An optical disc is a flat, usually disc-shaped object that stores information in the form of physical variations on its surface that can be read with the aid of a beam of light. Optical discs can be reflective, where the light source and detector are on the same side of the disc, or transmissive, where light shines through the disc to be detected on the other side. They may contain analog or digital information,. Design and technologyThe encoding material sits atop a thicker substrate (usually ) that makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering th. The first recorded historical use of an optical disc was in 1884 when, and recorded sound on a glass disc using a beam of light. Optophoni. There are numerous formats of optical devices on the market, all of which are based on using a laser to change the of the medium in order to duplicate the effects of the pits an.
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