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[[File:CD_layers.svg|CD layers|thumb]] [[File:Compactdiscar.jpg|Compactdiscar|thumb|left]] [[File:Comparison_CD_DVD_HDDVD_BD.svg|Comparison CD DVD HDDVD BD|thumb|left]] [[File:_CD_Pits_at_6.25x_Magnification.jpg|CD Pits at 6.25x Magnification|thumb]] [[File:CDM210_cd_laufwerk.jpg|CDM210 cd laufwerk|thumb]] '''Compact Disc''' ('''CD''') is an optical disc used to store digital data. It was originally developed to store and play only sound recordings 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 CD]] ([[VCD]]), [[Super Video CD]] ([[SVCD]]), [[Photo CD]], [[PictureCD]], [[CD-i]], and [[Enhanced Music CD]]. CDs and their players were introduced in the international market by [[Philips]] and [[Sony]] in 1982.

== Development ==
The development of the CD was led by a collaboration between Philips and Sony. In 1979, Philips demonstrated a prototype of the optical digital audio disc at a press conference in Eindhoven, Netherlands. Sony, on the other hand, had been able to create a disc with a larger storage capacity. The two companies agreed to unify their efforts and standardized the format. The standard was set in 1980 and was a part of the [[Red Book]] standard.

== Physical Details ==
A standard CD has a diameter of 120 mm and can hold approximately 74 to 80 minutes of uncompressed audio or 650 to 700 MB of data. A CD is made from 1.2 mm thick, polycarbonate plastic and has a thin layer of aluminum to make it reflective. Data is stored on the disc as a series of microscopic indentations. A laser is used to read the CD, with the data being read from the inner radius to the outer edge.

== Formats and Uses ==
=== Audio CDs ===
The [[Audio CD]] ([[Red Book]] standard) contains music in a digital format that is considered high quality. It was the first format of CD to be introduced, and it revolutionized the music industry by offering clearer sound quality compared to the analog formats that were prevalent at the time.

=== CD-ROM ===
The [[CD-ROM]] (Read-Only Memory) was introduced for storing data. Unlike Audio CDs, which are used primarily for music, CD-ROMs can store any form of digital data. They are widely used for software and media distribution.

=== CD-R and CD-RW ===
[[CD-R]] (Recordable) allows users to write data once and read many times, whereas [[CD-RW]] (ReWritable) can be written and erased multiple times. These formats are used for personal data storage and multimedia projects.

=== Other Formats ===
Other CD formats include [[Video CD]] (VCD), which stores video files, and [[Super Video CD]] (SVCD), which offers improved video quality compared to VCD. [[Photo CD]], [[PictureCD]], and [[CD-i]] are formats developed for specific uses, such as storing photographs or interactive media.

== Impact and Decline ==
The introduction of the CD had a profound impact on the music and computing industries. It led to the decline of analog audio formats, such as the vinyl record and cassette tape, and became the standard for physical digital audio media. However, with the advent of digital downloads and streaming services, the use of CDs has declined significantly since the early 21st century.

== See Also ==
* [[DVD]]
* [[Blu-ray Disc]]
* [[Optical disc drive]]
* [[Digital audio]]

[[Category:Audio storage]]
[[Category:Computer storage devices]]
[[Category:Digital media]]
[[Category:1982 introductions]]

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Compact disc - Revision history

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