Frequently Asked Questions (FAQ)

Can I use 7zip in a commercial organization?

Yes, 7zip is 100% free software for any purpose.
You can use it on any computer. You don’t need to register or pay for 7zip.

7Zip supports a lot of formats. Which archive format is better?

For better compression it’s recommended to use 7z format.
All other formats is worth using only when it is really necessary.

Why 7z archives created by new version of 7zip can be larger than archives created by old version of 7zip?

New versions of 7zip (starting from version 15.06) use another file sorting order by default for solid 7z archives.

Old version of 7zip (before version 15.06) used file sorting “by type” (“by extension”).

New version of 7zip supports two sorting orders:

  • sorting by name – default order.
  • sorting by type, if ‘qs‘ is specified in Parameters field in “Add to archive” window, (or -mqs switch for command line version).

You can get big difference in compression ratio for different sorting methods, if dictionary size is smaller than total size of files. If there are similar files in different folders, the sorting “by type” can provide better compression ratio in some cases.

Note that sorting “by type” has some drawbacks. For example, NTFS volumes use sorting order “by name”, so if an archive uses another sorting, then the speed of some operations for files with unusual order can fall on HDD devices (HDDs have low speed for “seek” operations).

You can increase compression ratio with the following methods:

  • Increase dictionary size. It can help when ‘qs’ is not used.
  • Specify ‘qs‘ in Parameters field (or use -mqs switch for command line version).

If you think that unusual file order is not problem for you, and if better compression ratio with small dictionary is more important for you, use ‘qs‘ mode.

Can 7zip open RAR5 archives?

Modern versions of 7zip (15.06 beta or later) supports RAR5 archives.

How can I set file associations to 7zip in Windows 7 and Windows Vista?

You must run 7zip File Manager in administrator mode. Right-click the icon of 7zip File Manager, and then click Run as administrator. Then you can change file associations and some other options.

Why 7zip can’t open some ZIP archives?

In the most of these cases it means that the archive contains incorrect headers. Other ZIP programs can open some archives with incorrect headers, since these programs just ignore errors.

If you have such archive, please don’t call the 7zip developers about it. Instead try to find the program that was used to create the archive and inform the developers of that program that their software is not ZIP-compatible.

There are also some ZIP archives that were encoded with methods unsupported by 7zip, for example, WAVPack (WinZip).

Why does drag-and-drop archive extraction from 7zip to Explorer use temp files?

7zip doesn’t know folder path of drop target. Only Windows Explorer knows exact drop target. And Windows Explorer needs files (drag source) as decompressed files on disk. So 7zip extracts files from archive to temp folder and then 7zip notifies Windows Explorer about paths of these temp files. Then Windows Explorer copies these files to drop target folder.

To avoid usage of temporary files, you can use Extract command of 7zip or drag-and-drop from 7zip to 7zip.

Why doesn’t the command line version add files without extensions to an archive?

You’re probably using a *.* wildcard. 7zip doesn’t use the operating system’s wildcard mask parser, and consequently treats *.* as any file that has an extension. To process all files you must use the * wildcard instead or omit the wildcard at all.

Why doesn’t -r switch work as expected?

In most cases you don’t need -r switch. 7zip can compress subfolders even without -r switch.

Example 1:

7z.exe a c:\a.7z "C:\Program Files"

compresses “C:\Program Files” completely, including all subfolders.

Example 2:

7z.exe a -r c:\a.7z "C:\Program Files"

searches and compresses “Program Files” in all subfolders of C:\ (for example, in “C:\WINDOWS”).
If you need to compress only files with some extension, you can use -r switch:

7z a -r c:\ c:\dir\*.txt 

compresses all *.txt files from folder c:\dir\ and all it’s subfolders.

How can I store full path of file in archive?

7zip stores only relative paths of files (without drive letter prefix). You can change current folder to folder that is common for all files that you want to compress and then you can use relative paths:

cd /D C:\dir1\
7z.exe a c:\a.7z file1.txt dir2\file2.txt

Why can’t 7zip use big dictionary in 32-bit Windows?

32-bit Windows allocates only 2 GB of virtual space per one application. Also that block of 2 GB can be fragmented (for example, by some DLL file), so 7zip can’t allocate one big contiguous block of virtual space. There are no such limitations in 64-bit Windows. So you can use any dictionary in Windows x64, if you have required amount of physical RAM.

How can I install 7zip in silent mode?

For exe installer: Use the “/S” parameter to do a silent installation and the /D=”C:\Program Files\7-Zip” parameter to specify the “output directory”. These options are case-sensitive.

For msi installer: Use the /q INSTALLDIR=”C:\Program Files\7-Zip” parameters.

How can I recover corrupted 7z archive?

There are some possible cases when archive is corrupted:

  • You can open archive and you can see the list of files, but when you press Extract or Test command, there are some errors: Data Error or CRC Error.
  • When you open archive, you get message “Can not open file ‘a.7z’ as archive”

It’s possible to recover some data. Read more about 7z recovering procedure.