Question: What Are CDs Made Of?
A compact disc or CD is a device used to store digital data. Here is a look at the composition of a compact disc or what CDs are made of.
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. The shiny metal layer reflects the laser that is used to read or write to the device. A layer of lacquer is spin-coated onto the CD to protect the metal. A label may be screen-printed or offset-printed onto the lacquer. Data is encoded by forming pits in the spiral track of the polycarbonate (though the pits appear as ridges from the perspective of the laser). A space between pits is called a land
. A change from a pit to a land or a land to a pit is a "1" in binary data, while no-change is a "0".
Scratches Are Worse on One Side than the Other
Pits are closer to the label side of a CD, so a scratch or other damage on the label side
is more likely to result in an error than one occurring on the clear side of the disc. A scratch on the clear side of the disc often can be repaired by polishing the disc or filling the scratch with a material with a similar refractive index. You basically have a ruined disc if the scratch occurs on the label side.
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