Compressed files use algorithms to reduce storage space and are commonly used for archiving infrequently used files. Zip programs like WinZip and PKzip can compress and uncompress files, and some compressed files may be executable and contain viruses. Different compression formats exist, and any program that handles zip files can be used for both tasks.
A compressed document or program is a file that has been compressed by applying an algorithm to reduce the number of characters needed to store it. These algorithms are included in zip programs such as WinZip, PKzip, Power Archiver and others. When you unzip a document, the zip program reverses the algorithm to return the file to its original state. This is referred to as file recovery.
To uncompress a document means to expand it. A compressed file might only take up 523 kilobytes, but the same uncompressed file might be three or four times as large. Zipped files are equivalent to a kind of shorthand, where the encoding for repeating characters is used. However, a file is not usable in its compressed state. A document or program must be uncompressed before it can be used. Zip programs do both.
Because compressed files take up less space on your hard drive, zip programs are a popular way to archive files that are infrequently used. One can also add several files to a single zipped archive. When the archive is unpacked, the separate files are reconstituted.
In the past, when many programs ran in DOS, PKZIP was the standard zip program. To zip or unzip a document, you had to enter a command line prompt. Today’s zip programs integrate into operating systems such as Microsoft Windows and attach themselves to zipped files.
With built-in association, unzipping a document or program is as simple as double-clicking it. Zipping a file is almost as easy. Just right-click the file from Desktop Explorer to bring up a menu. One of the menu choices should be to compress the file or add it to a compressed archive. Your choices may vary depending on how you configure your zip program.
Technically, compressed files end with the .zip extension, but there are several compression formats that are often referred to generically as “compressed files,” even if they use a different format. Some of the other archive formats use .rar, .cab, .iso and .tar extensions.
Some compressed files are made executable, which means they end with the .exe extension. When you unzip such a document, the file will run a program. Malicious programmers often send executables as spam. Viruses can be spread this way, even if the program appears harmless to the recipient. A cartoon may be playing in the foreground, while another program is busy installing a virus in the background.
There are several zip programs available and some are free. You don’t need to use the same zip program to unzip a document that you used to zip it. Any program that handles zip files will work for both tasks.
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