A computer file is a
computer resource for recording
data
In the pursuit of knowledge, data (; ) is a collection of discrete Value_(semiotics), values that convey information, describing quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of sy ...
in a
computer storage device
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
The central processing unit (CPU) of a compute ...
, primarily identified by its
file name
A filename or file name is a name used to uniquely identify a computer file in a directory structure. Different file systems impose different restrictions on filename lengths.
A filename may (depending on the file system) include:
* name &ndas ...
. Just as words can be written to paper, so can data be written to a computer file. Files can be shared with and transferred between
computers and
mobile devices
A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...
via
removable media,
networks
Network, networking and networked may refer to:
Science and technology
* Network theory, the study of graphs as a representation of relations between discrete objects
* Network science, an academic field that studies complex networks
Mathematics
...
, or the
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
.
Different
types of computer files are designed for different purposes. A file may be designed to store an
Image, a written message, a
video
Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syst ...
, a
computer program
A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components.
A computer program ...
, or any wide variety of other kinds of data. Certain files can store multiple data types at once.
By using computer programs, a person can open, read, change, save, and close a computer file. Computer files may be reopened, modified, and
copied an arbitrary number of times.
Files are typically organized in a
file system, which tracks file locations on the disk and enables user access.
Etymology
![BRL61-IBM 305 RAMAC](https://upload.wikimedia.org/wikipedia/commons/d/d3/BRL61-IBM_305_RAMAC.jpeg)
The word "file" derives from the Latin ''filum'' ("a thread").
"File" was used in the context of computer storage as early as January 1940. In ''Punched Card Methods in Scientific Computation'', W. J. Eckert stated, "The first extensive use of the early Hollerith Tabulator in astronomy was made by
Comrie. He used it for building a table from successive differences, and for adding large numbers of harmonic terms". "Tables of functions are constructed from their differences with great efficiency, either as printed tables or as a
file of punched cards'."
In February 1950, in a
Radio Corporation of America
The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Com ...
(RCA) advertisement in ''
Popular Science
''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
'' magazine describing a new "memory" vacuum tube it had developed, RCA stated: "the results of countless computations can be kept 'on file' and taken out again. Such a 'file' now exists in a 'memory' tube developed at RCA Laboratories. Electronically it retains figures fed into calculating machines, holds them in storage while it memorizes new ones – speeds intelligent solutions through mazes of mathematics."
In 1952, "file" denoted, among other things, information stored on
punched card
A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...
s.
In early use, the underlying hardware, rather than the contents stored on it, was denominated a "file". For example, the
IBM 350
IBM manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive (HDD) and floppy disk drive (FDD) were invented by IBM and as such IBM's employees were responsible fo ...
disk drives were denominated "disk files". The introduction, circa 1961, by the
Burroughs MCP
The MCP (Master Control Program) is the operating system of the Burroughs small, medium and large systems, including the Unisys Clearpath/MCP systems.
MCP was originally written in 1961 in ESPOL (Executive Systems Problem Oriented Language). In ...
and the MIT
Compatible Time-Sharing System
The Compatible Time-Sharing System (CTSS) was the first general purpose time-sharing operating system. Compatible Time Sharing referred to time sharing which was compatible with batch processing; it could offer both time sharing and batch proces ...
of the concept of a "
file system" that managed several virtual "files" on one storage device is the origin of the contemporary denotation of the word. Although the contemporary "
register file
A register file is an array of processor registers in a central processing unit (CPU). Register banking is the method of using a single name to access multiple different physical registers depending on the operating mode. Modern integrated circuit- ...
" demonstrates the early concept of files, its use has greatly decreased.
File contents
On most modern
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s, files are organized into one-dimensional arrays of
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
s. The
format
Format may refer to:
Printing and visual media
* Text formatting, the typesetting of text elements
* Paper formats, or paper size standards
* Newspaper format, the size of the paper page
Computing
* File format, particular way that informatio ...
of a file is defined by its content since a file is solely a container for data.
On some platforms the format is indicated by its
filename extension
A filename extension, file name extension or file extension is a suffix to the name of a computer file (e.g., .txt, .docx, .md). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically d ...
, specifying the rules for how the bytes must be organized and interpreted meaningfully. For example, the bytes of a plain text file ( in Windows) are associated with either
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
or
UTF-8
UTF-8 is a variable-width encoding, variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit'' ...
characters, while the bytes of image, video, and audio files are interpreted otherwise. Most file types also allocate a few bytes for
metadata
Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive metadata – the descriptive ...
