Compact disc

An optical disc used to store music and data. Commonly abbreviated CD. Compact discs are made from a thin disc of polycarbonate and a metal layer in the middle of the disc. They are available in a range of sizes but the most commonly available by a long way is 120mm in diameter. A 120mm disc can store about 74 minutes of music of about 650 megabytes of data.

When they were first made (when was that?) it was not possible for users to record there own music or data on the disc, but now (in 2001) it is very easy using CD writers.