The compact disc (CD) is a molded plastic disc containing digital data that is scanned by a laser beam for the reproduction of recorded sound and other information.
A standard CD is 120 mm (4.75 inch) in diameter and 1.2 mm (0.05 inch) thick. It is composed of a clear polycarbonate plastic substrate, a reflective metallic layer, and a clear protective coating of acrylic plastic. The reflective metallic layer is where audio data is read in the form of minuscule (as short as 0.83 micrometre) depressions (pits) and contrasting flat regions (lands) that are arranged in a spiral track (groove) winding from the disc’s inner hole to its outer edge. The centres of adjacent grooves are spaced 1.6 micrometres (0.0016 mm) apart.
CD data is represented as tiny indentations known as pits, encoded in a spiral track moulded into the top of the polycarbonate layer. The areas between pits are known as lands. Each pit is approximately 100 nm deep by 500 nm wide, and varies from 850 nm to 3.5 µm in length. The distance between the tracks (the pitch) is 1.6 µm.
Since its commercial introduction in 1982, the audio CD has almost completely replaced the phonograph disc (or record) for high-fidelity recorded music.
In 1976 Phillips and Sony developed the compact discOffsite Link (CD), an optical disc used to store and playback digital data. It was originally developed to store and playback sound recordings exclusively.
Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called “Philips Introduce Compact Disc” in Eindhoven, The NetherlandsOffsite Link on March 8, 1979.
The standard for the compact disc was first proposed by Philips (Netherlands) and Sony (Japan) in 1980, and agreed upon in 1981 by the Compact Disc Standard Digital Audio Disc Committee. The first CDs became available to the public in Europe and Japan in the autumn of 1982, and the USA in 1983, where 800,000 discs were sold in the first year alone. Optical discs, which are written and read with a laser, have become the standard medium for home entertainment and computing.
The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities and its handling quality received particular praise. As the price of players sank rapidly, the CD began to gain popularity in the larger popular and rock music markets.
The CD was originally thought of as an evolution of the gramophone record, rather than primarily as a data storage medium. Only later did the concept of an “audio file” arise, and the generalizing of this to any data file. From its origins as a music format, Compact Disc has grown to encompass other applications. In June 1985, the CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also developed by Sony and Philips.
Sony launched its CDP-101 – the first commercialized CD player in 1982. Sony and Philips paid royalties from CD player sales to Battelle and Optical Recording Corporation. Time-Warner and other disc manufacturers settled with the Optical Recording Corporation in 1992, paying $30 million for patent infringement.
By the mid-1990s, however, developments in computer technology advanced such that CD recording and replication could avoid the need for a digital tape master. High-quality sound recordings could be sent from the microphone or other device directly to computer programs whose digital files could be stored on the computer’s hard disk (or magnetic storage media) before being transferred to a CD.
In 1999, just as millennials and the internet itself were coming of age, Napster hit the web and changed the world forever. Allowing a network of global users to easily share music files, the site boomed as the Recording Industry Association of America (RIAA) and other major industry organizations scrambled to catch up (and fetch their high-dollar lawyers). At its height, Napster hosted around 80 million users, and paved the way for other peer-to-peer sites like LimeWire, uTorrent, and many more. While Napster was eventually shuttered in 2001, the genie was out of the bottle, so to speak, and the piles of cash that CD sales had hauled in began to slowly but surely fade away.
The Visitors, an album by Abba, a Swedish pop group, was the first-ever created compact disc.
The Eagles 1976 album is the most sold CD ever, with over 38 million copies sold.
The compact disc (CD) remains the most popular format for listening to music, with a global sales revenue of over $17 billion (then £8.6 billion) in 2005. This is a drop of 6% on the previous year – the fastest growing format, unsurprisingly, is digital, which saw an increase in sales revenue of 188% between 2004 and 2005.
In March 2006, a 170 CD ($119 or £61) set of the complete works of Mozart was awarded a gold record in France for sales of over 100,000 in three months.
The largest display of compact discs consists of 489,440 and was achieved by Byeong Sam Jeon, Sung Hun Lee, Ho Il Kim and public volunteers (all South Korea), during the 2015 Cheongju International Craft Biennale, in Cheongju, South Korea, on 16 September 2015.