James T. Russell invented the CD (compact disc) in the 1960s as a storage medium in which light, rather than physical contact between the disc and the player, was used to store and retrieve information. In the 1980s, CDs became the primary format for storing music or computer information.
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CDs begin with a glass layer coated with photoresist, a type of polymeric coating that changes properties when it is exposed to light. As the disc spins, a Laser Beam Recorder (LBR) marks rivets in the photoresist. When the photoresist is developed, the marks made by the laser form tiny pits or stripes down to the surface of the glass. The photoresist is coated with a nickel alloy to make a mould, which is called the father.
The father is used to stamp an image of the CD data onto a layer of polycarbonate. This process is called electroforming. Polycarbonate is a type of hard plastic that gives CDs their strength and versatility. Its name comes from the carbonate groups that make up its main structure. It is heat resistant to 125 degrees Celsius (125 degrees Celsius) and nearly unbreakable.
The top of the polycarbonate is coated with a thin layer of aluminium. When you place a CD in a CD player, the CD spins as a laser, located beneath the CD, reads the disc. The laser beam passes through the clear polycarbonate to find the pits on the surface, and the aluminium reflects the laser light back. A layer of lacquer protects the CD's data from damage and provides a smooth surface for printing a label.
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