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7Z file format (7-Zip archives)



extract 7z files

7Z archiving format was created for 7-Zip, a popular modern file archiver application written by Igor Pavlov, and released as freeware and Open Source software. 7-Zip (often incorrectly shortened in 7zip) was developed for Microsoft Windows platforms, and ported by p7zip (POSIX-7Zip) project team on Unix platforms.

7Z is capable of very high compression ratio through powerful compression algorithms (LZMA/LZMA2, PPMd, BZip2, optionally optimized Deflate), at cost of more memory and CPU intensive compression process - that however can take benefit of parallel computing on modern multicore CPUs.
On average test cases 7Z format improves compression ratio 30-70% better over classic ZIP format, and 6-7% better than RAR files (WinRar's native format, proprietary). 7Z compression compares favourably also with new WinZip's ZIPX format in most cases.
7Z format also provides native UTF-8 support for filenames, Rijndael/AES encryption, and volume spanning.

When is 7Z format recommended

in brief, .7z is a good choice anytime it is important to attain a superior compression ratio, and it is welcome the support for strong encyption to keep archived data private.

XZ extension identify a pure compression format (compresses a single file, without offering option of archiving multiple input file into a single output .xz file), it is based on LZMA/LZMA2 algorithm family, providing the usual 7z-like compression ratio (similar or higher compared to RAR), recently often used on TAR files.




Author Igor Pavlov, 1999

SPEED 7z extraction

Average. Computing intensive compression algorithms are balanced by efficient parallel programming implementation.


Very good. Comparable, often better than RAR compression, but inferior to state of art PAQ compressor.

ADVANCED OPTIONS encrypt 7z file
Good. Native support for AES encryption and UTF-8 encoding. Lacks recovery records option available for RAR format.

Work with 7Z files

PeaZip offers full read / write support for 7Z archives and XZ files, through the Open Source components from 7-Zip and p7zip projects (released under LGPL license, as PeaZip) to offer the same GUI frontend to create, browse, and extract 7Z archives under Windows and Linux operating systems.
The software can also manage password protected 7z archives (encrypt and decrypt), and convert files to / from 7z format.

As alternative, 7-Zip (on MS Windows systems) and p7zip (on Linux/BSD), both free and Open Source tools, are recommended for working with 7z file format.

Compress to 7Z format

Use one of the following procedures to add files / folders to a new or into an existing .7z file

  • Compress to 7z from system file explorer

    • Select files and folders and use context menu entry PeaZip, Add to archive: you will be prompted to archive creation screen, allowing to set compression settings, output destination, encryption (password protection), and other options.

    • Alternatively, use system context menu entry Add to .7Z in order to start compressing selected items without further interaction

  • From PeaZip

    • Select files and folders, and use Add button (or application's context menu entry of same name) to be prompted archive creation screen

    • Drag and drop files / folders from the system to a PeaZip instance; if you are browsing an existing archive you will be asked if you want to add files to the archive or create a new one

From main archive creation interface it is possible to apply encryption (recipient will need to enter a password to read/extract the archive), and to split file - set creation of multiple volumes declaring the maximum output size (spanned archive), in order to keep the output size below mandatory limits (e.g. upload or mail attachment size).
From "Advanced" tab, you can fine-tune compression settings: faster or higher compression level, algorithm, solid compression block size, compress open files, create self extracting archive (SFX) so recipient will not need an archive manager program to extract the data...

From "Console" and "Schedule" tab, the compression / backup task created in the GUI can be saved as command line script and (on Microsoft Windows operating system) scheduled for execution at fixed time intervals (hour, day of the week or of the month) - same apply for extraction / restore tasks, as the same tabs are featured in archive extraction interface.

Update existing 7Z archive

To update existing archive, adding files and folders, proceed as shown above for archive creation, but select an existing archive as output and chose add (always replace files in archive) or update (overwrite only older files in archive) "archive function" in advanced tab.
Easiest way to edit an existing archive is opening it in PeaZip and dragging files/folders to it, which will automatically activate update mode - can be changed into add mode in advanced tab.

