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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" dir="ltr"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="keywords" content="Bzip2,2006,7-Zip,7z,ASCII,Algorithm,Apache Ant,Apache License,Arithmetic coding,BSD license,Base 1" /> <link rel="shortcut icon" href="/favicon.ico" /> <link rel="search" type="application/opensearchdescription+xml" href="/w/opensearch_desc.php" title="Wikipedia (English)" /> <link rel="copyright" href="http://www.gnu.org/copyleft/fdl.html" /> <title>Bzip2 - Wikipedia, the free encyclopedia</title> <style type="text/css" media="screen,projection">/*<![CDATA[*/ @import "/skins-1.5/monobook/main.css?52"; /*]]>*/</style> <link rel="stylesheet" type="text/css" media="print" href="/skins-1.5/common/commonPrint.css?52" /> <link rel="stylesheet" type="text/css" media="handheld" href="/skins-1.5/monobook/handheld.css?52" /> <!--[if lt IE 5.5000]><style type="text/css">@import "/skins-1.5/monobook/IE50Fixes.css?52";</style><![endif]--> <!--[if IE 5.5000]><style type="text/css">@import "/skins-1.5/monobook/IE55Fixes.css?52";</style><![endif]--> <!--[if IE 6]><style type="text/css">@import "/skins-1.5/monobook/IE60Fixes.css?52";</style><![endif]--> <!--[if IE 7]><style type="text/css">@import "/skins-1.5/monobook/IE70Fixes.css?52";</style><![endif]--> <!--[if lt IE 7]><script type="text/javascript" src="/skins-1.5/common/IEFixes.js?52"></script> <meta http-equiv="imagetoolbar" content="no" /><![endif]--> <script type= "text/javascript">/*<![CDATA[*/var skin = "monobook";var stylepath = "/skins-1.5";var wgArticlePath = "/wiki/$1";var wgScriptPath = "/w";var wgServer = "http://en.wikipedia.org";var wgCanonicalNamespace = "";var wgCanonicalSpecialPageName = false;var wgNamespaceNumber = 0;var wgPageName = "Bzip2";var wgTitle = "Bzip2";var wgArticleId = "66255";var wgIsArticle = true;var wgUserName = null;var wgUserGroups = null;var wgUserLanguage = "en";var wgContentLanguage = "en";var wgBreakFrames = false;var wgCurRevisionId = "102478266";/*]]>*/</script> <script type="text/javascript" src="/skins-1.5/common/wikibits.js?52"><!-- wikibits js --></script> <script type="text/javascript" src="/w/index.php?title=-&action=raw&gen=js"><!-- site js --></script> <style type="text/css">/*<![CDATA[*/@import "/w/index.php?title=MediaWiki:Common.css&usemsgcache=yes&action=raw&ctype=text/css&smaxage=2678400";@import "/w/index.php?title=MediaWiki:Monobook.css&usemsgcache=yes&action=raw&ctype=text/css&smaxage=2678400";@import "/w/index.php?title=-&action=raw&gen=css&maxage=2678400";/*]]>*/</style> <!-- Head Scripts --> <script type="text/javascript" src="/skins-1.5/common/ajax.js?52"></script> </head><body class="mediawiki ns-0 ltr page-Bzip2"> <div id="globalWrapper"> <div id="column-content"> <div id="content"> <a name="top" id="top"></a> <div id="siteNotice"><script type="text/javascript" language="JavaScript"><!--document.writeln("\x3cdiv style=\"text-align:right; font-size:80%\"\x3eYour \x3cb\x3e\x3ca href=\"http://wikimediafoundation.org/wiki/Fundraising\" class=\"extiw\" title=\"wikimedia:Fundraising\"\x3econtinued donations\x3c/a\x3e\x3c/b\x3e keep Wikipedia running!\x26nbsp;\x26nbsp;\x26nbsp;\x26nbsp;\x3c/div\x3e\n");--></script></div> <h1 class="firstHeading">Bzip2</h1> <div id="bodyContent"> <h3 id="siteSub">From Wikipedia, the free encyclopedia</h3> <div id="contentSub"></div> <div id="jump-to-nav">Jump to: <a href="#column-one">navigation</a>, <a href="#searchInput">search</a></div> <!-- start content --> <table class="infobox" style="text-align: left; width: 23em; font-size: 90%;"><caption><b>bzip2</b></caption><tr><th style="white-space: nowrap;"><a href="/wiki/Filename_extension" title="Filename extension">File extension</a>:</th><td><code><tt>.bz2</tt>, <tt>.tar.bz2</tt>, <tt>.tbz2</tt>, .tb2</code></td></tr><tr><th style="white-space: nowrap;"><a href="/wiki/MIME" title="MIME">MIME type</a>:</th><td><code><tt>application/x-bzip</tt></code></td></tr><tr><th style="white-space: nowrap;"><a href="/wiki/Type_code" title="Type code">Type code</a>:</th><td><tt>Bzp2</tt></td></tr><tr><th style="white-space: nowrap;">Developed by:</th><td><a href="/wiki/Julian_Seward" title="Julian Seward">Julian Seward</a></td></tr><tr><th style="white-space: nowrap;">Type of format:</th><td><a href="/wiki/Data_compression" title="Data compression">data compression</a></td></tr><tr><td></td></tr></table><table class="infobox" cellspacing="5" style="width: 24em; font-size: 90%; text-align: left;"><caption style="font-size: 130%; font-weight: bold;">bzip2</caption><tr><th colspan="2" style="text-align: center;"></th></tr><tr><th><a href="/wiki/Software_development" title="Software development">Developer</a>:</th><td><a href="/wiki/Julian_Seward" title="Julian Seward">Julian Seward</a></td></tr><tr><th><a href="/wiki/Software_release" title="Software release">Latest release</a>:</th><td>1.0.4 / <a href="/wiki/December_20" title="December 20">December 20</a>, <a href="/wiki/2006" title="2006">2006</a></td></tr><tr><th><a