View source for Compact disc

{{short description|Digital optical disc data storage format}}
{{Redirect2|CD|CDs|other uses|CD (disambiguation)|and|CDS (disambiguation)}}
{{For|the 'audio CD' specifically|Compact Disc Digital Audio}}
{{Use dmy dates|date=January 2023}}
{{Use American English|date=March 2021}}
{{Infobox storage medium
| title = Compact disc
| name = Compact disc
| logo = [[File:Compact Disc wordmark.svg|frameless|upright=0.6|class=skin-invert]]
| image = CD autolev crop new.jpg
| caption = The readable surface of a compact disc is [[iridescent]] because it includes a spiral track wound tightly enough to cause light to [[diffraction grating|diffract]] into a full [[visible spectrum]].
| type = [[Optical disc]]
| capacity = {{Unbulleted indent list
  | 650{{nbndash}}870&nbsp;[[MiB]] data
  | 74{{nbndash}}99 minutes audio
  }}
| read = 780&nbsp;nm [[laser diode]]
| write = 780&nbsp;nm laser diode
| released = {{Unbulleted list
  | [[Japan|JP]]: {{start date|1982|10|df=yes}}
  | [[North America|NA]]/[[Europe|EU]]: {{start date |1983|3|df=yes}}<ref>{{cite web |url=https://historyofinformation.com/detail.php?entryid=1189#:~:text=Visitors%20by%20ABBA-,.,United%20States%20and%20other%20markets. |title=The Compact Disc (CD) is Developed |website=historyofinformation.com |access-date=9 February 2023}}</ref>
  }}
| standard = [[Rainbow Books]]
| owner = [[Philips]]{{,}}[[Sony]]
| dimensions = {{Unbulleted indent list
  | [[Diameter]]: {{Cvt|120|mm}}
  | Thickness: {{Cvt|1.2|mm}}
  }}
| use = {{Unbulleted indent list
  | [[Audio storage]]
  | [[Computer data storage]]
  }}
| extended from = [[LaserDisc]]
| extended to = {{hlist
  | [[CD-RW]]
  | [[DVD]]
  | {{nowrap|[[Super Audio CD]]}}
  }}
}}
{{Optical disc authoring}}

The '''compact disc''' ('''CD''') is a [[Digital media|digital]] [[optical disc]] [[data storage]] format co-developed by [[Philips]] and [[Sony]] to store and play [[digital audio]] recordings. It employs the [[Compact Disc Digital Audio]] (CD-DA) standard and is capable of holding of uncompressed [[stereo]] audio. First released in [[Japan]] in October 1982, the CD was the second optical disc format to reach the market, following the larger [[LaserDisc]] (LD). In later years, the technology was adapted for computer data storage as [[CD-ROM]] and subsequently expanded into various writable and multimedia formats. {{As of|2007}}, over 200 billion CDs (including audio CDs, CD-ROMs, and [[CD-R]]s) had been sold worldwide.

Standard CDs have a diameter of {{convert|120|mm|abbr=off}} and typically hold up to 74 minutes of audio or approximately {{bytes|650|Mi|link=mebibyte}} of data. This was later regularly extended to 80 minutes or {{bytes|700|Mi}} by reducing the spacing between data tracks, with some discs unofficially reaching up to 99 minutes or {{bytes|870|Mi}} which falls outside established specifications. Smaller variants, such as the [[Mini CD]], range from {{convert|60|to|80|mm}} in diameter and have been used for [[CD single]]s or distributing [[device driver]]s and software.