, which allows a file to carry some basic information about itself.
Some file systems can store arbitrary (not interpreted by the file system) file-specific data outside of the file format, but linked to the file, for example
extended attributes Extended file attributes are file system features that enable users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as permissions or ...
or
forks
In cutlery or kitchenware, a fork (from la, furca 'pitchfork') is a utensil, now usually made of metal, whose long handle terminates in a head that branches into several narrow and often slightly curved tines with which one can spear foods ei ...
. On other file systems this can be done via
sidecar file
Sidecar files, also known as buddy files or connected files, are computer files that store data (often metadata) which is not supported by the format of a source file.
There may be one or more sidecar files for each source file. There may also be ...
s or software-specific databases. All those methods, however, are more susceptible to loss of metadata than
container
A container is any receptacle or enclosure for holding a product used in storage, packaging, and transportation, including shipping.
Things kept inside of a container are protected on several sides by being inside of its structure. The term ...
and
archive file
In computing, an archive file is a computer file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compress ...
formats.
File size
At any instant in time, a file has a specific size, normally expressed as a number of
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
s, that indicates how much storage is occupied by the file. In most modern operating systems the size can be any non-negative whole number of bytes up to a system limit. Many older operating systems kept track only of the number of
blocks or
tracks occupied by a file on a physical storage device. In such systems, software employed other methods to track the exact byte count (e.g.,
CP/M
CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...
used a special control character,
Ctrl-Z
In computer data, a substitute character (␚) is a control character that is used to pad transmitted data in order to send it in blocks of fixed size, or to stand in place of a character that is recognized to be invalid, erroneous or unreprese ...
, to signal the end of text files).
The general definition of a file does not require that its size have any real meaning, however, unless the data within the file happens to correspond to data within a pool of persistent storage. A special case is a
zero byte file
A zero-byte file or zero-length file is a computer file containing no data; that is, it has a length or size of zero bytes.
Creation
There are many ways that could manually create a zero-byte file, for example, saving empty content in a text edi ...
; these files can be newly created files that have not yet had any data written to them, or may serve as some kind of
flag
A flag is a piece of fabric (most often rectangular or quadrilateral) with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration. The term ''flag'' is also used to refer to the graphic design empl ...
in the file system, or are accidents (the results of aborted disk operations). For example, the file to which the link points in a typical
Unix-like
A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
system probably has a defined size that seldom changes. Compare this with which is also a file, but as a
character special file
In Unix-like operating systems, a device file or special file is an interface to a device driver that appears in a file system as if it were an ordinary file. There are also special files in DOS, OS/2, and Windows. These special files allow ...
, its size is not meaningful.
Organization of data in a file
Information in a computer file can consist of smaller packets of information (often called "
records
A record, recording or records may refer to:
An item or collection of data Computing
* Record (computer science), a data structure
** Record, or row (database), a set of fields in a database related to one entity
** Boot sector or boot record, ...
" or "lines") that are individually different but share some common traits. For example, a payroll file might contain information concerning all the employees in a company and their payroll details; each record in the payroll file concerns just one employee, and all the records have the common trait of being related to payroll—this is very similar to placing all payroll information into a specific filing cabinet in an office that does not have a computer. A text file may contain lines of text, corresponding to printed lines on a piece of paper. Alternatively, a file may contain an arbitrary binary image (a
blob
Blob may refer to:
Science Computing
* Binary blob, in open source software, a non-free object file loaded into the kernel
* Binary large object (BLOB), in computer database systems
* A storage mechanism in the cloud computing platform M ...
) or it may contain an
executable
In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), instructi ...
.
The way information is grouped into a file is entirely up to how it is designed. This has led to a plethora of more or less standardized file structures for all imaginable purposes, from the simplest to the most complex. Most computer files are used by
computer program
A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components.
A computer program ...
s which create, modify or delete the files for their own use on an as-needed basis. The programmers who create the programs decide what files are needed, how they are to be used and (often) their names.
In some cases, computer programs manipulate files that are made visible to the computer user. For example, in a
word-processing program, the user manipulates document files that the user personally names. Although the content of the document file is arranged in a format that the word-processing program understands, the user is able to choose the name and location of the file and provide the bulk of the information (such as words and text) that will be stored in the file.
Many applications pack all their data files into a single file called an
archive file
In computing, an archive file is a computer file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compress ...
