interface, such as file browsers). A Unix shell, is a command line shell that provides the traditional User interface for the Unix Operating system and for Unix-like DCL, the DIGITAL Command Language, is the standard command languageadopted by most of the A file manager or file browser is a Computer program that provides a User interface to work with File systems The most common operations used If graphical, the metaphor of the folder, containing documents, other files, and nested folders is often used (see also: directory and folder). In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories

Flat file systems

In a flat file system, there are no subdirectories—everything is stored at the same (root) level on the media, be it a hard disk, floppy disk, etc. In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories In computer File systems the root directory is the first or top-most directory in a hierarchy A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased While simple, this system rapidly becomes inefficient as the number of files grows, and makes it difficult for users to organize data into related groups.

Like many small systems before it, the original Apple Macintosh featured a flat file system, called Macintosh File System. Macintosh, commonly nicknamed Mac is a Brand name which covers several lines of Personal computers designed developed and marketed by Apple Inc Macintosh File System ( MFS) is a volume format (or disk File system) created by Apple Computer for storing files on 400K Floppy disks Its version of Mac OS was unusual in that the file management software (Macintosh Finder) created the illusion of a partially hierarchical filing system on top of MFS. Mac OS is the trademarked name for a series of Graphical user interface -based Operating systems developed by Apple Inc The Finder is the default application program used on the Mac OS and Mac OS X Operating systems that is responsible for the overall user-management This structure meant that every file on a disk had to have a unique name, even if it appeared to be in a separate folder. MFS was quickly replaced with Hierarchical File System, which supported real directories. Hierarchical File System ( HFS) is a File system developed by Apple Inc In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories

File systems under Unix-like operating systems

Unix-like operating systems create a virtual file system, which makes all the files on all the devices appear to exist in a single hierarchy. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming This means, in those systems, there is one root directory, and every file existing on the system is located under it somewhere. In computer File systems the root directory is the first or top-most directory in a hierarchy Furthermore, the root directory does not have to be in any physical place. It might not be on your first hard drive - it might not even be on your computer. Unix-like systems can use a network shared resource as its root directory.

Unix-like systems assign a device name to each device, but this is not how the files on that device are accessed. Instead, to gain access to files on another device, you must first inform the operating system where in the directory tree you would like those files to appear. This process is called mounting a file system. Mounting, in Computer science, is the process of making a File system ready for use by the Operating system, typically by reading certain index data structures For example, to access the files on a CD-ROM, one must tell the operating system "Take the file system from this CD-ROM and make it appear under such-and-such directory". CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable The directory given to the operating system is called the mount point - it might, for example, be /media. Mounting, in Computer science, is the process of making a File system ready for use by the Operating system, typically by reading certain index data structures The /media directory exists on many Unix systems (as specified in the Filesystem Hierarchy Standard) and is intended specifically for use as a mount point for removable media such as CDs, DVDs and like floppy disks. The Filesystem Hierarchy Standard (FHS defines the main directories and their contents in most Linux -based computer Operating systems It is a formalization and extension It may be empty, or it may contain subdirectories for mounting individual devices. Generally, only the administrator (i. A system administrator, systems administrator, or sysadmin, is a person employed to maintain and operate a Computer system and/or network. e. root user) may authorize the mounting of file systems. On many computer Operating systems the superuser, or root, is a special User account used for System administration.

Unix-like operating systems often include software and tools that assist in the mounting process and provide it new functionality. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming Some of these strategies have been coined "auto-mounting" as a reflection of their purpose.

