What is the 7Z file format?
Files with the .7z extension contain archived data that can be compressed and encrypted. The format supports pre-processing algorithms - BCJ, BCJ2, and Delta Encoding - which improve compression on specific data types such as executables.
An archive can be divided into multiple volumes; in that case the extensions of the specific parts follow the pattern name.7z.001, name.7z.002, etc. This format provides a high level of compression and is open, so various algorithms can be used for data compression.
The most popular algorithms used for compression in .7z archives:
- LZMA - based on the LZ77 algorithm, but providing significantly better compression ratios
- LZMA2 - an upgraded, parallelisable version of LZMA; the default algorithm in 7-Zip
- PPMd - algorithm based on PPMdH, introducing some small changes; effective on text data
- BZip2 - classic BWT algorithm
- Deflate - classic algorithm based on LZ77, also used in ZIP archives
.7z is the native format of the 7-Zip program. It supports AES-256 encryption, using derivative functions based on the SHA-256 algorithm in order to create a key based on the password provided by the user; optionally, file names within the archive can also be encrypted. The format also supports solid compression, where multiple files are compressed together as a single data stream for better ratios on similar files. It was developed in 1999 by Igor Pavlov, and every .7z file begins with the fixed 6-byte magic signature 37 7A BC AF 27 1C.
Security & safety
RISK: MEDIUMThe 7z format itself is safe, but archives are a classic malware-delivery wrapper: they hide the real file types until extracted and can slip past basic filters, so a .7z from an untrusted source may contain executables or scripts - scan the contents before running anything. Two specific cautions: (1) 7z archives can be AES-256 encrypted and password-protected, which is also used to evade antivirus scanning, so be wary of password-protected 7z files sent unsolicited; (2) self-extracting 7z .exe files run code by design - only open SFX archives from sources you trust. Extracting a normal 7z and inspecting its files first is the safe approach.
Format details
in a nutshellPrograms that open 7Z files
Windows4 apps
7-Zip
Open-source Right-click the .7z > 7-Zip > Extract Here (or Extract to folder). Free; also creates .7z archives. 
WinRAR
Paid Double-click to open and Extract To; WinRAR extracts (and can create) 7z archives. (7-Zip is the free choice.) 
PeaZip
Open-source Open the .7z and Extract; free, with a GUI and support for split/encrypted 7z archives. 
NanaZip
Open-source Modern 7-Zip fork with proper Windows 11 right-click integration; right-click > Extract. 
macOS2 apps
The Unarchiver
Free Set as default for .7z, then double-click to extract. Free on the Mac App Store; handles split 7z.
Keka
Free Drag the .7z onto Keka to extract; Keka also CREATES .7z (including password-protected). The go-to Mac archiver. 
Linux3 apps
PeaZip
Open-source GUI archiver for Linux; open the .7z and Extract, or compress to 7z with a password.
7-Zip / p7zip
Open-source Run '7z x archive.7z' (modern 7zip package) or the older p7zip. Creates and extracts 7z.
Ark / File Roller
Open-source Default GNOME/KDE archive managers; open the .7z and Extract (with p7zip backend installed). 
Android1 app
ZArchiver
Free Browse to the .7z, tap it, and Extract; supports split and password-protected 7z. Also creates 7z. Technical details
deep spec| File signature | 37 7A BC AF 27 1C - fixed 6-byte sequence at offset 0 in every .7z file |
| MIME type | application/x-7z-compressed |
| Default compression method | LZMA2 - parallelisable successor to LZMA, used by default in 7-Zip |
| Supported compression algorithms | LZMA, LZMA2, PPMd, BZip2, Deflate, Copy (store without compression) |
| Pre-processing filters | BCJ, BCJ2, Delta - improve compression ratios for x86/ARM executables and structured binary data |
| Encryption | AES-256 with SHA-256-based key derivation from a user-supplied password |
| Header encryption | Optional - hides file names, sizes, and timestamps from the archive directory listing |
| Solid compression | Supported - multiple files compressed as a single data stream for higher ratios on similar content |
| Split (multi-volume) archives | Supported - volume parts named sequentially as .7z.001, .7z.002, etc. |
| Maximum archive or file size | ~16 EiB theoretical limit (64-bit size fields throughout the format) |
| Integrity check | CRC-32 stored per file; CRC-64 available for header and stream integrity |
| Filename encoding | UTF-16 - supports any Unicode characters in paths and file names |
| Self-extracting archives (SFX) | Supported on Windows - .exe SFX modules wrap a .7z payload for extraction without 7-Zip installed |
| Typical compression advantage | Produces archives 30-70% smaller than ZIP on compressible data when using LZMA2 at comparable settings |
| Released | 1999 (7-Zip / 7z format) |
| Open standard | Yes · royalty-free |
| Specification | www.7-zip.org |
7Z conversions
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