, using internal markers to discern the different types of information contained within. The benefits of the archive file are to lower the number of files for easier transfer, to reduce storage usage, or just to organize outdated files. The archive file must often be unpacked before next using.
Operations
The most basic operations that programs can perform on a file are:
* Create a new file
* Change the
access permissions and
attributes
Attribute may refer to:
* Attribute (philosophy), an extrinsic property of an object
* Attribute (research), a characteristic of an object
* Grammatical modifier, in natural languages
* Attribute (computing), a specification that defines a proper ...
of a file
*
Open
Open or OPEN may refer to:
Music
* Open (band), Australian pop/rock band
* The Open (band), English indie rock band
* ''Open'' (Blues Image album), 1969
* ''Open'' (Gotthard album), 1999
* ''Open'' (Cowboy Junkies album), 2001
* ''Open'' (YF ...
a file, which makes the file contents available to the program
*
Read
Read
Read may refer to:
* Reading, human cognitive process of decoding symbols in order to construct or derive meaning
* Read (automobile), an American car manufactured from 1913 to 1915
* Read (biology), an inferred sequence of base pairs of ...
data from a file
*
Write
Writing is a medium of human communication which involves the representation of a language through a system of physically inscribed, mechanically transferred, or digitally represented symbols.
Writing systems do not themselves constitute h ...
data to a file
*
Delete a file
*
Close
Close may refer to:
Music
* ''Close'' (Kim Wilde album), 1988
* ''Close'' (Marvin Sapp album), 2017
* ''Close'' (Sean Bonniwell album), 1969
* "Close" (Sub Focus song), 2014
* "Close" (Nick Jonas song), 2016
* "Close" (Rae Sremmurd song), 201 ...
a file, terminating the association between it and the program
*
Truncate
In mathematics and computer science, truncation is limiting the number of digits right of the decimal point.
Truncation and floor function
Truncation of positive real numbers can be done using the floor function. Given a number x \in \mathbb ...
a file, shortening it to a specified size within the file system without rewriting any content
Files on a computer can be created, moved, modified, grown, shrunk (
truncated), and deleted. In most cases, computer programs that are executed on the computer handle these operations, but the user of a computer can also manipulate files if necessary. For instance,
Microsoft Word
Microsoft Word is a word processing software developed by Microsoft. It was first released on October 25, 1983, under the name ''Multi-Tool Word'' for Xenix systems. Subsequent versions were later written for several other platforms includin ...
files are normally created and modified by the Microsoft Word program in response to user commands, but the user can also move,
rename
Rename may refer to:
* Rename (computing), rename of a file on a computer
* RENAME (command), command to rename a file in various operating systems
* Rename (relational algebra)
In relational algebra, a rename is a unary operation written as \r ...
, or
delete these files directly by using a
file manager program such as
Windows Explorer
File Explorer, previously known as Windows Explorer, is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file ...
(on Windows computers) or by
command lines (CLI).
In
Unix-like
A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
systems,
user space
A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour.
Kernel ...
programs do not operate directly, at a low level, on a file. Only the
kernel
Kernel may refer to:
Computing
* Kernel (operating system), the central component of most operating systems
* Kernel (image processing), a matrix used for image convolution
* Compute kernel, in GPGPU programming
* Kernel method, in machine learnin ...
deals with files, and it handles all user-space interaction with files in a manner that is transparent to the user-space programs. The
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
provides a level of
abstraction
Abstraction in its main sense is a conceptual process wherein general rules and concepts are derived from the usage and classification of specific examples, literal ("real" or "concrete") signifiers, first principles, or other methods.
"An abstr ...
, which means that interaction with a file from user-space is simply through its filename (instead of its
inode
The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attribute ...
). For example,
rm ''filename'' will not delete the file itself, but only a
link to the file. There can be many links to a file, but when they are all removed, the
kernel
Kernel may refer to:
Computing
* Kernel (operating system), the central component of most operating systems
* Kernel (image processing), a matrix used for image convolution
* Compute kernel, in GPGPU programming
* Kernel method, in machine learnin ...
considers that file's memory space free to be reallocated. This
free space
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
is commonly considered a security risk (due to the existence of
file recovery software). Any secure-deletion program uses kernel-space (system) functions to wipe the file's data.
File moves within a file system complete almost immediately because the data content does not need to be rewritten. Only the paths need to be changed.
Moving methods
There are two distinct implementations of file moves.
