CD ‘compact disk’ is a digital optical disk data storage format. The format was originally developed to store and play back sound recordings only (CD-DA), but was later adapted for storage of date (CD-Rom). Serval other formats were further delivered from these, including write-once audios and data storage. (CD-R), rewritable media (CD-RW), video compact disk (VCD), super video compact disk (SUCD), photo CD, Picture CD, CD and enhanced music CD. Audio CDs and audio CD players have been commercially available since October 1982.
standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to about 80 minutes of uncompressed audio or 700 MiB (actually about 703 MiB or 737 MB) of data. The mini CD has various diameters ranging from 60 to 80 millimetres (2.4 to 3.1 inch) they are sometimes used for CD singles, Storing up to 24 minutes of audio or delivering device drivers.
At the time of the technologies introduction it had much greater capacity then a computers hard drive common at the time. The reverse is now true, with hard drives far acceding the capacity of CD’s.
In 2004, worldwide sales of CD audio, CR-ROM reached about 30 billion discs. By 2007 200 billion CDs had been sold worldwide. Compact discs are increasingly being replaced or supplemented by other forms of digital distortion and storage, such as downloading and flash drives. With audio CD sales dropping nearly 50% from their peak in 2000.
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