Optical disc
In computing, sound reproduction, and video an optical disc is a flat, circular, plastic disc coated with material on which bits may be stored in the form of highly reflective areas and significantly less reflective areas, from which the stored data may be read when illuminated with a narrow-beam source, such as a laser diode.
The first optical disc was the video laserdisc created by Philips as early as in the late 1960s and marketed in the mid-1970s in cooperation with Sony. The knowledge gained from this development led to the creation of the compact disc in 1980.
The bits on an optical disc are stored sequentially on a continuous spiral track from the innermost track and outwards.
