A compact disc or CD is a form of digital media. It is an optical device which can be encoded with digital data. When you examine a CD you can tell it is mainly plastic. In fact, a CD is almost pure polycarbonate plastic. There is a spiral track molded into the top of the plastic. The surface of a CD is reflective because the disc is coated with a thin layer of aluminum or sometimes gold.
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Keywords: CD, elements, plastic