Compact Disc
A Compact Disc (CD) is a type of optical disc. It is flat and round, and is used to store digital data. It is used to store music and other sounds (and sometimes called an "audio CD"). The sounds on the CD are played using a compact disc player. It was developed by Phillips and Sony.
Later, Compact Discs were made that could be used to put computer files on in the same way as audio compact discs. These are called CD-ROMs (Compact Disc Read-Only Memory). The computer 'reads' the disc using a CD-ROM drive. Another use is to store MPEG videos cheaply, these CDs are called VCDs (Video CDs) and are especially popular in Asia. For example, in Indonesia they are used instead of the more expensive DVD.
The diameter of a normal CD is 120 mm. The middle hole in a CD is about the size of a five cent coin (About 1.5 cm). The person who decided the size was Dutch and used the size of an old Dutch coin (old because the Dutch now have switched to the Euro), called a "dubbeltje", or dime. A CD usually holds a maximum of 74-80 minutes of audio or 650-700 megabytes of data.
Some CDs are smaller; they are 80mm in diameter. They can hold about 30% of the capacity of a normal disc.
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