href="/wiki/Operating_system" title="Operating system">OS</a>:</th><td><a href="/wiki/Cross-platform" title="Cross-platform">Cross-platform</a></td></tr><tr><th>Use:</th><td><a href="/wiki/Data_compression" title="Data compression">data compression</a></td></tr><tr><th><a href="/wiki/Software_license" title="Software license">License</a>:</th><td>Bzip2</td></tr><tr><th><a href="/wiki/Website" title="Website">Website</a>:</th><td><a href="http://www.bzip.org" class="external text" title="http://www.bzip.org" rel="nofollow">www.bzip.org</a></td></tr></table><div id="RealTitleBanner"><dl><dd><i>The correct title of this article is <b><span id="RealTitle">bzip2</span></b>. The initial letter is shown capitalized due to <a href="/wiki/Wikipedia:Naming_conventions_%28technical_restrictions%29#Lower_case_first_letter" title="Wikipedia:Naming conventions (technical restrictions)">technical restrictions</a>.</i></dd></dl></div><p><b>bzip2</b> is a <a href="/wiki/Free_software" title="Free software">free software</a>/<a href="/wiki/Open-source_software" title="Open-source software">open source</a> <a href="/wiki/Data_compression" title="Data compression">data compression</a> <a href="/wiki/Algorithm" title="Algorithm">algorithm</a> and program developed by <a href="/wiki/Julian_Seward" title="Julian Seward">Julian Seward</a>. Seward made the first public release of bzip2, version 0.15, in July 1996. The compressor's stability and popularity grew over the next several years, and Seward released version 1.0 in late 2000.</p><table id="toc" class="toc" summary="Contents"><tr><td><div id="toctitle"><h2>Contents</h2></div><ul><li class="toclevel-1"><a href="#Compression_efficiency"><span class="tocnumber">1</span> <span class="toctext">Compression efficiency</span></a></li><li class="toclevel-1"><a href="#Compression_stack"><span class="tocnumber">2</span> <span class="toctext">Compression stack</span></a></li><li class="toclevel-1"><a href="#File_format"><span class="tocnumber">3</span> <span class="toctext">File format</span></a></li><li class="toclevel-1"><a href="#Use"><span class="tocnumber">4</span> <span class="toctext">Use</span></a></li><li class="toclevel-1"><a href="#Implementations"><span class="tocnumber">5</span> <span class="toctext">Implementations</span></a></li><li class="toclevel-1"><a href="#See_also"><span class="tocnumber">6</span> <span class="toctext">See also</span></a></li><li class="toclevel-1"><a href="#External_links"><span class="tocnumber">7</span> <span class="toctext">External links</span></a></li><li class="toclevel-1"><a href="#References"><span class="tocnumber">8</span> <span class="toctext">References</span></a></li></ul></td></tr></table><p><script type="text/javascript">//<![CDATA[ if (window.showTocToggle) { var tocShowText = "show"; var tocHideText = "hide"; showTocToggle(); } //]]></script><a name="Compression_efficiency" id="Compression_efficiency"></a></p><h2><span class="editsection">[<a href="/w/index.php?title=Bzip2&action=edit&section=1" title="Edit section: Compression efficiency">edit</a>]</span> <span class="mw-headline">Compression efficiency</span></h2><p>bzip2 compresses most files more effectively than more traditional <a href="/wiki/Gzip" title="Gzip">gzip</a> or <a href="/wiki/ZIP_%28file_format%29" title="ZIP (file format)">ZIP</a> but is slower. In this manner it is fairly similar to other recent-generation compression algorithms. Unlike other formats such as <a href="/wiki/RAR" title="RAR">RAR</a> or ZIP (and similar to gzip), bzip2 is only a data compressor, not an archiver. The program itself has no facilities for multiple files, encryption or archive-splitting, in the <a href="/wiki/UNIX" title="UNIX">UNIX</a> tradition instead relying on separate external utilities such as <a href="/wiki/Tar_%28file_format%29" title="Tar (file format)">tar</a> and <a href="/wiki/GNU_Privacy_Guard" title="GNU Privacy Guard">GnuPG</a> for these tasks.</p><p>In some cases, bzip2 is surpassed by <a href="/wiki/7z" title="7z">7z</a> and RAR formats in terms of absolute compression efficiency. According to the author, bzip2 gets within ten to fifteen percent of the "best" class of compression algorithms currently known (<a href="/wiki/PPM_compression_algorithm" title="PPM compression algorithm">PPM</a>), although it is roughly twice as fast at compression and six times faster at decompression.</p><p>bzip2 uses the <a href="/wiki/Burrows-Wheeler_transform" title="Burrows-Wheeler transform">Burrows-Wheeler transform</a> to convert frequently recurring character sequences into strings of identical letters, and then applies a <a href="/wiki/Move-to-front_transform" title="Move-to-front transform">move-to-front transform</a> and finally <a href="/wiki/Huffman_coding" title="Huffman coding">Huffman coding</a>. In bzip2 the blocks are generally all the same size in plaintext, which can be selected by a command-line argument between 100<a href="/wiki/Kilobyte" title="Kilobyte">kB</a>鈥⌨️ 快捷键说明
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