1. In many situations, file systems other than the root need to be available as soon as the operating system has booted. In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system All Unix-like systems therefore provide a facility for mounting file systems at boot time. System administrators define these file systems in the configuration file fstab, which also indicates options and mount points. A system administrator, systems administrator, or sysadmin, is a person employed to maintain and operate a Computer system and/or network. The fstab (for File systems table) file is commonly found on Unix systems as part of the system configuration.
2. In some situations, there is no need to mount certain file systems at boot time, although their use may be desired thereafter. In Computing, booting ( booting up) is a bootstrapping process that starts Operating systems when the user turns on a Computer system There are some utilities for Unix-like systems that allow the mounting of predefined file systems upon demand.
3. Removable media have become very common with microcomputer platforms. microcomputer is a Computer with a Microprocessor as its Central processing unit. They allow programs and data to be transferred between machines without a physical connection. Common examples include USB flash drives, CD-ROMs, and DVDs. CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is Utilities have therefore been developed to detect the presence and availability of a medium and then mount that medium without any user intervention.
4. Progressive Unix-like systems have also introduced a concept called supermounting; see, for example, the Linux supermount-ng project. For example, a floppy disk that has been supermounted can be physically removed from the system. Under normal circumstances, the disk should have been synchronized and then unmounted before its removal. Provided synchronization has occurred, a different disk can be inserted into the drive. The system automatically notices that the disk has changed and updates the mount point contents to reflect the new medium. Similar functionality is found on standard Windows machines.
5. A similar innovation preferred by some users is the use of autofs, a system that, like supermounting, eliminates the need for manual mounting commands. The difference from supermount, other than compatibility in an apparent greater range of applications such as access to file systems on network servers, is that devices are mounted transparently when requests to their file systems are made, as would be appropriate for file systems on network servers, rather than relying on events such as the insertion of media, as would be appropriate for removable media. In computing a distributed file system is a Network file system where a single File system can be distributed across several physical computer nodes

File systems under Linux

Linux supports many different file systems, but common choices for the system disk include the ext* family (such as ext2 and ext3), XFS, and JFS. Linux (commonly pronounced ˈlɪnəks The ext2 or second extended file system is a File system for the Linux kernel. The ext3 or third extended filesystem is a journaled file system that is commonly used by the Linux Operating system. XFS is a high-performance Journaling file system created by Silicon Graphics, originally for their IRIX Operating system and later ported to Journaled File System or JFS is a 64-bit Journaling filesystem created by IBM.

File systems under Mac OS X

Mac OS X uses a file system that it inherited from classic Mac OS called HFS Plus. Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently Mac OS is the trademarked name for a series of Graphical user interface -based Operating systems developed by Apple Inc HFS Plus or HFS+ is a File system developed by Apple Inc to replace their Hierarchical File System (HFS as the primary file system used HFS Plus is a metadata-rich and case preserving file system. Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media When a Computer File system stores text the computer may keep or discard case information Due to the Unix roots of Mac OS X, Unix permissions were added to HFS Plus. Later versions of HFS Plus added journaling to prevent corruption of the file system structure and introduced a number of optimizations to the allocation algorithms in an attempt to defragment files automatically without requiring an external defragmenter. A journaling file system is a File system that logs changes to a journal (usually a circular log in a dedicated area before committing them to the main file

Filenames can be up to 255 characters. HFS Plus uses Unicode to store filenames. In Computing, Unicode is an Industry standard allowing Computers to consistently represent and manipulate text expressed in most of the world's On Mac OS X, the filetype can come from the type code, stored in file's metadata, or the filename. A file format is a particular way to encode information for storage in a Computer file. A type code is the only mechanism used in pre- Mac OS X versions of the Macintosh Operating system to denote a file's format, in a manner similar

HFS Plus has three kinds of links: Unix-style hard links, Unix-style symbolic links and aliases. In Computing, a hard link is a directory reference or pointer to a file on a storage volume In Computing, a symbolic link (also symlink or soft link) is a special type of file that contains a reference to another In Mac OS System 7 and later an alias is a small file that represents another object in a local remote or removable File system. Aliases are designed to maintain a link to their original file even if they are moved or renamed; they are not interpreted by the file system itself, but by the File Manager code in userland.

