Editing 7-Zip (section)

===7z===
{{Main|7z}}

By default, 7-Zip creates 7z-format archives with a <code>.7z</code> [[file extension]]. Each archive can contain multiple directories and files. As a ''container'' format, security or size reduction are achieved by looking for similarities throughout the data using a stacked combination of filters. These can consist of pre-processors, [[Data compression|compression algorithms]], and [[encryption]] filters.

The core 7z compression uses a variety of [[algorithm]]s, the most common of which are [[bzip2]], [[Prediction by partial matching|PPMd]], [[Lempel–Ziv–Markov chain algorithm#LZMA2_format|LZMA2]], and [[Lempel–Ziv–Markov chain algorithm|LZMA]]. Developed by Pavlov, LZMA is a relatively new system, making its debut as part of the 7z format. LZMA uses an LZ-based sliding dictionary of up to 3840 MB in size, backed by a [[Range encoding|range coder]].<ref>{{cite web|last=Diaz|first=Antonio Diaz |title=Lzip|url=http://lzip.nongnu.org/lzip.html |website=LZip.NonGNU.org |access-date=29 July 2010| archive-url= https://web.archive.org/web/20100729135045/http://lzip.nongnu.org/lzip.html| archive-date= 29 July 2010 | url-status= live}}</ref>

The native 7z [[file format]] is open and [[Modular programming|modular]]. [[File name]]s are stored as [[UTF-16|Unicode]].<ref>{{cite web|url=https://www.7-zip.org/7z.html|title=7z Format|last=Pavlov|first=Igor|website=7-zip.org|access-date=16 April 2017}}</ref>

In 2011, [[TopTenReviews]] found that the 7z compression was at least 17% better than [[Zip (file format)|ZIP]],<ref>{{cite web|url=http://file-compression-software-review.toptenreviews.com/7-zip-review.html|title=7-Zip 2011 – TopTenREVIEWS|archive-url=https://web.archive.org/web/20121025200631/http://file-compression-software-review.toptenreviews.com/7-zip-review.html|archive-date=25 October 2012}}</ref> and 7-Zip's own site has since 2002 reported that while compression ratio results are very dependent upon the data used for the tests, "Usually, 7-Zip compresses to 7z format 30–70% better than to zip format, and 7-Zip compresses to zip format 2–10% better than most other zip-compatible programs."<ref>{{cite web|url=http://www.7-zip.org/ |title=7-Zip (home page) |archive-url=https://web.archive.org/web/20020121054121/http://www.7-zip.org/ |archive-date=21 January 2002 |url-status=live |website=7-zip.org |author=Igor Pavlov }} Statement on compression performance very similar in January 2002 and April 2017.</ref>

The 7z file format specification is distributed with the program's source code, in the "doc" sub-directory.