When moving files between devices or partitions, some file managing software deletes each selected file from the source directory individually after being transferred, while other software deletes all files at once only after every file has been transferred.
With the
mv
command for instance, the former method is used when selecting files individually, possibly with the use of
wildcards (example:
mv -n sourcePath/* targetPath
, while the latter method is used when selecting entire directories (example:
mv -n sourcePath targetPath
). Microsoft
Windows Explorer
File Explorer, previously known as Windows Explorer, is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file ...
uses the former method for
mass storage
In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. In general, the term is used as large in relation to contemporaneous hard disk drives, but it has been used large in relati ...
filemoves, but the latter method using
Media Transfer Protocol
The Media Transfer Protocol (MTP) is an extension to the Picture Transfer Protocol (PTP) communications protocol that allows media files to be transferred automatically to and from portable devices. Whereas PTP was designed for downloading phot ...
, as described in .
The former method (individual deletion from source) has the benefit that space is released from the source device or partition imminently after the transfer has begun, meaning after the first file is finished. With the latter method, space is only freed after the transfer of the entire selection has finished.
If an incomplete file transfer with the latter method is aborted unexpectedly, perhaps due to an unexpected power-off, system halt or disconnection of a device, no space will have been freed up on the source device or partition. The user would need to merge the remaining files from the source, including the incompletely written (truncated) last file.
With the individual deletion method, the file moving software also does not need to cumulatively keep track of all files finished transferring for the case that a user manually aborts the file transfer. A file manager using the latter (afterwards deletion) method will have to only delete the files from the source directory that have already finished transferring.
Identifying and organizing
![FileFolders](https://upload.wikimedia.org/wikipedia/commons/9/92/FileFolders.svg)
In modern computer systems, files are typically accessed using names (
filename
A filename or file name is a name used to uniquely identify a computer file in a directory structure. Different file systems impose different restrictions on filename lengths.
A filename may (depending on the file system) include:
* name &ndas ...
s). In some operating systems, the name is associated with the file itself. In others, the file is anonymous, and is pointed to by links that have names. In the latter case, a user can identify the name of the link with the file itself, but this is a false analogue, especially where there exists more than one link to the same file.
Files (or links to files) can be located in directories. However, more generally, a
directory
Directory may refer to:
* Directory (computing), or folder, a file system structure in which to store computer files
* Directory (OpenVMS command)
* Directory service, a software application for organizing information about a computer network's u ...
can contain either a list of files or a list of links to files. Within this definition, it is of paramount importance that the term "file" includes directories. This permits the existence of directory hierarchies, i.e., directories containing sub-directories. A name that refers to a file within a directory must be typically unique. In other words, there must be no identical names within a directory. However, in some operating systems, a name may include a specification of type that means a directory can contain an identical name for more than one type of object such as a directory and a file.
In environments in which a file is named, a file's name and the path to the file's directory must uniquely identify it among all other files in the computer system—no two files can have the same name and path. Where a file is anonymous, named references to it will exist within a namespace. In most cases, any name within the namespace will refer to exactly zero or one file. However, any file may be represented within any namespace by zero, one or more names.
Any string of characters may be a well-formed name for a file or a link depending upon the context of application. Whether or not a name is well-formed depends on the type of computer system being used. Early computers permitted only a few letters or digits in the name of a file, but modern computers allow long names (some up to 255 characters) containing almost any combination of
unicode
Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
letters or unicode digits, making it easier to understand the purpose of a file at a glance. Some computer systems allow file names to contain spaces; others do not. Case-sensitivity of file names is determined by the
file system. Unix file systems are usually case sensitive and allow user-level applications to create files whose names differ only in the case of characters.
Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
supports multiple file systems, each with different policies regarding case-sensitivity. The common
FAT
In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food.
The term often refers spec ...
file system can have multiple files whose names differ only in case if the user uses a
disk editor
A disk editor is a computer program that allows its user to read, edit, and write raw data (at character or hexadecimal, byte-levels) on disk drives (e.g., hard disks, USB flash disks or removable media such as a floppy disks); as such, they ...
to edit the file names in the
directory entries. User applications, however, will usually not allow the user to create multiple files with the same name but differing in case.
Most computers organize files into hierarchies using folders, directories, or catalogs. The concept is the same irrespective of the terminology used. Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building a tree-like structure in which one "master folder" (or "root folder" — the name varies from one operating system to another) can contain any number of levels of other folders and files. Folders can be named just as files can (except for the root folder, which often does not have a name). The use of folders makes it easier to organize files in a logical way.
