Wednesday, 1 October 2014
Compact disc (CD) is a digital optical disc data storage format. The format was originally developed to store and play only sound recordings (CD-DA), but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, 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 in); they are sometimes used for CD singles, storing up to 24 minutes of audio or delivering device drivers.
At the time of the technology's introduction, it had much greater capacity than computer hard drives common at the time. The reverse is now true, with hard drives far exceeding the capacity of CDs. The Compact Disc is an evolution of LaserDisc technology. Prototypes were developed by Philips and Sony independently from the mid-to-late 1970s. The two companies then collaborated to produce a standard format and related player technology which was made commercially available in 1982.
American inventor James T. Russell has been credited with inventing the first system to record digital information on an optical transparent foil which is lighted from behind by a high-power halogen lamp. Russell's patent application was first filed in 1966 and he was granted a patent in 1970. Read more...