Mac OS X also supports the UFS file system, derived from the BSD Unix Fast File System via NeXTSTEP. The Unix file system ( UFS) is a File system used by many Unix and Unix-like operating systems Nextstep was the original object-oriented, multitasking Operating system that NeXT Computer developed to run on its range of proprietary computers However, as of Mac OS X 10. 5 (Leopard), Mac OS X can no longer be installed on a UFS volume, nor can a pre-Leopard system installed on a UFS volume be upgraded to Leopard. [1]

File systems under Plan 9 from Bell Labs

Plan 9 from Bell Labs was originally designed to extend some of Unix's good points, and to introduce some new ideas of its own while fixing the shortcomings of Unix. Plan 9 from Bell Labs is a Distributed operating system, primarily used for research

With respect to file systems, the Unix system of treating things as files was continued, but in Plan 9, everything is treated as a file, and accessed as a file would be (i. e. , no ioctl or mmap). In computing an ioctl (aɪˈɒktəl or "i-o-control" is part of the user -to- kernel interface of a conventional operating system In Computing, mmap is a POSIX -compliant Unix System call that maps files or devices into memory Perhaps surprisingly, while the file interface is made universal it is also simplified considerably, for example symlinks, hard links and suid are made obsolete, and an atomic create/open operation is introduced. More importantly the set of file operations becomes well defined and subversions of this like ioctl are eliminated.

Secondly, the underlying 9P protocol was used to remove the difference between local and remote files (except for a possible difference in latency). 9P (or the Plan 9 Filesystem Protocol or Styx) is a Network protocol developed for the Plan 9 from Bell Labs Distributed operating system In Computing and especially Computer networks lag (slang is a symptom where the result of an action appears later than expected This has the advantage that a device or devices, represented by files, on a remote computer could be used as though it were the local computer's own device(s). This means that under Plan 9, multiple file servers provide access to devices, classing them as file systems. Servers for "synthetic" file systems can also run in user space bringing many of the advantages of micro kernel systems while maintaining the simplicity of the system.

Everything on a Plan 9 system has an abstraction as a file; networking, graphics, debugging, authentication, capabilities, encryption, and other services are accessed via I-O operations on file descriptors. For example, this allows the use of the IP stack of a gateway machine without need of NAT, or provides a network-transparent window system without the need of any extra code.

Another example: a Plan-9 application receives FTP service by opening an FTP site. The ftpfs server handles the open by essentially mounting the remote FTP site as part of the local file system. With ftpfs as an intermediary, the application can now use the usual file-system operations to access the FTP site as if it were part of the local file system. A further example is the mail system which uses file servers that synthesize virtual files and directories to represent a user mailbox as /mail/fs/mbox. The wikifs provides a file system interface to a wiki. wikifs is a Wiki File system for the Plan 9 and Inferno Operating systems It allows wiki pages to be served as web pages and viewed

These file systems are organized with the help of private, per-process namespaces, allowing each process to have a different view of the many file systems that provide resources in a distributed system.

The Inferno operating system shares these concepts with Plan 9. Inferno is an Operating system for creating and supporting distributed services

File systems under Microsoft Windows

Windows makes use of the FAT, NTFS (New Technology File System) and HPFS (High Performance File System) file systems . NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows HPFS or High Performance File System is a File system created specifically for the OS/2 Operating system to improve upon the limitations

Is supported by all versions of Microsoft Windows; it is an evolution of Microsoft's earlier operating system (MS-DOS, which, in turn, was based on 86-DOS). Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. 86-DOS was an operating system developed and marketed by Seattle Computer Products for its Intel 8086 -based computer kit FAT can ultimately trace its roots back to CP/M. CP/M (Control Program for Microcomputers is an Operating system originally created for Intel 8080 / 85 based Microcomputers by Gary Kildall Over the years various features have been added to it, inspired by similar features found on other file systems used by other operating systems such as Unix. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer

There are several versions of FAT used in Windows, these are: FAT12, FAT16 and FAT32; WinFS was supposed to have been included with Windows Vista. Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time Templateinfobox filesystem whilst covering all 3 file systems please make any style changes to both at the same time WinFS (short for Windows Future Storage) is the code name for a data storage and management system based on Relational databases developed by Windows Vista (ˈvɪstə is a line of Operating systems developed by Microsoft for use on Personal computers including home and business desktops

Fat Overview

FAT is by far the most simplistic of the file systems supported by Windows. The FAT file system is characterized by the file allocation table (FAT), which is really a table that resides at the very "top" of the volume. To protect the volume, two copies of the FAT are kept in case one becomes damaged. In addition, the FAT tables and the root directory must be stored in a fixed location so that the system's boot files can be correctly located.

