7z is an archiving format for compressing files and folders with a high compression ratio. It is based on Open Source architecture which makes it possible to use any compression and encryption algorithms. The format is now supported by a number of software applications such as 7-ZIP which is publicly available for download and usage to manipulate .7z files. Files with .7z extension have mime-type application/x-7z-compressed.
Supported Compression Methods
7z can support any compression methods due to its open architecture. Below is a list of compression methods currently available and supported by 7z.
LZMA - Improved and optimized version of the LZ77 algorithm
LZMA2 - Improved version of LZMA
PPMD - Dmitry Shkarin’s PPMdH with small changes
BCJ - Converter for 32-bit x86 executables
BCJ2 - Converter for 32-bit x86 executables
BZIP2 - Standard BWT algorithm
Deflate - Standard LZ77-based algorithm
File Format Specifications
7z uses binary file format to store the compressed archives. The development and implementation of 7-ZIP archiver published the first appearance of the 7z file format. Its format specifications are accessible as plain text format under the “Docs” sub-directory in code repository of 7-ZIP which is publicly available under the GNU Lesser General Public License. LZMA is the default compression method used by 7z files.
7z files begin with signature bytes ‘7’ ‘z’ BC AF 27 1C.
The 7z file format supports 256-bit AES encryption with the ability to encrypt the filenames of a the archive. The key for encryption is user-defined, based on the SH-256 hash function.
7z is the new archive format, providing high compression ratio. The main features of 7z format include: