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Thank you for visiting the Computer Knowledge website. If you have visited in the past you may notice that the site is reduced in size. Because of time constraints and the fact that I’m now retired and doing other things, this reduction will continue to its ultimate end some time down the road. Thank you to all visitors for your past use of the CKnow site.

What is File Compression?

Introduction

File compression is commonly used when sending a file from one computer to another over a connection that has limited bandwidth. The compression basically makes the file smaller and, therefore, the sending of the file is faster. Of course, when compressing a file and sending it to another computer that computer has to have a program that will decompress the file so it can be returned to “normal” and used.

The next step to compressing a single file is the combining of multiple files into a single compressed archive. By performing this combination process the archive both serves to make the transmission faster for all the files and manages to keep them together for convenience.

Finally, the next step after combining multiple files into a single archive is to maintain the organization of those files once inside the archive. If, for example, multiple files need to be in multiple directories (folders) in order to correctly work on the receiving computer then one characteristic of such an archive would be to keep that directory structure intact within the archive and having the decompression program maintain the directory structure when decompressing the archive.

Why So Many Formats?

You may have noticed in files you’ve encountered, been sent, or just seen written about that there are many different compression formats; each with their own different file extension and compression algorithm. Why so many? There are a variety of reasons. One is simply that different formats were developed for different operating systems over time and these legacy formats continue on today. Another is competition; companies try to develop new and “improved” formats to get the last little bit of fat out of the compression in an attempt to become the “next standard.” The type of file compressed has some bearing on the format of the file being compressed as well; pictures and text often get better compression ratios using different compression techniques for each. And, some people just like to develop something “new” in order to leave their stamp on the industry. Plus, probably as many other reasons as there are formats :-).

How to Download and Decompress Files

• Download a file simply by clicking on its filename (or on whatever link the author has provided).
• In Internet Explorer choose the save to disk option from the download dialog. In Firefox you will also be given an option to save to disk. If you are using Netscape, it may say “No Viewer Configured for File Type…” just choose the save or save to disk option.
• It is best to save the file to a temporary directory that you’ve created just for this purpose. For example, I have a subdirectory on my hard drive named \TEMPDOWN which I use strictly for downloading and decompressing files. That way you always know where the file is and you can always move it from there to a more permanent location when you are finished with it.
• Use a decompressing utility on the downloaded file. Here you have to use some thought. If the compressed file has a folder structure inside the file you may have to let the utility create this folder structure on your hard drive. Most archives with multiple files in them will have a text file with directions. It is usually called README.TXT, INSTALL.TXT, or some other similar file. Most decompression programs have the capability of displaying the contents of the archive and extracting/viewing single files in the archive. If you see an instruction file we recommend you read it first, to determine what steps are required to actually dearchive, install and/or launch the program.
• Some programs do not require any additional installation process. In these cases, you can simply create a permanent directory for the program, and copy the files from your temporary directory to the permanent program directory.
• Once you’ve completely installed the program, and you are sure that it works properly, you can go back and delete the various installation files from your temporary subdirectory. However, you should keep a copy of the original archive file just in case you need to install it again in the future.

Compression/Decompresson Software

There are a variety of programs that compress and decompress files. Some are operating system dependent and others have versions for multiple operating systems. The major programs/formats include:

• 7-Zip (.7z file) – A popular archive format. The free 7-Zip program can also handle many other formats.
• GNU Zip (.gz file) – Used on many *NIX operating systems. Many programs support this archive type.
• LHA (.lha or .lzh file) – This is now used on multiple operating systems and is a standard on Amiga systems. Free unarchivers exist.
• RAR (.rar file) – A proprietary format second only to .zip on Windows systems. WinRAR is a popular program to use although free unarchivers exist.
• StuffIt (.sit file) – A popular archive format for the Macintosh although it can be found on other operating systems.
• Tape archive (.tar file) – Used on many *NIX operating systems. Many programs support this archive type.
• WinAce (.ace file) – A format often used for CD/DVD images. The WinACE program is not free but free dearchivers exist for older versions of the format and the commercial version has a free trial period.
• Zip (.zip file) – Probably the single most popular archive format out there. Many programs support this archive type (both free and commercial). Even Windows itself can create and dearchive .zip files