The CD gained widespread popularity in the late 1980s and early 1990s. By 1991, it had surpassed the [[phonograph record]] and the [[compact cassette|cassette tape]] in sales in the [[United States]], becoming the dominant physical audio format. By 2000, CDs accounted for 92.3% of the U.S. music market share.<ref>{{Cite web |title=U.S. Music Revenue Database |url=https://www.riaa.com/u-s-sales-database/ |access-date=2024-03-17 |website=RIAA}}</ref> The CD is widely regarded as the final dominant format of the [[album era]], before the rise of [[MP3]], [[Music download|digital downloads]], and [[Music streaming service|streaming platforms]] in the mid-2000s led to its decline.<ref>{{Cite news |last=Lynskey |first=Dorian |date=2015-05-28 |title=How the compact disc lost its shine |url=https://www.theguardian.com/music/2015/may/28/how-the-compact-disc-lost-its-shine |access-date=2024-03-17 |work=The Guardian}}</ref>

Beyond audio playback, the compact disc was adapted for general-purpose data storage under the [[CD-ROM]] format, which initially offered more capacity than contemporary personal computer [[hard disk drive]]s. Additional derived formats include write-once discs ([[CD-R]]), rewritable media ([[CD-RW]]), and multimedia applications such as [[Video CD]] (VCD), [[Super Video CD]] (SVCD), [[Photo CD]], [[Picture CD]], [[CD-i|Compact Disc Interactive]] (CD-i), [[Enhanced Music CD]], and [[Super Audio CD]] (SACD), the latter of which can include a standard CD-DA layer for [[backward compatibility]].

== History ==
{{Excerpt|Compact Disc Digital Audio|History|subsections=yes}}

== Physical details ==
{{More citations needed section|date=May 2016|talk=Numbers in the Physical Details section}}
{{see also|Shaped compact disc}}
[[File:CD layers.svg|thumb|Diagram of CD layers {{ordered list |list_style_type=upper-alpha
 |1=<!--A-->A polycarbonate disc layer has the data encoded by using bumps.
 |2=<!--B-->A shiny layer reflects the laser.
 |3=<!--C-->A layer of lacquer protects the shiny layer.
 |4=<!--D-->Artwork is [[Screen printing|screen printed]] on the top of the disc.
 |5=<!--E-->A laser beam is reflected off the CD to a sensor, which converts it into electronic data.
}}|alt=]]

A CD is made from {{convert|1.2|mm|adj=on}} thick, [[polycarbonate]] plastic, and weighs 14–33 grams.<ref>{{Cite book|last=Pohlmann|first=Ken C.|url=https://books.google.com/books?id=GkIaGZ0HWcMC&q=compact+disc+weight&pg=PA303|title=The Compact Disc: A Handbook of Theory and Use|date=1989|publisher=A-R Editions, Inc.|isbn=978-0-89579-228-0|language=en}}</ref> From the center outward, components are: the center spindle hole (15&nbsp;mm), the first-transition area (clamping ring), the clamping area (stacking ring), the second-transition area (mirror band), the program (data) area, and the rim. The inner program area occupies a radius from 25 to 58&nbsp;mm.

A thin layer of [[aluminum]] or, more rarely, [[Gold compact disc|gold]] is applied to the surface, making it reflective. The metal is protected by a film of lacquer normally [[spin coated]] directly on the reflective layer. The label is printed on the lacquer layer, usually by [[screen printing]] or [[offset printing]].

