What is a 7Z file?
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 in 7z
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
7z 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.
File Signature
7z files begin with signature bytes ‘7’ ‘z’ BC AF 27 1C.
AES Encryption
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.
Salient Features of 7z
7z is the new archive format, providing high compression ratio. The main features of 7z format include:
- Open file format under GNU Lesser General Public License that lets you use any compression and encryption method
- High compression ratio
- Strong AES-256 encryption
- Support for large files with size up to 16,000, 000, 000 GB (16 exbibytes)
- Unicode file names
- Solid compressing
- Archive headers compressing
