Optical disc
In computing, sound reproduction, and video, an optical disc is flat, circular, usually polycarbonate disc whereon data is stored. This data is generally accessed when a special material on the disc (often aluminum) is illuminated with a laser diode.
The first optical disc was the video laserdisc created by Philips, appearing as early as the late 1960s, but not marketed until the mid-1970s. The knowledge gained from this development led to the creation of the compact disc in 1980.
The information on an optical disc is stored sequentially on a continuous spiral track from the innermost track and outwardmost track.
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