[[File:Compactdiscar.jpg|thumb|left|''Pits'' and ''lands'' of a compact disc under a [[microscope]] ]]CD data is represented as tiny indentations known as ''pits'', encoded in a spiral track molded into the top of the polycarbonate layer. The areas between pits are known as ''lands''. Each pit is approximately 100&nbsp;[[Nanometre|nm]] deep by 500&nbsp;nm wide, and varies from 850&nbsp;nm to 3.5&nbsp;[[μm]] in length.<ref>{{cite web |url=http://www.laesieworks.com/digicom/Storage_CD.html |title=Compact Disc|access-date=6 May 2016 |url-status=live |archive-url=https://web.archive.org/web/20160512100137/http://www.laesieworks.com/digicom/Storage_CD.html |archive-date=12 May 2016}}</ref> The distance between the windings (the ''pitch'') is 1.6&nbsp;μm (measured center-to-center, not between the edges).<ref>{{cite web |url=http://www.multimediadirector.com/help/technology/downloads/tech_docs/cdintroduction.pdf |title=Introduction to CD and CD-ROM |last=Sharpless |first=Graham |date=July 2003 |publisher=Deluxe Global Media Services Ltd|access-date=3 May 2016 |url-status=live |archive-url=https://web.archive.org/web/20160309135812/http://www.multimediadirector.com/help/technology/downloads/tech_docs/cdintroduction.pdf |archive-date=9 March 2016}}</ref><ref name="IEC908">{{cite web |url=https://webstore.iec.ch/publication/3885 |title=IEC 60908 Audio recording - Compact disc digital audio system |url-status=live |archive-url=https://web.archive.org/web/20160506194944/https://webstore.iec.ch/publication/3885 |archive-date=6 May 2016}}</ref><ref name="IEC10149">{{cite web |url=https://webstore.iec.ch/publication/9362 |title=ISO/IEC 10149 Information technology -- Data interchange on read-only 120 mm optical data disks (CD-ROM) |url-status=live |archive-url=https://web.archive.org/web/20160506194949/https://webstore.iec.ch/publication/9362 |archive-date=6 May 2016}}</ref>

[[File: Compact disk data layer 2d 3d.PNG|thumb|right|Individual pits are visible on the micrometer scale.]]

When playing an audio CD, a motor within the CD player spins the disc to a scanning velocity of 1.2–1.4&nbsp;m/s ([[constant linear velocity]], CLV)—equivalent to approximately 500 RPM at the inside of the disc, and approximately 200 RPM at the outside edge.<ref name=":0">{{Cite web |date=2024-03-07 |title=Compact disc (CD) {{!}} Definition & Facts {{!}} Britannica |url=https://www.britannica.com/technology/compact-disc |access-date=2024-03-24 |website=www.britannica.com |language=en}}</ref> The track on the CD begins at the inside and spirals outward so a disc played from beginning to end slows its rotation rate during playback.

[[File:Comparison CD DVD HDDVD BD.svg|thumb|upright=1.35|left|Comparison of various optical storage media<!-- parameters: track pitch (p), pit width (w) and minimum length (l), and laser spot size (⌀) and wavelength (λ). -->]]
The program area is 86.05&nbsp;cm<sup>2</sup> and the length of the recordable spiral is {{no wrap|86.05&nbsp;cm<sup>2</sup> / 1.6 μm {{=}}}} {{no wrap|5.38&nbsp;km.}} With a scanning speed of 1.2&nbsp;m/s, the playing time is 74 minutes or 650&nbsp;MiB of data on a CD-ROM. A disc with data packed slightly more densely is tolerated by most players (though some old ones fail). Using a linear velocity of 1.2&nbsp;m/s and a narrower track pitch of 1.5&nbsp;μm increases the playing time to 80 minutes, and data capacity to 700&nbsp;MiB. Even denser tracks are possible, with semi-standard 90 minute/800&nbsp;MiB discs having 1.33&nbsp;μm, and 99 minute/870&nbsp;MiB having 1.26&nbsp;μm,<ref>{{cite conference |title=Optical measurements upon compact discs in education in optoelectronics |book-title=Electronics Technology (ISSE), 2010 33rd International Spring Seminar on Electronics Technology |last1=Pencheva |first1=Tamara |last2=Gyoch |first2=Berkant |last3=Mashkov |first3=Petko |date=2010-05-01 |pages=531–535 |isbn=978-1-4244-7849-1 |url=https://www.researchgate.net/figure/for-CD-R-74-min-are-obtained-as-follows_tbl1_261263539 }}</ref> but compatibility suffers as density increases.

