In computing, sound reproduction, and video, an optical disc is a flat, circular, usually polycarbonate disc where data is stored in the form of pits (or bumps) within a flat surface, usually along a single spiral groove that covers the entire recorded surface of the disc. This data is generally accessed when a special material on the disc (often aluminium) is illuminated with a laser diode. The pits distort the reflected laser light. Most optical discs, with the exception of a few such as black CD-ROMs designed for the original Sony PlayStation, have a characteristic prismatic or iridescent appearance created by the grooves in the reflective layer.
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