7z is the new archive format, providing high compression ratio. 7z has open architecture, so it can support any new compression methods. 7z also supports filters that improve compression ratio of main compression method. LZMA is default and general compression method of 7z format. High compression ratio — Variable dictionary size (up to 4 GB) — Compressing speed: about 2-8 MB/s on 4 GHz CPU (2 cpu threads version). Decompressing speed: about 30-100 MB/s on 4 GHz CPU (1 cpu thread). 7-Zip also supports encryption with AES-256 algorithm. This algorithm uses cipher key with length of 256 bits. To create that key 7-Zip uses derivation function based on SHA-256 hash algorithm. A key derivation function produces a derived key from text password defined by user. For increasing the cost of exhaustive search for passwords 7-Zip uses big number of iterations to produce cipher key from text password. 7z code is a part of 7-Zip program distributed under the GNU LGPL. You can download 7-Zip sources and binaries from Download Page.
n
Can I use 7-Zip in a commercial organization? Yes, 7-Zip is free software. You can use it on any computer. How can I set file associations to 7-Zip in Windows 7 and Windows Vista? You must run 7-Zip File Manager in administrator mode. Right-click the icon of 7-Zip File Manager, and then click Run as administrator. Then you can change file associations and some other options. Why 7z archives created by new version of 7-Zip can be larger than archives created by old version of 7-Zip? New versions of 7-Zip (starting from version 15.06) use another file sorting order by default for solid 7z archives. Old version of 7-Zip (before version 15.06) used file sorting «by type» («by extension»). Parameters field in «Add to archive» window, (or -mqs switch for command line version). You can get big difference in compression ratio for different sorting methods, if dictionary size is smaller than total size of files.
n
If there are similar files in different folders, the sorting «by type» can provide better compression ratio in some cases. Note that sorting «by type» has some drawbacks. For example, NTFS volumes use sorting order «by name», so if an archive uses another sorting, then the speed of some operations for files with unusual order can fall on HDD devices (HDDs have low speed for «seek» operations). Increase dictionary size. It can help when ‘qs’ is not used. Specify ‘qs’ in Parameters field (or use -mqs switch for command line version). If you think that unusual file order is not problem for you, and if better compression ratio with small dictionary is more important for you, use ‘qs’ mode. Why can’t 7-Zip open some ZIP archives? In 99% of these cases it means that the archive contains incorrect headers. Other ZIP programs can open some archives with incorrect headers, since these programs just ignore errors.
n
If you have such archive, please don’t call the 7-Zip developers about it. Instead try to find the program that was used to create the archive and inform the developers of that program that their software is not ZIP-compatible. There are also some ZIP archives that were encoded with methods unsupported by 7-Zip, for example, WAVPack (WinZip). Why can’t 7-Zip open some RAR archives? 7-Zip 9.20 supports RAR 2/3/4 formats only and doesn’t support RAR5 archives. But latest versions of 7-Zip supports RAR5 archives. Why does drag-and-drop archive extraction from 7-Zip to Explorer use temp files? 7-Zip doesn’t know folder path of drop target. Only Windows Explorer knows exact drop target. And Windows Explorer needs files (drag source) as decompressed files on disk. So 7-Zip extracts files from archive to temp folder and then 7-Zip notifies Windows Explorer about paths of these temp files. Then Windows Explorer copies these files to drop target folder.
n