Compact disc

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The read side of a compact disc

Compact Disc (CD) is an optical disc that is used to store data. These are actually made to replace floppy disks that were used to store files and programs from the computer. The CDs eventually caused the floppy disks to become obsolete. CDs were invented by Philips and Sony independently, but they did collaborate to create a standard format and related player technology (CD player) in 1982. CDs can hold up to 700 MB worth of data, which is about 80 minutes of audio. Mini CDs have also been crated that can store about 24 minutes of audio or program drivers.      

Later, compact discs were made that could be used to store computer files 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). They are especially popular in Asia. In Indonesia they are used instead of the more expensive DVD. The quality of a VCD is about the same as a VHS tape.

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 sound or 650-700 megabytes of data. CDs can be manufactured to hold up to 99 minutes of audio, or slightly under a gigabyte of data, by making the tracks smaller. Discs with more than 74 minutes or 650 MB are non-standard, and some CD players are not able to play them.

Some CDs are smaller; they are 80mm in diameter. They can store about 30% of a normal disc, and were intended to be used for music "singles". Mass-manufacturing made it more convenient to use a full-size CD and leave most of it empty. This greatly limited the appeal and sale of 80mm CDs.

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