What is a Compact Disc?

Since 1982, consumers have had access to one of the great breakthroughs in media storage technology: a slim, round, and shiny object known as the compact disc (CD). Also known as an optical disk, the 4.724 inch (120 mm) round polycarbonate CD has largely replaced less reliable but similar formats like the cassette tape and vinyl record as a unit for digitally stored audio. Despite its size, one standard compact disc may hold up to 80 minutes of music. It remains the most preferred and popular medium for audio recordings. The CD-ROM, a later version of the same technology, holds up to 700 megabytes (MB) of data and is widely used by individuals and businesses for archiving important documents, photographs, and software.

A compact disc is a made of a combination of polycarbonate plastic and a reflective layer of aluminum, gold, or other metal. It was modeled after the Laserdisc (LD), a now-obsolete medium that resembles a vinyl record in its size and a CD in its composition. Information is “burned” onto a CD’s metallic layer with a laser, in a spiral direction from the inner part of the CD to the outer rim. This encoded data or audio may then be accessed with optical disc drives like CD players, DVD players, and DVD recorders. Due to the low manufacturing quality of many compact discs, the coated surface or label of a CD may become scratched or soiled to the extent that information becomes irretrievable; however, in most cases a compact disc may be wiped delicately with a lint-free cloth to remove any excess dirt and resolve playback issues.

Other formats of the compact disc serve many purposes. The mini CD, which is much smaller at 2.362 inches (60 mm) to 3.149 inches (80 mm), holds 24 minutes of audio and is often used by musicians for music singles. The re-writable CD (CD-RW), has the ability to store media and then be “re-written” or replaced with other data at a later date. The CD-R, A similar but non-reusable version, may have information written on the CD only once.

Another version of the compact disc is the Super Audio CD (SACD), which provides high-resolution, surround sound audio a regular audio CD cannot support. A Super Video CD (SVCD) is a lower-quality alternative to a recordable DVD and is used for recording video at a lower bit rate than the standard DVD. Though many alternatives exist, the CD-R remains the most popular version of compact disc for its ability to contain many forms of information and music.