Frequently Asked Questions (FAQ)

The step to set file associations to 7-Zip in Windows 7 and Windows Vista?

Step 1:  In administrator mode, run the 7 Zip

Step 2:  Right-click the icon of 7-Zip File Manager,

Step 3:  Click-> Run as administrator.

Step 4: Change the file associations and some other options.

Why the archives created by 7 Zip new version is larger than the old version of 7 Zip?

Old version of 7-Zip (before 15.06 version )

  • File sorting “by type” (“by extension”).

The new version of 7-Zip supports two sorting orders:

  • sorting by name – default order.
  • sorting by type,
  • Case 1:  ‘qs’ is specified in the Parameters field in “Add to archive” window,
  • Case 2:  mqs switch for the command-line version

The compression ratio is different for different sorting methods. For example, for similar files in separate folders. The sorting is “by type” provides a better compression ratio in a few cases.

Increase the  compression ratio with the following methods:

  • The increase dictionary siz is  helpful  when ‘qs’ not used.
  • Specify ‘qs’ in the Parameters field
  • Else  use -mqs switch-> command-line version

use ‘qs’ mode  for the better compression in a small dictionary

Why can’t 7-Zip open some ZIP archives?

If you see the message “Can not open file ’a.7z’ as archive”, which implies that 7-Zip can’t open some header from the start or the end of the archive. In such cases, open the file in a hex editor and  Start Header and End Header.

Some ZIP archives were encoded with methods unsupported by 7-Zip, for example, WinZip.

Why can’t 7-Zip open some RAR archives?

7-Zip 9.20 doesn’t support RAR5 archives. But the latest versions of 7-Zip supports RAR5 archives.

Why doesn’t -r switch work as expected?

7-Zip can compress subfolders 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”

search and compresses the -> “Program Files” in all subfolders of C:\

If you want  to compress only files with some extension,  user-r switch:

  7z a -r c:\ c:\dir\*.txt

compresses all *.txt files from folder c:\dir\   with its subfolders.

How to store the full path of a file in an archive?

Change the current folder to folder which is  common for all files that you want to compress and  use  the relative paths:

  cd /D C:\dir1\

7z.exe a c:\a.7z file1.txt dir2\file2.txt


Why  7-Zip  unable to use big dictionary in 32-bit Windows?

For one application 32-bit window allocates only 2 GB of Virtual space, and the DLL file can fragment the block of 2 GB. Hence 7-Zip can’t assign one contiguous block of virtual space, but no such limitations exist with 64-bit Windows.

How to install 7-Zip in silent mode?

For exe installer:

· Use the “/S” ( for silent installation)

· the /D=”C:\Program Files\7-Zip

Note: All are case-sensitive.

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