[[File: CD Pits at 6.25x Magnification.jpg|alt=This is a photomicrograph of the pits at the inner edge of a CD-ROM; 2-second exposure under visible fluorescent light.|thumb|The pits in a CD are 500 [[nanometre|nm]] wide, between 830 nm and 3,000 nm long and 150 nm deep.]]

A CD is read by focusing a 780&nbsp;nm [[wavelength]] ([[near infrared]]) [[semiconductor laser]] (early players used [[Helium–neon laser|He{{nbndash}}Ne laser]]<ref>{{Cite book | url=https://books.google.com/books?id=Ad5G1HWtDRgC&q=cd+player+hene&pg=PA824 |title = Springer Handbook of Lasers and Optics|isbn = 9783642194092|last1 = Träger|first1 = Frank|date = 5 May 2012| publisher=Springer }}</ref>) through the bottom of the polycarbonate layer. The change in height between pits and lands results in a difference in the way the light is reflected. Because the pits are indented into the top layer of the disc and are read through the transparent polycarbonate base, the pits form bumps when read.<ref>An Introduction to Digital Audio, John Watkinson, 1994</ref> The laser hits the disc, casting a circle of light wider than the modulated spiral track reflecting partially from the lands and partially from the top of any bumps where they are present. As the laser passes over a pit (bump), its height means that the round trip path of the light reflected from its peak is 1/2 wavelength out of phase with the light reflected from the land around it. This is because the height of a bump is around 1/4 of the wavelength of the light used, so the light falls 1/4 out of phase before reflection and another 1/4 wavelength out of phase after reflection. This causes partial [[Wave interference|cancellation]] of the laser's reflection from the surface. By measuring the reflected intensity change with a [[photodiode]], a modulated signal is read back from the disc.<ref name=":0" />

To accommodate the spiral pattern of data, the laser is placed on a mobile mechanism within the disc tray of any CD player. This mechanism typically takes the form of a sled that moves along a rail. The sled can be driven by a [[worm gear]] or [[linear motor]]. Where a worm gear is used, a second shorter-throw linear motor, in the form of a coil and magnet, makes fine position adjustments to track eccentricities in the disk at high speed. Some CD drives (particularly those manufactured by Philips during the 1980s and early 1990s) use a swing arm similar to that seen on a gramophone.

[[File:CDM210 cd laufwerk.jpg|thumb|Philips CDM210 CD Drive]]

The pits and lands do ''not'' directly represent the 0s and 1s of [[binary data]]. Instead, [[non-return-to-zero, inverted]] encoding is used: a change from either pit to land or land to pit indicates a 1, while no change indicates a series of 0s. There must be at least two, and no more than ten 0s between each 1, which is defined by the length of the pit. This, in turn, is decoded by reversing the [[eight-to-fourteen modulation]] used in mastering the disc, and then reversing the [[cross-interleaved Reed–Solomon coding]], finally revealing the raw data stored on the disc. These encoding techniques (defined in the ''[[Compact Disc Digital Audio#Data encoding|Red Book]]'') were originally designed for [[CD Digital Audio]], but they later became a standard for almost all CD formats (such as [[CD-ROM]]).

