Open RAR File

7Z File

7Z is an archive file format which allows usage of advanced compression methods like LZMA, LMZA2, BZip2, PPMd as well as an old DEFLATE method. 7Z is an open source format introduced and developed by Igor Pavlov. 7Z was introduced together with LZMA and LZMA2 compression methods also developed by Igor Pavlov. 7Z file format is implemented as part 7-Zip open source application.

LZMA is currently a default compression algorithm for 7Z format. It is a very efficient algorithm and provides high decompression performance and better compression ratio then DEFLATE method. Compression performance could be slow with LZMA so you may want to use another compression method if you need to compress quicker. But for scenarios like software or files distribution when compression speed is not as important LZMA could be the best choice.

7Z format also supports encryption using AES-256 algorithm based on a password provided by user. AES-256 is a very secure algorithm which makes extracting secure 7Z archive with long enough password virtually impossible.

Following applications currently support 7Z file format:

• 7-Zip
• WinRar
• PowerArchiver
• TUGZip
• IZArc

Similar to RAR compression application 7Z also provides a special method for executable file compression. These methods are referred to as BCJ and BCJ2. BCJ is a conversion and compression algorithm for x86 executables which normalizes addresses in them to absolute values. BCJ2 is an improved version of BCJ which adds additional executable file pre-processing to facilitate better compression.

In comparison to RAR format 7Z misses several important features like data recovery and support for storage of filesystem permission. Data recovery could be important for recovery of backup files from long-term storage devices which suffered data degradation. Filesystem permissions storage is also important for certain enterprise backup tasks.

Full 7-Zip sources are available at 7-Zip SourceForge page. 7Z files are transferred over e-mail or internet using application/x-7z-compressed multipurpose internet mail extensions (MIME) type.