computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, an archive file is a

computer file A computer file is a computer resource for recording data in a computer storage device, primarily identified by its file name. Just as words can be written to paper, so can data be written to a computer file. Files can be shared with and trans ...

that is composed of one or more files along with

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 ...

. Archive files are used to

collect The collect ( ) is a short general prayer of a particular structure used in Christian liturgy. Collects appear in the liturgies of Catholic, Eastern Orthodox, Oriental Orthodox, Anglican, Methodist, Lutheran, and Presbyterian churches, among othe ...

multiple data files together into a single file for easier portability and storage, or simply to

compress compress is a Unix shell compression program based on the LZW compression algorithm. Compared to more modern compression utilities such as gzip and bzip2, compress performs faster and with less memory usage, at the cost of a significantly lo ...

files to use less storage space. Archive files often store

directory structure In computing, a directory structure is the way an operating system arranges Computer file, files that are accessible to the user. Files are typically displayed in a hierarchical tree structure. File names and extensions A filename is a string use ...

error detection and correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable commu ...

information, arbitrary comments, and sometimes use built-in

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can d ...

Applications

Portability

Archive files are particularly useful in that they store

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 ...

data and

within the contents of a particular file, and thus can be stored on systems or sent over channels that do not support the file system in question, only file contents – examples include sending a

over

email Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" mean ...

, files with names unsupported on the target file system due to length or characters, and retaining files' date and time information. Additionally, it facilitates transferring high numbers of small files such as resources of saved web pages, since a container file is transferred using a single file operation, whereas transferring many small files requires the computer to modify the file system structure for each file individually, making it considerably slower.

Software distribution

Beyond archival purposes, archive files are frequently used for packaging software for

distribution Distribution may refer to: Mathematics * Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a vari ...

, as software contents are often naturally spread across several files; the archive is then known as a ''package''. While the archival file format is the same, there are additional conventions about contents, such as requiring a

manifest file A manifest file in computing is a file containing metadata for a group of accompanying files that are part of a set or coherent unit. For example, the files of a computer program may have a manifest describing the name, version number, license and t ...

, and the resulting format is known as a package format. Examples include deb for

Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of De ...

, JAR for

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

, APK for Android, and self-extracting

Windows Installer Windows Installer (msiexec.exe, previously known as Microsoft Installer, codename Darwin) is a software component and application programming interface (API) of Microsoft Windows used for the installation, maintenance, and removal of software. ...

executables 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 instructions", as opposed to a data fil ...

Features

Features supported by various kinds of archives include: * converting

into data stored inside a file (e.g., file name, permissions, etc.) *

checksum A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...

s to detect errors *

data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressio ...

* file concatenation to store multiple files in a single file * file patches / updates (when recording changes since a previous archive) *

error correction code In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea ...

to fix errors * splitting a large file into many equal sized files for storage or transmission Some archive programs have self-extraction, self-installation, source volume and medium information, and package notes/description. The

file 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 ...

file header File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

of the archive file are indicators of the

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 format ...

used. Computer archive files are created by

file archiver A file archiver is a computer program that combines a number of files together into one archive file, or a series of archive files, for easier transportation or storage. File archivers may employ lossless data compression in their archive forma ...

software,

optical disc authoring software Optical disc authoring, including DVD and Blu-ray Disc authoring, is the process of assembling source material—video, audio or other data—into the proper logical volume format to then be recorded ("burned") onto an optical disc (typ ...

, and

disk image A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image i ...

software.

Archive formats

An archive format is the

of an archive file. Some formats are well-defined by their authors and have become conventions supported by multiple vendors and communities.

Types

* Archiving only formats store

and

concatenate In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In certain formalisations of concatenat ...

files. * Compression only formats only compress files. * Multi-function formats can store

, concatenate, compress, encrypt, create error detection and recovery information, and package the archive into self-extracting and self-expanding files. * Software packaging formats are used to create software packages that may be self-installing files. * Disk image formats are used to create

s of mass storage volumes.

Examples

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 ...

s used to distinguish different types of archives include zip,

rar RAR or Rar may refer to: * Radio acoustic ranging, a non-visual technique for determining a ship's position at sea * "rar", the ISO 639-2 code for the Cook Islands Māori language * RAR (file format), a proprietary compressed archive file format i ...

, 7z, and

tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...

, the first of which is the most widely implemented. Java also introduced a whole family of archive extensions such as jar and

war War is an intense armed conflict between states, governments, societies, or paramilitary groups such as mercenaries, insurgents, and militias. It is generally characterized by extreme violence, destruction, and mortality, using regular o ...

(''j'' is for Java and ''w'' is for web). They are used to exchange entire byte-code deployment. Sometimes they are also used to exchange source code and other text, HTML and XML files. By default they are all compressed.

Error detection and recovery

Archive files often include parity checks and other

s for

error detection In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communi ...

, for instance zip files use a

cyclic redundancy check A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to digital data. Blocks of data entering these systems get a short ''check value'' attached, based on ...

(CRC). RAR archives may include additional

error correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communi ...

data (called recovery records). Archive files that do not natively support recovery records can use separate

parchive Parchive (a portmanteau of parity archive, and formally known as Parity Volume Set Specification) is an erasure code system that produces par files for checksum verification of data integrity, with the capability to perform data recovery operatio ...

(PAR) files that allows for additional error correction and recovery of missing files in a multi-file archive.

References

"Application Note on the .ZIP file format"
official white paper published by PKWARE, Inc.
Tape Archive (.TAR) file format specification
excerpt from File Format List 2.0 by Max Maischein

from IBM Archives

from IBM Archives

External links

* {{Archive formats Computer files Computer archives Computer file systems Disk images Records management