When a computer allows the use of folders, each file and folder has not only a name of its own, but also a path, which identifies the folder or folders in which a file or folder resides. In the path, some sort of special character—such as a slash—is used to separate the file and folder names. For example, in the illustration shown in this article, the path uniquely identifies a file called in a folder called , which in turn is contained in a folder called . The folder and file names are separated by slashes in this example; the topmost or root folder has no name, and so the path begins with a slash (if the root folder had a name, it would precede this first slash).
Many computer systems use
extensions
Extension, extend or extended may refer to:
Mathematics
Logic or set theory
* Axiom of extensionality
* Extensible cardinal
* Extension (model theory)
* Extension (predicate logic), the set of tuples of values that satisfy the predicate
* Ex ...
in file names to help identify what they contain, also known as the file type. On Windows computers, extensions consist of a dot (period) at the end of a file name, followed by a few letters to identify the type of file. An extension of identifies a text file; a extension identifies any type of document or documentation, commonly in the
Microsoft Word
Microsoft Word is a word processing software developed by Microsoft. It was first released on October 25, 1983, under the name ''Multi-Tool Word'' for Xenix systems. Subsequent versions were later written for several other platforms includin ...
file format
A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free.
Some file formats ...
;
and so on. Even when extensions are used in a computer system, the degree to which the computer system recognizes and heeds them can vary; in some systems, they are required, while in other systems, they are completely ignored if they are presented.
Protection
Many modern computer systems provide methods for protecting files against accidental and deliberate damage. Computers that allow for multiple users implement
file permissions
Most file systems include attributes of files and directories that control the ability of users to read, change, navigate, and execute the contents of the file system. In some cases, menu options or functions may be made visible or hidden dependin ...
to control who may or may not modify, delete, or create files and folders. For example, a given user may be granted only permission to read a file or folder, but not to modify or delete it; or a user may be given permission to read and modify files or folders, but not to execute them. Permissions may also be used to allow only certain users to see the contents of a file or folder. Permissions protect against unauthorized tampering or destruction of information in files, and keep private information confidential from unauthorized users.
Another protection mechanism implemented in many computers is a ''read-only flag.'' When this flag is turned on for a file (which can be accomplished by a computer program or by a human user), the file can be examined, but it cannot be modified. This flag is useful for critical information that must not be modified or erased, such as special files that are used only by internal parts of the computer system. Some systems also include a ''
hidden flag'' to make certain files invisible; this flag is used by the computer system to hide essential system files that users should not alter.
Storage
Any file that has any useful purpose must have some physical manifestation. That is, a file (an abstract concept) in a real computer system must have a real physical analogue if it is to exist at all.
In physical terms, most computer files are stored on some type of data storage device. For example, most
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s store files on a
hard disk
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...
. Hard disks have been the ubiquitous form of
non-volatile
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typic ...
storage since the early 1960s.
[Magnetic Storage Handbook 2nd Ed., Section 2.1.1, Disk File Technology, Mee and Daniel, (c)1990,] Where files contain only temporary information, they may be stored in
RAM
Ram, ram, or RAM may refer to:
Animals
* A male sheep
* Ram cichlid, a freshwater tropical fish
People
* Ram (given name)
* Ram (surname)
* Ram (director) (Ramsubramaniam), an Indian Tamil film director
* RAM (musician) (born 1974), Dutch
* ...
. Computer files can be also stored on other media in some cases, such as
magnetic tape
Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magne ...
s,
compact disc
The compact disc (CD) is a Digital media, digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then rele ...
s,
Digital Versatile Disc
The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any ki ...
s,
Zip drive
The Zip drive is a removable floppy disk storage system that was introduced by Iomega in late 1994. Considered medium-to-high-capacity at the time of its release, Zip disks were originally launched with capacities of 100 MB, then 250 ...
s,
USB flash drive
A USB flash drive (also called a thumb drive) is a data storage device that includes flash memory with an integrated USB interface. It is typically removable, rewritable and much smaller than an optical disc. Most weigh less than . Since firs ...
s, etc. The use of
solid state drives
A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is a ...
is also beginning to rival the hard disk drive.
In Unix-like operating systems, many files have no associated physical storage device. Examples are and most files under directories , and . These are virtual files: they exist as objects within the operating system kernel.