=== Integrity ===
CDs are susceptible to damage during handling and from environmental exposure. Pits are much closer to the label side of a disc, enabling defects and contaminants on the clear side to be out of focus during playback. Consequently, CDs are more likely to suffer damage on the label side of the disc. Scratches on the clear side can be repaired by refilling them with similar refractive plastic or by careful polishing. The edges of CDs are sometimes incompletely sealed, allowing gases and liquids to enter the CD and corrode the metal reflective layer and/or interfere with the focus of the laser on the pits, a condition known as [[disc rot]].<ref name="clir">Council on Library and Information Resources: [https://www.clir.org/pubs/reports/pub121/sec5.html Conditions that Affect CDs and DVDs] {{webarchive|url=https://web.archive.org/web/20160915012213/https://www.clir.org/pubs/reports/pub121/sec5.html |date=15 September 2016 }}</ref> The fungus ''[[Geotrichum candidum]]'' has been found—under conditions of high heat and humidity—to consume the polycarbonate plastic and aluminium found in CDs.<ref>{{Cite journal|url=http://www.nature.com/news/1998/010628/full/news010628-11.html|title=Fungus eats CD|year=2001|journal=Nature|doi=10.1038/news010628-11|url-status=live|archive-url=https://web.archive.org/web/20131212044729/http://www.nature.com/news/1998/010628/full/news010628-11.html|archive-date=12 December 2013|last1=Bosch|first1=Xavier |issn=0028-0836|url-access=subscription}}</ref><ref>{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/1402533.stm|title=Fungus 'eats' CDs|date=June 2001|publisher=BBC|url-status=live|archive-url=https://web.archive.org/web/20131212220948/http://news.bbc.co.uk/2/hi/science/nature/1402533.stm|archive-date=12 December 2013}}</ref>

The [[data integrity]] of compact discs can be measured using [[Optical Disc#Surface error scanning|surface error scanning]], which can measure the rates of different types of data errors, known as ''C1'', ''[[C2 error|C2]]'', ''CU'' and extended (finer-grain) error measurements known as ''E11'', ''E12'', ''E21'', ''E22'', ''E31'' and ''E32'', of which higher rates indicate a possibly damaged or unclean data surface, low media quality, [[disc rot|deteriorating media]] and [[CD-R|recordable media]] written to by a malfunctioning [[CD writer]].

Error scanning can reliably predict data losses caused by media deterioration. Support of error scanning differs between vendors and models of [[Optical disc drive#Appliances|optical disc drive]]s<!-- TSSTcorp and LiteON support it according to forum screenshots, but we need a better source. -->, and ''extended'' error scanning (known as ''"advanced error scanning"'' in [[Nero DiscSpeed]]) which reports the six aforementioned E-type errors has only been available on [[Plextor#Optical drives|Plextor]] and some [[BenQ]] optical drives so far, as of 2020.<ref name=gleitz>{{cite web|language=de|url=https://gleitz.info/forum/index.php?thread/32049-philips-dvd-r-8x-infodiscr20/&postID=308650#post308650|date=2006-11-18|title=Philips DVD-R 8x (InfodiscR20) - Philips - Gleitz}}</ref><ref name=qpx-g>{{cite web |title=QPxTool glossary |url=https://qpxtool.sourceforge.io/glossar.html |website=qpxtool.sourceforge.io |publisher=QPxTool |access-date=22 July 2020 |date=2008-08-01 |ref=QPx-Glossary}}</ref>

=== Disc shapes and diameters ===
[[File:Comparison disk storage.svg|thumb|upright=1.35|Comparison of several forms of disk storage showing tracks (not to scale); green denotes start and red denotes end.<br/><nowiki>*</nowiki> Some CD-R(W) and DVD-R(W)/DVD+R(W) recorders operate in ZCLV, CAA or CAV modes.]]

The digital data on a CD begins at the inside near the spindle hole and spirals outward toward the edge in a single track. The outward spiral allows adaptation to different-sized discs. Standard CDs are available in two sizes. By far, the most common is {{convert|120|mm}} in diameter, with a 74-, 80, 90, or 99-minute audio capacity and a 650, 700, 800, or 870&nbsp;MiB (737,280,000-byte) data capacity. Discs are {{convert|1.2|mm}} thick, with a {{convert|15|mm}} center hole. The size of the hole was chosen by Joop Sinjou and based on a Dutch 10-cent coin: a [[dubbeltje]].<ref>{{Cite web|title=Perfecting the Compact Disc System - The six Philips/Sony meetings - 1979-1980 |url=https://dutchaudioclassics.nl/The-six-meetings-Philips-Sony-1979-1980-The-Start-of-Digital-Audio/|access-date=2022-01-26|website=DutchAudioClassics.nl }}</ref> Philips/Sony patented the physical dimensions.<ref>{{Cite web |date=2015-06-25 |title=Response To Koninklijke Philips Electronics, N.V.'s, Sony Corporation of Japan's And Pioneer Electronic Corporation of Japan's Request For Business Review Letter |url=https://www.justice.gov/atr/response-koninklijke-philips-electronics-nvs-sony-corporation-japans-and-pioneer-electronic |access-date=2022-05-14 |website=justice.gov |language=en}}</ref>

