The Compact Disc was invented by Sony and Philips in 1981 in order to serve as a high-quality compact audio storage device which allowed for direct access to digital sound tracks. It was officially launched in October 1982. In 1984, the Compact Disc's specifications were extended (with the publication of the Yellow Book) so that it could store digital data.
CD geometry
A CD (Compact Disc) is an optical disc 12cm in diameter and 1.2mm thick (its thickness may vary from 1.1 to 1.5 mm) for storing digital information: up to 650 MB of computer data (equivalent to 300,000 typed pages) or 74 minutes of audio data. A circular hole 15mm in diameter is used to centre it on the CD player's surface.
The makeup of a CD
A CD is built from a plastic (polycarbonate) substrate and a fine, reflective metallic film (24-carat gold or a silver alloy). The reflective layer is then covered with an anti-UV acrylic finish, creating a protective surface for data. Finally, an additional layer may be added so that data can be written on the other side of the CD as well.
