Tutorials & help

Compressed files

Summary

• Abstract
• File compression : what ? why ?
• 7-Zip : short description, download link
• 7-Zip's configuration
• Compressing/uncompressing files with 7-Zip

Abstract

Compressing files is useful to save space and bandwidth. 7-Zip is a free, high-performing compression software.

File compression : what ? why ?

On the internet, the files you download are most often compressed files, eg the original files have been treated to fit in a smaller disk size.
There are two kinds of compression : lossy compression vs lossless compression :

• As its name says, the lossy compression makes the original file smaller by losing the informations that are the least useful.
  For instance, MP3 is a lossy audio compression format : to make it simple, it removes all the audio data that we can't hear, making the sound file smaller.
  JPEG is a lossy picture compression format : to make it simple, it blurs the pictures a bit to gain space, but not enough for us to realize the picture is blurred.
• The lossless compression is a compression that keeps all the original informations, so we can restore the original file. Note : there are two kinds of lossless compressions : some are general compressions, that can be used to compress any filetype, and other are special compression, that can be used to compress only one type of file, most often pictures or audio files.
  For instance, TIFF is a lossless compression for pictures. UPX is a software that can only compress executable files (exe, dll, ocx...)
  Zip is the most famous all-purpose compression format. You can use it to compress pictures, video, audio, text files... any file : you can even use it to compress a JPEG-compressed picture (but you won't save a lot of space doing so...).

In this tutorial, we'll only talk about general-purpose compression formats, and more particularly about the 7z format, which is one of the best (see our compressors test).

Compressing files enables you to save space on your hard drive, but, most of all, to download files faster.
You need to know how to use compressed files because (almost) all the files on the internet are compressed files.

7-Zip : short description, download link

7-Zip is a free file archiver with high compression ratio, distributed under the GNU LGPL. It works in Windows 98/ME/NT/2000/XP. Command line version of 7-Zip can be used in Linux via Wine program.
You can download it on 7-Zip.org.

7-Zip's configuration

Once you've installed 7-Zip, you'll probably want to change some settings.
Launch 7-Zip (Start → Programs → 7-Zip → 7-Zip File Manage) and choose Tools → Options from the menu. In the System tab, associate 7-Zip with the extensions you want : at least 7z, and some/all others depending on what programs you already have. If you have no other compression software, you might want to associate 7-Zip with all these extensions.
In the Plugins tab, select 7-Zip and click Options. In the system folder of the new window, you can edit 7-Zip's integration to the shell context menu. I advise you to check the cascaded context menu, otherwise it will add a lot of items right in the first level of the context menu. Then choose the items you want. I advise you all but the compress and mail functions, but anyway you'll see later if you want to add or remove some items.

Compressing/uncompressing files with 7-Zip

In the Windows explorer, right select the file(s) you want to compress. To select several files, hold the CTRL key while clicking on each file, or select the first file, then hold the SHIFT key and click on the last file. Then right click on your selection. In the context menu, choose 7-Zip → Add to archive (if you chose the cascaded style).
Let's use simple settings :

• Type the name of your archive or keep the suggested name.
• Then choose the archive format (you should use 7z if you want the best compression, but you should use Zip if you want a faster compression).
• Then choose the compression level. The higher the level, the better (but the slower) the compression.
• You can edit the other settings if you want to (add a password, create SFX archive = you won't need 7-Zip to be installed to uncompress the archive, wich can be useful if you want to distribute your archive to people who don't have 7-Zip, and so on).
• Near the bottom of the page, there is a create solid archive box. If you check it, your archive will be compressed better but, to modify it, you'll need to completely uncompress it then recompress it. So you won't be able to drag and drop files into it.

To uncompress a 7-Zip archive, in the Windows explorer, right-click on the archive and choose one of the extract options in 7-Zip.