A disk formatted with FAT is allocated in clusters, whose size are determined by the size of the volume. When a file is created, an entry is created in the directory and the first cluster number containing data is established. This entry in the FAT table either indicates that this is the last cluster of the file, or points to the next cluster.

Updating the FAT table is very important as well as time consuming. If the FAT table is not regularly updated, it can lead to data loss. It is time consuming because the disk read heads must be repositioned to the drive's logical track zero each time the FAT table is updated.

There is no organization to the FAT directory structure, and files are given the first open location on the drive. In addition, FAT supports only a few file attributes: read-only, hidden, system, and archive.

Older versions of the FAT file system (FAT12 and FAT16) had file name length limits, a limit on the number of entries in the root directory of the file system and had restrictions on the maximum size of FAT-formatted disks or partitions. Disk partitioning is the creation of separate divisions of a Hard disk drive using Partition editors Once a disk is divided into several partitions directories and Specifically, FAT12 and FAT16 had a limit of 8 characters for the file name, and 3 characters for the extension. This is commonly referred to as the 8.3 filename limit. An 83 filename (also called a short filename or SFN) is a Filename convention used by old versions of DOS and versions of Microsoft Windows VFAT, which was an extension to FAT12 and FAT16 introduced in Windows NT 3.5 and subsequently included in Windows 95, allowed long file names (LFN). Windows NT 35 is the second release of the Microsoft Windows NT Operating system. Long filenames ( LFN) spelled "long file names" by Microsoft are longer and therefore more descriptive Filenames supported by the Microsoft FAT32 also addressed many of the limits in FAT12 and FAT16, but remains limited compared to NTFS.

HPFS is only supported under Windows NT versions 3. HPFS or High Performance File System is a File system created specifically for the OS/2 Operating system to improve upon the limitations 1, 3. 5, and 3. 51. Windows NT 4. 0 cannot access HPFS partitions. It was also used by IBM's now defunct OS/2. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology OS/2 is a computer Operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively

HPFS Overview

The HPFS file system was first introduced with OS/2 1. 2 to allow for greater access to the larger hard drives that were then appearing on the market. Additionally, it was necessary for a new file system to extend the naming system, organization, and security for the growing demands of the network server market. HPFS maintains the directory organization of FAT, but adds automatic sorting of the directory based on filenames. Filenames are extended to up to 254 double byte characters. HPFS also allows a file to be composed of "data" and special attributes to allow for increased flexibility in terms of supporting other naming conventions and security. In addition, the unit of allocation is changed from clusters to physical sectors (512 bytes), which reduces lost disk space.

Under HPFS, directory entries hold more information than under FAT. As well as the attribute file, this includes information about the modification, creation, and access date and times. Instead of pointing to the first cluster of the file, the directory entries under HPFS point to the FNODE. FNODE (pronounced "eff node") occupies a single sector and contains control and access history information used internally by the file system extended attributes and Access control list the length and the first 15 characters of the name of the associated file or directory and an allocation structure. In Computer security, an access control list ( ACL) is a list of permissions attached to an object The FNODE can contain the file's data, or pointers that may point to the file's data or to other structures that will eventually point to the file's data.

HPFS attempts to allocate as much of a file in contiguous sectors as possible. This is done in order to increase speed when doing sequential processing of a file.

HPFS organizes a drive into a series of 8 MB bands, and whenever possible a file is contained within one of these bands. Between each of these bands are 2K allocation bitmaps, which keep track of which sectors within a band have and have not been allocated. Banding increases performance because the drive head does not have to return to the logical top (typically cylinder 0) of the disk, but to the nearest band allocation bitmap to determine where a file is to be stored.

Additionally, HPFS includes a couple of unique special data objects:

Super Block

The Super Block is located in logical sector 16 and contains a pointer to the FNODE of the root directory. One of the biggest dangers of using HPFS is that if the Super Block is lost or corrupted due to a bad sector, so are the contents of the partition, even if the rest of the drive is fine. It would be possible to recover the data on the drive by copying everything to another drive with a good sector 16 and rebuilding the Super Block. However, this is a very complex task.

