Editing Bzip2 (section)

{{short description|File compression software}}
{{Redirect|Bzip|the protein domain|bZIP domain}}
{{Use dmy dates|date=December 2020}}
{{lowercase|title=bzip2}}
{{Infobox software
| name = bzip2
| logo = [[File:Bzip2-logo.png]]
| screenshot = 
| caption = 
| author = [[Julian Seward]]
| developer = Mark Wielaard, [[Federico Mena]], Micah Snyder
| released = {{Start date and age|df=yes|1996|07|18}}<ref>[https://www.ncbi.nlm.nih.gov/IEB/ToolBox/CPP_DOC/lxr/source/src/util/compress/bzip2/README bzip2/README], ''18 July 1996 (version 0.15)''</ref>
| latest release version = 1.0.8
| latest release date = {{Start date and age|df=yes|2019|07|13}}
| repo = https://gitlab.com/bzip2/bzip2/
| operating system = [[Cross-platform]]{{Which|date=February 2014}}
| genre = [[Data compression]]
| license = Modified zlib license<ref name="bzip2-license">{{cite web |last1=Seward |first1=Julian |
title=bzip2 and libbzip2 |url=https://sourceware.org/bzip2/manual/manual.html |website=sourceware.org}}</ref>
| website = {{URL|sourceware.org/bzip2/}}
}}

{{Infobox file format
| name          = bzip2
| extension     = <code>.bz2</code>
| mime          = <code>application/x-bzip2</code>
| uniform type  = public.bzip2-archive<ref>{{cite web |url=https://developer.apple.com/documentation/uniformtypeidentifiers/uttype/3551471-bz2 |title=bz2 |work=Apple Developer Documentation: Uniform Type Identifiers |publisher=[[Apple Inc]]}}</ref>
| owner         = [[Julian Seward]]
| type code     = <code>Bzp2</code>
| magic         = <code>BZh</code>
| genre         = [[Data compression]]
| container for = 
| contained by  = 
| extended from = 
| extended to   = 
| open          = Yes
}}

'''bzip2''' is a [[free and open-source]] [[computer file|file]] [[compression program]] that uses the [[Burrows–Wheeler transform|Burrows–Wheeler algorithm]]. It only compresses single files and is not a [[file archiver]]. It relies on separate external utilities such as <code>[[tar (computing)|tar]]</code> for tasks such as handling multiple files, and other tools for encryption, and archive splitting.

bzip2 was initially released in 1996 by [[Julian Seward]]. It compresses most files more effectively than older [[LZW]] and [[Deflate]] [[compression algorithms]] but is slower. bzip2 is particularly efficient for text data, and decompression is relatively fast. The algorithm uses several layers of compression techniques, such as [[run-length encoding]] (RLE), [[Burrows–Wheeler transform]] (BWT), [[move-to-front transform]] (MTF), and [[Huffman coding]]. 
bzip2 compresses data in blocks between 100 and 900 kB and uses the Burrows–Wheeler transform to convert frequently recurring character sequences into strings of identical letters. The move-to-front transform and Huffman coding are then applied. The compression performance is asymmetric, with decompression being faster than compression.

The algorithm has gone through multiple maintainers since its initial release, with Micah Snyder being the maintainer since June 2021. There have been some modifications to the algorithm, such as pbzip2, which uses [[Multithreading (software)|multi-threading]] to improve compression speed on multi-CPU and multi-core computers.

bzip2 is suitable for use in [[big data]] applications with [[cluster computing]] frameworks like [[Hadoop]] and [[Apache Spark]], as a compressed block can be decompressed without having to process earlier blocks.

The bundled ''bzip2recover'' utility tries recovering readable parts of damaged bzip2 data. It works by searching for individual blocks and dumping them into separate files.<ref>[http://web.archive.org/web/20060209035249/http://www.bzip.org/1.0.3/html/recovering.html 2.6 recovering data from damaged files - bzip.org]</ref>