CD stands for Compact Disc. The CD is an optical disc format developed by Philips and Sony starting in 1979. It was originally developed as a format to store audio and still is the biggest selling medium for recorded music from major and independent record companies. An audio CD can hold up to 80 minutes of audio data, stored using 16-bit PCM at a sampling rate of 44100hz. A standard CD is approximately 120mm in diameter, but 80mm discs also exist that can store about 20 minutes of audio.
Later on, the CD format became widely used for data storage too. CD-ROM allowed software companies worldwide to distribute their software and games on CDs. In 2004, the annual worldwide sales of audio CDs, CD-ROM and rewriteable CDs reached about 30 billion discs, emphasizing the extreme success of the format, which is expected to remain widely used for many years even with the DVD format now an affordable solution also.
Recordable CD Media
In the 90s, recordable CD media showed up and has since become a huge success worldwide. Using recordable CD formats, which come mainly in 640MB and 700MB capacities, consumers can use easy software solutions like Nero to burn their very own audio CDs or create compilations of data CDs. They can also be used to create the inexpensive MPEG-1-based VideoCD and MPEG-2-based Super VideoCD formats, which are supported by a very large amount of stand-alone DVD players.
Since recordable media can easily be used in copying retail audio CDs, some countries enforce a levy fee on top of the retail price of recordable CD (and DVD) media. The levies vary by country but their aim is to compensate copyright holders for when recordable CDs, CD-Rs, are used to copy retail music CDs. While some consumer advocates cite fair use rights to combat the levies, the record industry itself has avoided recognizing the issue of fair use, at least in the case of the major record companies.
CD-R and CD-RW (erasable, re-writable) media is particularly inexpensive, but also can be very unreliable if "cheap" media is purchased too often.