Editing File archiver

{{Short description|Utility software for combining files}}
{{refimprove|date=August 2016}}
In [[computing]], a '''file archiver''' is [[utility software]] that combines [[computer file|files]] into a single [[archive file]] {{endash}} or in less common cases, multiple files. 

A minimally designed archiver might concatenate the content of files along with file [[file name|name]] and length. A more advanced archiver stores additional [[metadata]], such as the [[Timestamping (computing)|timestamps]], [[file attribute]]s and access control information. An archiver might [[lossless data compression|compress]] input file content to reduce the size of the resulting archive.

The process of making an archive file is called ''archiving'' or ''packing''. Reconstructing the original files from an archive is called ''unarchiving'', ''unpacking'' or ''extracting''.

==Multics==
In the early days of computing, [[Multics]] provided the {{code|archive}} command {{endash}} a basic archiver without compression {{endash}} that descended from the [[Compatible Time-Sharing System|CTSS]] command of the same name. Multics also provided a [[magnetic tape]] archiver command, {{code|ta}}, which was perhaps the forerunner of the Unix command {{code|tar}}.<ref>{{cite web|last1=Van Vleck|first1=Tom|title=Multics Glossary - A|url=http://www.multicians.org/mga.html|website=multicians.org|access-date=Jan 6, 2016}}</ref>

==Unix==
As the [[Unix]] archive tools [[ar (Unix)|ar]], [[tar (file format)|tar]], and [[cpio]] do not provide compression, other tools, such as [[gzip]], [[bzip2]], or [[XZ Utils|xz]], are used to compress an archive file after it is created and to decompress before extracting. 

Not only does separating archiving from compressing follow the [[Unix philosophy]] that each tool should provide a single capability; not attempt to accomplish everything with one tool, it has the following advantages:
* As compression technology progresses, users may use a different compression tool without having to change how they use the archiver.
* [[Solid compression]] allows the compressor to take advantage of redundancy across the multiple archived files in order to achieve better compression than simply compressing each file individually.

Disadvantages include:
* Extracting a single file requires decompressing the entire file, which can be costly in terms of time and storage space; adding a file to an existing archive requires both decompression and recompression.
* The archive becomes damage-prone; corruption in any part of the file might cause all files to be lost.

A challenge:
* Compression cannot take advantage of redundancy between files unless the compression window is larger than the size of an individual file; for example, gzip uses [[DEFLATE]], which typically operates with a 32768-byte window, whereas bzip2 uses a [[Burrows–Wheeler transform]] roughly 27 times bigger; xz defaults to 8&nbsp;MiB but supports significantly larger windows.

Generally, [[filename extension|extensions]] are successively added to the file name to indicate the operations performed and therefore required to read a file. For example, archiving with {{code|tar}} command and then compressing with {{code|gzip}} command might be indicated with the <code>.tar.gz</code> extension.

==Windows==
Archiving tools on [[Microsoft Windows|Windows]] tend to have a [[graphical user interface]] (GUI) and to include compression {{endash}} including the built-in Windows feature as well as commonly used, third-party tools such as [[WinRAR]] and [[7-Zip]]. Unlike the built-in feature, WinRAR and 7-zip also provide a [[command-line interface]] (CLI) and [[solid compression]].

==See also==
* [[Comparison of file archivers]]
* [[Archive format]]
* [[List of archive formats]]
* [[Comparison of archive formats]]

==References==
{{Reflist}}


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[[Category:Computer storage systems]]
[[Category:Computer file systems]]
[[Category:Computer archives]]
[[Category:File archivers| ]]
[[Category:Utility software types]]