7z
| 7z | |
|---|---|
|
|
| File extension : |
.7z
|
| MIME type : | application / x-7z-compressed |
| Magic number : |
377A.BCAF.271C hex 7z \ xBC \ xAF '\ x1C ( ASCII-C notation ) |
| Developed by: | Igor Viktorovich Pavlov |
| Type: | Data compression |
| Container for: | any files |
| Website : | 7-zip.org/7z.html |
7z is a free file format for compressed archiving of files , which was introduced with 7-Zip by Igor Viktorovich Pavlov. The filename extension is "7z".
Compared to other formats, the Lempel-Ziv-Markow algorithm enables a very high data compression rate. In addition, 7z is characterized by an open architecture , the support of very large amounts of data and the support of Unicode as well as encryption according to the AES -256 standard. Due to the underlying architecture, the 7z format can easily be expanded to include additional data compression methods.
In addition to 7-Zip, the developer's reference program, numerous other programs support the creation and extraction of 7z files.
Main features
- Splitting files: Manually set the maximum size of the individual parts.
- Open architecture: This allows e.g. B. Support for any compression and conversion method can be added.
- Support of large files: With the support of file sizes of up to 16 exbibytes (approx. 16 billion gibibytes ), the size limitation should be irrelevant in practice at the present time and also in the long term (if one considers the history of hard disk capacities between 1980 and 2005 in the Extrapolated into the future , hard disks with a size of 1 EB will only be available from around 2035).
- Unicode file names
- Progressive compression
- Archive header compression
- Strong encryption: 7z implements strong encryption according to the Advanced Encryption Standard with key lengths of 256 bits (AES-256). The keys are generated in a process based on SHA-256 from a password specified by the user. The hashing is carried out 2 18 (262144) times in a row, which should make a brute force search for the key more difficult, since the time required for testing a key is multiplied (key strengthening) . File names can be encrypted with.
- Dictionary size depending on the system and work memory (RAM) up to 4 GiB at 64-bit operating systems
Data compression methods
Due to the open architecture of the 7z format, it can use any new compression method. The following methods are currently integrated in 7z:
| MethodID | description |
|---|---|
| LZMA | used by default, improved variant of the LZ77 algorithm |
| LZMA2 | Modified LZMA with the advantages of lower overhead for non-compressible data and better support for multithreading |
| PPMD | Dmitry Shkarin's PPMdH with small changes |
| BCJ | Converter for 32-bit x86 code |
| BCJ2 | Converter for 32-bit x86 code |
| bzip2 | Burrows-Wheeler transformation (BWT) followed by move-to-front and Huffman coding |
| Deflate | Modified LZ77 algorithm similar to ZIP |
Linux, Mac OS X, and other Unix-like systems
The disclosure of the format makes porting to other operating systems such as Linux possible. The open source reference implementation 7-Zip is a pure Windows program. The console version was ported to Linux as p7zip . However, the 7z format alone is not suitable for a real backup under Unix-like systems, as special files (devices, etc.) and file attributes such as owner and group of a file are not saved - in this case, prior archiving is recommended (e.g. with tar) and subsequent compression of the archive. The file attributes are generally irrelevant for the mere transfer of documents, so that a pure 7z file - created by is $ 7z a archivname.7z dateiensufficient.
7z is able to achieve a considerable acceleration of the compression on multi-core computers through multithreading (option -mmt=<number of CPUs> ). With regard to the 7z-compressed data stream, the program is not streaming-capable, i. H. the options -siand -soonly work for the uncompressed data (if this is required, you can switch to the related program xz , which can be used like gzip ).
The console version can now be integrated into numerous programs with a graphical user interface, including the preinstalled archive programs from Gnome ( File Roller ) and KDE ( Ark ). 7zX is available as a graphical tool under Mac OS X.
Web links
Individual evidence
- ↑ Markus Pilzwege: 7-Zip: Tip: Split large files. PC-WELT, January 29, 2009, accessed July 26, 2017 .
- ↑ a b 7z format
- ↑ Overview of various data compression methods , December 2, 2010 (English).
- ↑ p7zip - Linux Port (English).
- ↑ 7zX - Mac OS X Port (English).