File Compression Basics

Suppose you wanted to send balloons from a neighborhood party shop to a friend of yours living in another state.  You would not ship them fully inflated through the mail.  Instead, to save space and shipping costs, you would deflate the balloons, and send them and instruct someone on the other end to inflate them.  This simple concept also applies to sending files across the Internet.  File compression allows you to take computer files and squeeze their contents so that the files takes up less space on a disk.

If you're downloading a file from a Web site, you will save time by downloading a compressed file, since there will be less information to transfer.  If you pay for your online connection by the hour, downloading compressed files can also save you money.

It is usually pretty easy to tell if a file has been compressed...just take a look at the file extension (the suffix end of the file) which usually consists of a period followed by three letters.

"Zipped" files are one of the most common types of compressed files.  These files have a ".ZIP" suffix at the end of the filename.  There are a number of Windows based program utilities that will compress and expand zipped files.  Three of the most common are PKZIP, a product of PKWARE Inc., and Winzip, which is published by Nico Mak Computing Inc., and our favorite The Unzip Wizard from PC Shareware, Inc..

File compression is like a kind of computer shorthand.  When you attempt to compress a file, the compression software that is being used looks for a series of repeating characters or bits in the file.  The software then replaces these blocks of repeated characters with symbols or shorter words or phrases, which are called "tokens."

For example, it takes less space for a computer file to be structured:

"10101000110101[insert 73 zeroes here]11011010010"

than this...

"1010100011010100000000000000000000000000000000000
000000000000000000000000000000000000011011010010"

When you apply a decompression program to a compressed file, the software reads the file and replaces the tokens with the original data, inflating the file back to its original size.

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