As seen by a running user program, files are usually represented either by a
file control block
A File Control Block (FCB) is a file system structure in which the state of an open file is maintained. A FCB is managed by the operating system, but it resides in the memory of the program that uses the file, not in operating system memory. This ...
or by a
file handle
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier ( handle) for a file or other input/output resource, such as a pipe or network socket.
File descriptors typically hav ...
. A file control block (FCB) is an area of memory which is manipulated to establish a filename etc. and then passed to the operating system as a parameter; it was used by older IBM operating systems and early PC operating systems including
CP/M
CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...
and early versions of
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
. A file handle is generally either an
opaque data type
In computer science, an opaque data type is a data type whose concrete data structure is not defined in an interface. This enforces information hiding, since its values can only be manipulated by calling subroutines that have access to the missing ...
or an integer; it was introduced in around 1961 by the
ALGOL-based Burroughs MCP
The MCP (Master Control Program) is the operating system of the Burroughs small, medium and large systems, including the Unisys Clearpath/MCP systems.
MCP was originally written in 1961 in ESPOL (Executive Systems Problem Oriented Language). In ...
running on the
Burroughs B5000
The Burroughs Large Systems Group produced a family of large 48-bit mainframes using stack machine instruction sets with dense syllables.E.g., 12-bit syllables for B5000, 8-bit syllables for B6500 The first machine in the family was the B5000 in ...
but is now ubiquitous.
File corruption
When a file is said to be corrupted, it is because its contents have been saved to the computer in such a way that they cannot be properly read, either by a human or by software. Depending on the extent of the damage, the original file can sometimes be
recovered, or at least partially understood.
A file may be created corrupt, or it may be corrupted at a later point through overwriting.
There are many ways by which a file can become corrupted. Most commonly, the issue happens in the process of
writing
Writing is a medium of human communication which involves the representation of a language through a system of physically Epigraphy, inscribed, Printing press, mechanically transferred, or Word processor, digitally represented Symbols (semiot ...
the file to a
disk
Disk or disc may refer to:
* Disk (mathematics), a geometric shape
* Disk storage
Music
* Disc (band), an American experimental music band
* ''Disk'' (album), a 1995 EP by Moby
Other uses
* Disk (functional analysis), a subset of a vector sp ...
.
For example, if an
image-editing program unexpectedly
crashes while saving an image, that file may be corrupted because the program could not save its entirety. The program itself might warn the user that there was an error, allowing for another attempt at saving the file.
Some other examples of reasons for which files become corrupted include:
* The computer itself
shutting down unexpectedly (for example, due to a power loss) with open files, or files in the process of being saved;
* A
download
In computer networks, download means to ''receive'' data from a remote system, typically a server such as a web server, an FTP server, an email server, or other similar system. This contrasts with uploading, where data is ''sent to'' a remote s ...
being interrupted before it was completed;
* Due to a
bad sector A bad sector in computing is a disk sector on a disk storage unit that is permanently damaged. Upon taking damage, all information stored on that sector is lost. When a bad sector is found and marked, the operating system like Windows or Linux will ...
on the
hard drive
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...
;
* The user removing a
flash drive
A flash drive is a portable computer drive that uses flash memory. Flash drives are the larger memory modules consisting of a number of flash chips. A flash chip is used to read the contents of a single cell, but it can write entire block of cell ...
(such as a
USB stick
A USB flash drive (also called a thumb drive) is a data storage device that includes flash memory with an integrated USB interface. It is typically removable, rewritable and much smaller than an optical disc. Most weigh less than . Since first ...
) without properly
unmounting (commonly referred to as "safely removing");
* Malicious software, such as a
computer virus
A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. If this replication succeeds, the affected areas are then said to be "infected" with a compu ...
;
* A flash drive becoming too old.
Although file corruption usually happens accidentally, it may also be done on purpose as a mean of
procrastination
Procrastination is the action of unnecessarily and voluntarily delaying or postponing something despite knowing that there will be negative consequences for doing so. The word has originated from the Latin word ''procrastinatus'', which itself evo ...
, as to fool someone else into thinking an assignment was ready at an earlier date, potentially gaining time to finish said assignment. There are services that provide on demand file corruption, which essentially fill a given file with random data so that it cannot be opened or read, yet still seems legitimate.
One of the most effective countermeasures for unintentional file corruption is
backing up
Reversing (also known as backing up) is the process of driving a vehicle in the reverse direction in order to maneuver. Rear view mirrors are somewhat standard equipment for this endeavor. Extremely large or luxury vehicles may have in addition t ...
important files.
