The ability to compress data before it is written to the hard disk without any noticeable loss in speed compared to non-compressed data. Modern operating systems provide a real-time compression capability for a portion or all of the hard disk, and earlier products such as Stacker and SuperStor were third-party software that added this capability.
Images May Also Be Compressed
GIF images are compressed when they are saved, without any loss of data. JPEG images are also compressed, but eliminate pixels in the process (see lossy compression