A CD-ROM encyclopedia is an encyclopedia delivered as reference software on a CD-ROM disc for use on a personal computer. This was the usual way computer users accessed encyclopedic knowledge from early 1990s until the late 1990s. Later DVD discs replaced CD-ROMs and from mid-2000s internet encyclopedias became dominant and replaced disc-based software encyclopedias. Some examples of CD-ROM encyclopedia are Encarta, Grolier Multimedia Encyclopedia, and Britannica.
CD-ROM encyclopedias were usually a MacOS or Microsoft Windows (3.0, 3.1 or 95/98) application on a CD-ROM disc. The user would execute the encyclopedia's software program to see a menu that allowed him to start browsing the encyclopedia's articles, and most encyclopedias also supported a way to search the contents of the encyclopedia. The article text was usually hyperlinked and also included photographs, audio clips (for example in articles about historical speeches or musical instruments), and videoclips. In the CD-ROM age the videoclips had usually a low resolution, often 160x120 or 320x240 pixels. Such encyclopedias which made use of photos, audio and video were also called multimedia encyclopedias. However, because of the online encyclopedia, CD-ROM encyclopedias have been declared obsolete.