Computer files that have been reduced in size by a compression program. Such programs are available for all computer systems. For instance, PKZIP in DOS, tar and compress in UNIX, and Stuffit for the Macintosh.

Large files that have been reduced in capacity in order to allow them to be downloaded over the internet more speedily, either using FTP or a web browser, and which require decompression software in order to be used. Unzip is one such programme for the Mac and Winzip does the trick for the PC.

Compressing a file stores the data in a format that requires less space without erasing the information. This speeds communications because smaller files can be transmitted more quickly. For example due to their large size, graphic files are commonly compressed. Examples of compressed graphic files include JPEG and GIF. Although they retain all the original information, when compressed, graphics files can suffer a reduction of quality.