Compact disc

An optical disc used to store music and data. Commonly abbreviated CD. Compact discs are made from a thin disc of polycarbonate and a metal layer in the middle of the disc. They are available in a range of sizes but the most commonly available by a long way is 120mm in diameter. A 120mm disc can store about 74 minutes of music or about 650 megabytes of data. The format of the disk was laid out by the Dutch electronics company Philips, who own the rights to the licensing of the `CD' logo that appears on the disk. Attempts are currently (early 2002) being made by record companies to market so called `copy-protected' compact disks. These rely on deliberate errors being introduced into the data recorded on the disk; the intent is that the error-correction in a music player will enable music to be played as normal, while computer CD-ROM drives will fail with errors (though not all current drives fail, and copying software is being adapted to cope with these damaged data tracks.) Philips have stated that such disks, which are written with deliberately degraded data on them which fails the CD specification, will not be permitted to have the CD logo on their packaging; it also seems likely that Philips' new models of CD recorders will be designed to be able to record from these `protected' disks.

Compact discs cannot be easily recorded; they are manufactured by etching a glass plate and using that plate to press metal. However there are also CD-R discs, which can be recorded by a laser beam using a CD-R writer (most often on a computer, though standalone units are also available), and can be played on (most) compact disc players.

The correctness of the spellings "disc" and "disk" is not trivial, see http://www.bartleby.com/61/16/C0521600.html

See also CDDB, CD-ROM, Red Book.

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