How CD Players work

Compact discs are made from a 1.2 mm thick disc of polycarbonate plastic coated with a much thinner layer of Super Purity Aluminum (or rarely, gold, used for its data longevity, such as in some limited-edition audiophile CDs) layer which is protected by a film of lacquer. The lacquer can be printed with a label. Common printing methods for compact discs are silkscreening and offset printing. CDs are available in two sizes. By far the most common is 120 mm in diameter, with a 74-minute audio capacity and a 650-MB data (See storage capacity; this form factor has also erroneously been called "CD5" since it is 4 3/4 inches in diameter, about five inches across). Such a standard disc weighs 15 grams. 80 mm discs are also available, a format which is mainly used for audio CD singles in some regions (e.g. Japan), much like the old vinyl single. Each such "miniCD" or "Maxi CD" can hold 21 minutes of music, or 180 MB of data (this form factor has also been called "CD3", since it is about three inches across).



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