Music CDs

Compact Discs (CDs) were first introduced to the music market in 1982, co developed by Philips and Sony. Due to their affordability and availability, the technology grew fast. By the 1990s recordable CDs were widely available and by 2000 most vehicles were manufactured with CD players instead of audio tape players as it had become the leading format for recorded music. The technology was also developed further and led to the development of CD ROMs, DVDs and Blue Ray, which share the same physical attributes as the music CD.

Sizes

Music CDs are available in two sizes the standard CD measures 120mm in diameter, can hold up to 700MiB of data and provides up to 80 minutes of recorded music. Mini CDs measure 80mm in diameter can store up to 210MiB of data, equating to around 24 minutes of music.

How CDs Work

A CD has a single spiral track of data that circles from the inside of the disc to the outside. This track is tiny; a micron is one millionth of a meter and the track is 0.5 microns wide. The results is a series of bumps, or pits, on the readable surface of the CD, too small to be visible to the naked eye. The CD player reads the data that is stored in these bumps, using a laser and lens system and a tracking mechanism that follows the spiral track. The data is extracted by the laser and translated into the recorded music that we hear. A complex process but thankfully not one we need to fully understand in order to enjoy our music CDs.

Collectible

As in all things, some CDs are limited edition and harder to come by than others. These have significant collectible value. Examples include Coldplays The Safety EP with less than 500 produced and only approximately 100 making it to retail and Nirvanas UK only promotional version of Pennyroyal tea in 1994, that was withdrawn before distribution. Rare CDs can fetch upwards of $1500.

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