A Compact Disc, or CD, is an optical disc used to store digital data although it was originally developed to store sound recordings exclusively. Audio CDs have been available commercially since October 1982 and were popular until around 2010 when other digital forms took over.
The standard CD can hold up to 80 minutes of uncompressed audio. There are also Mini CDs that hold up to 24 minutes of audio. Eventually the technology was expanded to include CD-ROM, CD-R, CD-RW, video compact discs, as well as other varieties of storage. Including all these formats, the CD had sold 200 billion units worldwide by 2007.
The audio disc was first shown publicly in 1976 by Sony. In ’78 they demonstrated an audio disc with a 150 minute play time that was very similar to the compact disc that came out later in 1982. In 1979 Sony and Philips set up a task force of engineers to design a new digital audio disc. A year later they had developed the Red Book, the standard Compact Disc standard. Philips did most of the manufacturing and modulation which provides long playing time and resilience against disc defects and scratches. Sony contributed the error-correction method, CIRC.
Polydor Pressing Operations pressed the first test CD which contained a recording of Richard Strauss’s Eine Alpensinfonie. The BBC produced the first public demonstration by playing The Bee Gees’ album Living Eyes. The first full CD to be manufactured was ABBA’s Visitors. However, Billy Joel’s 52nd Street was the first to be released alongside Sony’s CDP-101. In 1983 CD Players and discs were released in the US and this is often referred to as the “Big Bang” of the digital audio revolution. The CD was received very well by consumers and was even more popular as CD prices dropped. David Bowie was the first artist to convert his whole catalogue, 15 studio albums and four greatest hits albums, to CD.
The CD has outgrown its original purpose of replacing the gramophone has grown to become more than that including a data storage medium. In the 1985 the CD-ROM was released and in 1990 the CD-Recordable was introduced. The CD quickly replaced the audio cassette in automobile. The advent of the MP3 has dropped the sales of CDs very quickly since 2000.
The data on CDs is stored in indentations known as “pits”. A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The changes in the pits and lands result in difference in the intensity of the light and by measuring the change in the intensity the data can be read from the disc. CDs can be damaged through normal use or environmental exposure.
The data on a CD begins at the center of the disc which allows adaptation to the different size formats available. Sony and Philips aimed for a playing time of 60 minutes until it was later lengthened to 80 minutes. The increase in playing time also required an increase the size of the CD to 120 mm. The playing time was often used to gain an advantage over LPs in the early years when they were competing.
The hydraulic press is used to mass-produce replicated CDs. Once they are manufactured the CDs are polywrapped and sold in stores. The recordable CD-Rs are sold on spirals. After a CD-R is recorded it is meant to be permanent; however, the dye used to record can change over time eventually causing errors.