7Z (7-Zip Archive)
An open archive format that squeezes files smaller than almost anything else, with optional AES-256 encryption baked in.
| Full name | 7-Zip Archive |
| Extension | .7z |
| MIME type | application/x-7z-compressed |
| Developer | Igor Pavlov |
| Released | 1999 |
| Type | Archive / lossless compression |
| Default compression | LZMA / LZMA2 |
| Encryption | AES-256 (optional, can cover filenames) |
What is a 7Z file?
7Z is an archive format created by Igor Pavlov and shipped as part of his free, open-source tool 7-Zip in 1999. It uses the LZMA compression algorithm, which typically produces smaller files than ZIP or RAR. The format is open and documented, so third-party tools can read and write it without any licensing fees.
A .7z file is a container that holds one or more files and folders in a single compressed package. It stores file data, names, sizes, and checksums together in a structured binary layout. The format supports solid compression, meaning multiple files are fed into a single compression stream, which raises the compression ratio when files share similar content. It can also encrypt the archive with AES-256, and optionally encrypt even the filenames so an attacker cannot see what is inside.
History
Igor Pavlov, a Russian developer, released 7-Zip and the 7z format in 1999. He published 7-Zip as free software and made the format specification publicly available so any developer could implement support. LZMA2, an improved variant of the original LZMA algorithm with better multithreading, later became the default compression method in newer versions of 7-Zip.
How it works
Every .7z file starts with a six-byte signature: the ASCII characters '7' and 'z' followed by four fixed bytes (0xBC 0xAF 0x27 0x1C). After the signature header comes a series of metadata blocks that describe the files, their sizes, checksums, compression codecs used, and optional encryption parameters. The actual compressed payload follows, with solid archives packing all file data into one continuous compressed stream. The end-of-archive block closes the structure and can itself be compressed to cut overhead.
What it is used for
- Distributing software or large datasets where download size matters
- Creating encrypted backups of sensitive documents
- Archiving many small, similar files where solid compression gives big gains
- Reducing storage costs for cold archives on disk or cloud storage
How to open it
7-Zip (free, Windows/Linux) opens .7z files natively, and The Unarchiver handles them on macOS. Most Linux distributions can install p7zip from their package manager to get command-line support.
Pros and cons
Strengths
- Very high compression ratios, often 30-70% better than ZIP on the same data
- AES-256 encryption with the option to hide filenames
- Free and open-source format with a public specification
- Supports files larger than 4 GB with no size limits
Trade-offs
- Slower to compress than ZIP or gzip, especially at high compression levels
- Native support is not built into Windows Explorer or macOS Finder without extra software
- Solid archives make extracting a single file slower because the full stream must be read
- Less universally supported than ZIP across older or embedded systems
Convert 7Z files
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7Z FAQ
Is 7Z better than ZIP?
For compression ratio, yes. 7Z typically produces archives 30-70% smaller than ZIP on the same files. ZIP has broader built-in support across operating systems, so 7Z is the better choice when size matters and the recipient can install 7-Zip or a compatible tool.
Can I open a .7z file without installing anything?
On Windows and macOS, you need a third-party tool. 7-Zip is the standard choice on Windows. On macOS, The Unarchiver is a free option from the App Store. Some Linux desktop environments handle .7z files automatically through the file manager.
Is the 7z format safe to use for encrypted backups?
Yes, 7Z uses AES-256 encryption with SHA-256 key derivation. It also lets you encrypt filenames, so nothing is revealed about the archive contents without the password. Use a strong, unique password because there is no password-recovery mechanism.
Why does extracting one file from a large .7z archive take so long?
If the archive was created with solid compression, all files share a single compressed stream. To reach a file in the middle, 7-Zip must decompress everything that comes before it. Creating the archive without solid compression avoids this, at the cost of a larger file size.