When compact discs arrived over 20 years ago, they promised convenience, durability and superior content capacity. Although they proved convenient, fingerprints, scratches and gouges proved a real problem. To understand why, we need to understand how a disc is created and how it works.
1. Polycarbonate Plastic
Each disc starts out as a clear plastic disc. Data is stamped to the top of this layer, creating pits and gaps.
2. Reflective Foil
Next, a thin, reflective foil layer is applied to the data side of the plastic layer. This silver, copper or gold layer is what reflects the laser back to the player and allows the stamped data to be read.
Third, a very thin layer of lacquer is sprayed on the foil layer and spun at a high speed. This fragile layer seals the foil layer from oxidation and exposure to the environment.
Finally, a screen-printed layer is applied to the lacquer for marketing, identification and further protection.
DVD's are essentially the same, except they contain an additional layer of polycarbonate above the stamped data. Recordable discs differ in that they do not have pre-stamped information pits. Instead, they use a photosensitive layer that, when exposed to light, forms a 'burned' impression of a pit on to this layer.
Ok, now you know how a disc is made, but what stops it from playing?
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