Editing 7z (section)

=== Compression methods ===
The following compression methods are currently defined:

* [[LZMA]]&nbsp;– A variation of the [[LZ77 and LZ78|LZ77]] algorithm, using a sliding dictionary up to 4 GB in length for duplicate string elimination.  The LZ stage is followed by [[entropy coding]] using a [[Markov chain]]-based [[range encoding|range coder]] and [[binary tree]]s.
* [[Lempel–Ziv–Markov chain algorithm#LZMA2 format|LZMA2]]&nbsp;– modified version of LZMA providing better multithreading support and less expansion of incompressible data.<ref name="lzma2_source_code">{{cite web
| url         = http://jpf91.github.io/lzmad/api/lzma_lzma.html
| title       = lzma_.lzma
| work        = liblzma bindings
| first       = Lasse
| last        = Collin
| access-date  = 2010-01-03
| quote       = Compared to LZMA1, LZMA2 adds support for LZMA_SYNC_FLUSH, uncompressed chunks (smaller expansion when trying to compress uncompressible data), possibility to change lc/lp/pb in the middle of encoding, and some other internal improvements.
| archive-url= https://web.archive.org/web/20100208075245/https://www.google.com/codesearch/p?hl=en| archive-date= 8 February 2010 | url-status= live}}</ref>
* [[Bzip2]]&nbsp;– The standard [[Burrows–Wheeler transform]] algorithm.  Bzip2 uses two reversible transformations; BWT, then [[Move to front]] with [[Huffman coding]] for symbol reduction (the actual compression element).
<!-- [[Bzip]] used (stronger, but patented) [[arithmetic coding]].  No point mentioning this since 7z doesn't use it! -->
* [[Prediction by Partial Matching|PPMd]]&nbsp;– Dmitry Shkarin's 2002 PPMdH (PPMII (Prediction by Partial matching with Information Inheritance) and cPPMII (complicated PPMII)) with small changes: PPMII is an improved version of the 1984 [[PPM compression algorithm]] (prediction by partial matching).
* [[DEFLATE]]&nbsp;– Standard algorithm based on 32 kB [[LZ77 and LZ78|LZ77]] and [[Huffman coding]].  Deflate is found in several file formats including [[ZIP (file format)|ZIP]], [[gzip]], [[Portable Network Graphics|PNG]] and [[PDF]].  7-Zip contains a from-scratch DEFLATE encoder that frequently beats the ''de facto'' standard [[zlib]] version in compression size, but at the expense of CPU usage.

A suite of recompression tools called AdvanceCOMP contains a copy of the DEFLATE encoder from the 7-Zip implementation; these utilities can often be used to further compress the size of existing [[gzip]], [[ZIP (file format)|ZIP]], [[Portable Network Graphics|PNG]], or [[Multiple-image Network Graphics|MNG]] files.