Spare Block

The Spare Block is located in logical sector 17 and contains a table of "hot fixes" and the Spare Directory Block. Under HPFS, when a bad sector is detected, the "hot fixes" entry is used to logically point to an existing good sector in place of the bad sector. This technique for handling write errors is known as hot fixing.

Hot fixing is a technique where if an error occurs because of a bad sector, the file system moves the information to a different sector and marks the original sector as bad. This is all done transparent to any applications that are performing disk I/O (that is, the application never knows that there were any problems with the hard drive). Using a file system that supports hot fixing will eliminate error messages such as the FAT "Abort, Retry, or Fail?" error message that occurs when a bad sector is encountered.

Note: The version of HPFS that is included with Windows NT does not support hot fixing.

NTFS, introduced with the Windows NT operating system, allowed ACL-based permission control. NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Windows NT is a family of Operating systems produced by Microsoft, the first version of which was released in July 1993 In Computer security, an access control list ( ACL) is a list of permissions attached to an object Hard links, multiple file streams, attribute indexing, quota tracking, compression and mount-points for other file systems (called "junctions") are also supported, though not all these features are well-documented.

Unlike many other operating systems, Windows uses a drive letter abstraction at the user level to distinguish one disk or partition from another. For example, the path C:\WINDOWS represents a directory WINDOWS on the partition represented by the letter C. A path is the general form of a file or directory name giving a file's name and its unique location in a File system. The C drive is most commonly used for the primary hard disk partition, on which Windows is usually installed and from which it boots. This "tradition" has become so firmly ingrained that bugs came about in older versions of Windows which made assumptions that the drive that the operating system was installed on was C. The tradition of using "C" for the drive letter can be traced to MS-DOS, where the letters A and B were reserved for up to two floppy disk drives. Network drives may also be mapped to drive letters.

This was intended to be released with Windows Vista but it was canceled with no further information provided, except for that they are still working on WinFS. WinFS (short for Windows Future Storage) is the code name for a data storage and management system based on Relational databases developed by Windows Vista (ˈvɪstə is a line of Operating systems developed by Microsoft for use on Personal computers including home and business desktops

File systems under OpenVMS

Main article: Files-11

File systems under MVS [IBM Mainframe]

Main article: MVS#MVS filesystem

See also

• List of file systems
• Comparison of file systems
• Virtual file system
• File system fragmentation
• Distributed file system
• Filesystem API
• Physical and logical storage
• List of Unix programs
• Filename extension
• Disk sharing
• File system driver
• Garbage Collected Filesystem

References

• File System Forensic Analysis, Brian Carrier, Addison Wesley, 2005.

Further reading

• Local Filesystems for Windows
• Understanding File-Size Limits on NTFS and FAT
• Benchmarking Filesystems Part II using kernel 2. 6, by Justin Piszcz, Linux Gazette 122, January 2006
• Linux File System Benchmarks v2. 6 kernel with a stress on CPU usage
• Interview With the People Behind JFS, ReiserFS & XFS
• Large List of File System Summaries
• Filesystems (ext3, ReiserFS, XFS, JFS) comparison on Debian Etch
• Overview of some filesystems (outdated)
• Linux large file support (outdated)
• Sparse files support (outdated)
• Benchmarking Filesystems (outdated) by Justin Piszcz, Linux Gazette 102, May 2004
• Journaled Filesystem Benchmarks (outdated): A comparison of ReiserFS, XFS, JFS, ext3 & ext2
• Journal File System Performance (outdated): ReiserFS, JFS, and Ext3FS show their merits on a fast RAID appliance
• Linux Filesystem Benchmarks
• Jeremy Reimer. "From BFS to ZFS: past, present, and future of file systems", arstechnica. com, March 16, 2008. Events 597 BC - Babylonians capture Jerusalem, replace Jehoiachin with Zedekiah as king 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Retrieved on 2008-03-18. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 37 - The Roman Senate annuls Tiberius ' will and proclaims Caligula emperor  

External links

• Filesystems of Operating Systems
• Filesystem Specifications - Links & Whitepapers
• Interesting File System Projects