In the event of an important file becoming corrupted, the user can simply replace it with the backed up version.
Backup
When computer files contain information that is extremely important, a ''
back-up
In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "wikt:back u ...
'' process is used to protect against disasters that might destroy the files. Backing up files simply means making copies of the files in a separate location so that they can be restored if something happens to the computer, or if they are deleted accidentally.
There are many ways to back up files. Most computer systems provide utility programs to assist in the back-up process, which can become very time-consuming if there are many files to safeguard. Files are often copied to removable media such as writable CDs or cartridge tapes. Copying files to another hard disk in the same computer protects against failure of one disk, but if it is necessary to protect against failure or destruction of the entire computer, then copies of the files must be made on other media that can be taken away from the computer and stored in a safe, distant location.
The
grandfather-father-son backup
A backup rotation scheme is a system of backing up data to computer media (such as tapes) that minimizes, by re-use, the number of media used. The scheme determines how and when each piece of removable storage is used for a backup job and how lon ...
method automatically makes three back-ups; the grandfather file is the oldest copy of the file and the son is the current copy.
File systems and file managers
The way a computer organizes, names, stores and manipulates files is globally referred to as its ''
file system.'' Most computers have at least one file system. Some computers allow the use of several different file systems. For instance, on newer MS Windows computers, the older FAT-type file systems of
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
and old versions of Windows are supported, in addition to the
NTFS
New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred fil ...
file system that is the normal file system for recent versions of Windows. Each system has its own advantages and disadvantages. Standard FAT allows only eight-character file names (plus a three-character extension) with no spaces, for example, whereas NTFS allows much longer names that can contain spaces. You can call a file "" in NTFS, but in FAT you would be restricted to something like (unless you were using
VFAT
File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by c ...
, a FAT extension allowing long file names).
File manager
A file manager or file browser is a computer program that provides a user interface to manage files and folders. The most common operations performed on files or groups of files include creating, opening (e.g. viewing, playing, editing or pr ...
programs are utility programs that allow users to manipulate files directly. They allow you to move, create, delete and rename files and folders, although they do not actually allow you to read the contents of a file or store information in it. Every computer system provides at least one file-manager program for its native file system. For example,
File Explorer
File Explorer, previously known as Windows Explorer, is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file ...
(formerly Windows Explorer) is commonly used in Microsoft Windows operating systems, and
Nautilus
The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.
It comprises six living species in t ...
is common under several distributions of Linux.
See also
*
Block (data storage)
In computing (specifically data transmission and data storage), a block, sometimes called a physical record, is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a ''block size''. Data thus ...
*
Computer file management
A file manager or file browser is a computer program that provides a user interface to manage files and folders. The most common operations performed on files or groups of files include creating, opening (e.g. viewing, playing, editing or pr ...
*
Data hierarchy Data hierarchy refers to the systematic organization of data, often in a hierarchical form. Data organization involves characters, fields, records, files and so on. This concept is a starting point when trying to see what makes up data and whether d ...
*
File camouflage
Steganography ( ) is the practice of representing information within another message or physical object, in such a manner that the presence of the information is not evident to human inspection. In computing/electronic contexts, a computer file, ...
*
File copying
In digital file management, copying is a file operation that creates a new file which has the same content as an existing file. Computer operating systems include file copying methods to users, with operating systems with graphical user interface ...
*
File conversion
Data conversion is the conversion of computer data from one format to another. Throughout a computer environment, data is encoded in a variety of ways. For example, computer hardware is built on the basis of certain standards, which requires th ...
*
File deletion
File deletion is the removal of a computer file, file from a computer's file system.
All operating systems include commands for deleting files (rm (Unix), rm on Unix, del (command), era in CP/M and DR-DOS, del (command), del/del (command), eras ...
*
File directory
In computing, a directory is a file system cataloging structure which contains references to other computer files, and possibly other directories. On many computers, directories are known as folders, or drawers, analogous to a workbench or the tr ...
*
File manager
A file manager or file browser is a computer program that provides a user interface to manage files and folders. The most common operations performed on files or groups of files include creating, opening (e.g. viewing, playing, editing or pr ...
*
File system
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
* Filename
* Flat-file database
* Object composition
* Soft copy
References
External links
*
*
{{Computer files
Computer files,
Computer file systems, File
Inter-process communication