The official Philips history says the capacity was specified by Sony executive [[Norio Ohga]] to be able to contain the entirety of [[Beethoven's Ninth Symphony]] on one disc.<ref name="Ohgaobituary"/> 
According to Philips chief engineer [[Kees Immink]], this is a myth,<ref name="Imminknature">{{Cite journal|journal=Nature Electronics|volume=1|date=2018|title=How we made the compact disc
|author=K.A. Schouhamer Immink|author-link=Kees Schouhamer Immink
|url=https://www.researchgate.net/publication/324571504|access-date=2018-04-16
}}</ref> as the [[Eight-to-fourteen modulation|EFM]] code format had not yet been decided in December 1979, when the 120&nbsp;mm size was adopted. The adoption of EFM in June 1980 allowed 30 percent more playing time that would have resulted in 97 minutes for 120&nbsp;mm diameter or 74 minutes for a disc as small as {{convert|100|mm}}. Instead, the information density was lowered by 30 percent to keep the playing time at 74 minutes.<ref name="Immink2"/><ref>Tim Buthe and Walter Mattli, The New Global Rulers: The Privatization of Regulation in the World Economy, Princeton University Press, Feb. 2011.</ref> The 120&nbsp;mm diameter has been adopted by subsequent formats, including [[Super Audio CD]], [[DVD]], [[HD DVD]], and [[Blu-ray]] Disc. The {{convert|80|mm|adj=on}} diameter discs ("[[Mini CD]]s") can hold up to 24 minutes of music or 210&nbsp;MiB.

{| class="wikitable"
|-
! Physical size
! Audio capacity
! CD-ROM data capacity
! Definition
|-
| 120&nbsp;mm || 74–80 min || 650–700&nbsp;[[Megabyte|MB]] || Standard size
|-
| 80&nbsp;mm || 21–24 min || 185–210&nbsp;MB || Mini-CD size
|-
| 80×54&nbsp;mm&nbsp;– 80×64&nbsp;mm || ~6 min || 10–65&nbsp;MB || [[Business card]] size
|}

===SHM-CD===
[[File:SHM-CD_Subline_logo.svg|thumb|Logo used for SHM-CDs]]
'''SHM-CD''' (short for ''Super High Material Compact Disc'') is a variant of the Compact Disc, which replaces the [[polycarbonate]] base with a proprietary material. This material was created during joint research by [[Universal Music Japan]] and [[JVC]] into manufacturing high-clarity [[Liquid-crystal display|liquid-crystal displays]].

SHM-CDs are fully compatible with all CD players since the difference in light refraction is not detected as an error. JVC claims that the greater fluidity and clarity of the material used for SHM-CDs results in a higher reading accuracy and improved sound quality.<ref>{{Cite web |last=CDJapan |title=All About SHM-CD Format |url=https://www.cdjapan.co.jp/feature/shmcd_allabout |access-date=2024-02-22 |website=CDJapan |language=en}}</ref> However, since the CD-Audio format contains inherent [[Compact Disc Digital Audio#Data encoding|error correction]], it is unclear whether a reduction in read errors would be great enough to produce an improved output.

