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File Compression

Before transferring files on the Internet, it is important to have some understanding of file compression. To send uncompressed files over the Internet, whether to friends or family or even to a person you've never met before is, to say the least, cruel and unusual punishment.

Uncompressed files, many of which are 10 times larger than their compressed cousins, can take forever to download. In addition, the very act of downloading is a bandwidth hog, with the result that any concurrent Internet surfing will slow in consideration of your new bandwidth partner (the downloading file).

In the worst-case scenario, that uncompressed file you just finished sending your boss has now grabbed all of the remaining space in his or her e-mail account, with the result that all subsequent e-mails sent to that same address are rejected for lack of space. Remember, most Internet Service Providers (ISPs) limit POP (Post Office Protocol) e-mail account space to a paltry 5MB.

In short, if you don't compress your files before sending these over the Internet, it's probably best that you don't.

What is file compression and how does it work?
Computer applications such as Microsoft Word and Excel produce files that are redundant when saved, in that the information they contain, being the little bits and bytes that make up an electronic file, is repeated over and over. For example, a particular word, formula or other such pattern could appear in a document more than 500 times. Rather than repeating this information 500 times, a compression utility for zipping files will assign a number to this particular pattern, cataloguing it only once. The descriptive bits and bytes constituting the use of this pattern 500 times are then removed.

For the more technically inclined, the rewriting of data to reduce file sizes is generally accomplished using some variation of the LZ adaptive dictionary-based algorithm. LZ refers to Lempel and Ziv, the algorithm's creators, and dictionary refers to the method of cataloguing the various pieces of data.

How is the original document restored after removing all of these bits and bytes?
Simple. An expansion program built into ZIP programs refers to the dictionary that accompanies the compressed file, and then rebuilds the document to its original specifications based on the catalogued patterns.

For related information on this topic, see our sections on
Zipping Files, Digitizing Documents, and Resizing Images.

In summary, it's best to send only compressed files over the Internet. Doing so lets other users know that you truly understand the nature of file transfers and that — more importantly — you are considerate of their time and e-mail account limitations.