To remove (delete) data from the archive, select items and press cancel or "Delete from archive" button. Deleted items will not be recoverable from recycle bin.
Entries in the context menu on the right of delete button allows to delete the entire archive in different supported ways (recycle, quick delete, overwrite with zeroes, secure delete shredding data to make the archive not recoverable)

Convert 7Z files

File converter procedure using Convert button extracts and then re-pack input archive files into any write-supported format (7z, arc, pea, tar, zip...), optionally keeping or discarding original archives.
This makes possible to convert any type supported for reading (e.g. ACE, CAB, RAR, TAR, ZIP...) into a new 7Z file (either one for each individual input archive, or consolidating all input items in a single output archive), as well as to convert existing 7Z file into another write-supported format.

Open and extract 7Z file

Use one of the procedures described below to open (browse and search inside the archive) and/or decompress .7Z archives or .XZ files

  • Decompress 7z files from the system

    • To view archive's content, open it in PeaZip with double click (if file extension is associated with the application), or using system context menu "Open as archive" entry, that will attempt to read any user provided file type regardless file type associations - this option is also available in PeaZip's context menu

    • Use context menu entry "Extract..." for full extraction screen GUI where to set output path and other options

    • Select one or more archives and use context menu entry Extract here or Extract here (to new folder) for quick extraction with no further confirmation

  • Within PeaZip

    • Extract button shows full featured archive extraction screen providing access to all options (password, set output path, open output path after extraction, keep or delete original archives, etc) and can send to extraction selected items only

    • Extract all to... button activate a simplified procedure only asking for output path

    • Simply drag & drop desired objects from the application to the system

    • Doubleclick on an archived file to open it in preview mode, i.e. to inspect its content before considering the need for real extraction

To extract a spanned (split) 7Z file, save all the parts in the same directory, then open as usual the first volume of the archive, which has .7Z.001 extension - subsequent volumes have progressively numbered file extensions (002, 003 etc).

Manage encrypted 7Z archives (AES256)

To create, or extract, an encrypted .7z file, enter the password in PeaZip clicking the padlock icon extract encrypted 7z file in the status bar (in the file/archive browser) or below output address field (in extraction or archiving interfaces), or click Tools > Enter password / keyfile in main menu, or press F9 accelerator key.

Encrypted items inside the archive are marked by * sign.

Please note 7z format supports file-level encryption so multiple passwords can be used in the same archive to encrypt different group of files - and consequently in this case different password must be provided to access each part of the archive, changing password entered in PeaZip.

"Keyfile" field is optional, leave it blank if you don't want to rely on two factor authentication - keyfile is the "what you have" element (needs to be handled safely), password (or passphrase) is the non-material  "what you know" element; both are needed for recovering the encrypted file content.
Use of keyfile increases security over password only encryption since also having access to the keyfile will be required to perform the extraction, eliminating the need of overly complex passwords to resist to social engineering profiling, and brute-forcing or dictionary attacks.

7Z files, more information

External online resources: 7-Zip official domain7zip software domain, p7zip projectp7zip POSIX port of 7-Zip for Unix and Unix-like operating systems, 7Z file format specifications7zip specifications, 7Z format Wikipedia entry7zip archive format, PPMdWikipedia prediction by partial matching and LZMA/LZMA2Lempel Ziv Markov chain algorithm data compression algorithms.

Topics and search suggestions: free 7-Zip and p7zip programs, what is .7z file extension wiki, how do I open 7z files (handle compress / decompress, read / write, view content, browse & search compressed data), edit existing 7z archive, extract 7z to new folder, drag and drop extraction, tar.xz

















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7 zip utility

PeaZip is a free cross-platform file archiver that provides an unified portable GUI for many Open Source technologies like 7-Zip, FreeArc, PAQ, UPX...
Create 7Z, ARC, BZ2, GZ, *PAQ, PEA, QUAD/BALZ, TAR, UPX, WIM, XZ, ZIP files
Open and extract over 180 archive types: ACE, ARJ, CAB, DMG, ISO, LHA, RAR, UDF, ZIPX files and more...
Features of PeaZip includes extract, create and convert multiple archives at once, create self-extracting archives, split/join files, strong encryption with two factor authentication, encrypted password manager, secure deletion, find duplicate files, calculate hashes, export job definition as script.

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