== Logical format ==
{{Unreferenced section|date=May 2018}}
=== Audio CD ===
[[File:CDP101a.jpg|thumb|[[Sony CDP-101]] from 1982, the first commercially released [[CD]] player for [[consumer]]s]]
[[File:CD player.jpg|thumb|Philips CD100 from 1983, the first commercially released CD player in the US and Europe]]
{{Main|Compact Disc Digital Audio}}
The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in a document produced in 1980 by the format's joint creators, Sony and Philips.<ref>{{Cite web|title=IEC 60908:1999 {{!}} IEC Webstore|url=https://webstore.iec.ch/publication/3885|access-date=2020-07-09|website=webstore.iec.ch|archive-url=https://web.archive.org/web/20160506194944/https://webstore.iec.ch/publication/3885|archive-date=6 May 2016|url-status=live}}</ref> The document is known colloquially as the ''Red Book'' [[CD-DA]] after the color of its cover. The format is a two-channel 16-bit [[PCM]] encoding at a [[44.1 kHz|44.1&nbsp;kHz]] [[sampling rate]] per channel. [[Four-channel Compact Disc Digital Audio|Four-channel sound]] was to be an allowable option within the ''Red Book'' format, but has never been implemented. [[Monaural]] audio has no existing standard on a ''Red Book'' CD; thus, the mono source material is usually presented as two identical channels in a standard ''Red Book'' stereo track (i.e., [[mono sound#Mirrored mono|mirrored mono]]); an [[MP3 CD]], can have audio file formats with mono sound.

[[CD-Text]] is an extension of the ''Red Book'' specification for an audio CD that allows for the storage of additional text information (e.g., album name, song name, artist) on a standards-compliant audio CD. The information is stored either in the [[Optical disc authoring|lead-in area]] of the CD, where there are roughly five kilobytes of space available or in the [[subcode]] channels R to W on the disc, which can store about 31 megabytes.

[[Compact Disc + Graphics]] is a special audio compact disc that contains graphics data in addition to the audio data on the disc. The disc can be played on a regular audio CD player, but when played on a special CD+G player, it can output a graphics signal (typically, the CD+G player is hooked up to a television set or a computer monitor); these graphics are almost exclusively used to display lyrics on a television set for [[karaoke]] performers to sing along with. The CD+G format takes advantage of the channels R through W. These six bits store the graphics information.

[[CD + Extended Graphics]] (CD+EG, also known as CD+XG) is an improved variant of the [[#CD + Graphics|Compact Disc + Graphics]] (CD+G) format. Like CD+G, CD+EG uses basic CD-ROM features to display text and video information in addition to the music being played. This extra data is stored in subcode channels R-W. Very few CD+EG discs have been published.

=== Super Audio CD ===
{{Main|Super Audio CD}}
Super Audio CD (SACD) is a high-resolution, read-only [[optical disc|optical]] [[audio storage|audio disc]] format that was designed to provide [[high fidelity|higher-fidelity]] digital audio reproduction than the ''Red Book''. Introduced in 1999, it was developed by Sony and Philips, the same companies that created the ''Red Book''. SACD was in a [[format war]] with [[DVD-Audio]], but neither has replaced audio CDs. The SACD standard is referred to as the ''Scarlet Book'' standard.

Titles in the SACD format can be issued as hybrid discs; these discs contain the SACD audio stream as well as a standard audio CD layer which is playable in standard CD players, thus making them backward compatible.

=== CD-MIDI ===
CD-[[MIDI]] is a format used to store music-performance data, which upon playback is performed by electronic instruments that synthesize the audio. Hence, unlike the original ''Red Book'' CD-DA, these recordings are not digitally sampled audio recordings. The CD-MIDI format is defined as an extension of the original ''Red Book''.

=== CD-ROM ===
{{Main|CD-ROM}}
For the first few years of its existence, the CD was a medium used purely for audio. In 1988, the ''Yellow Book'' [[CD-ROM]] standard was established by Sony and Philips, which defined a non-volatile optical data [[computer data storage]] medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive.

=== Video CD ===
{{Main|Video CD}}
Video CD (VCD, View CD, and Compact Disc digital video) is a standard digital format for storing video media on a CD. VCDs are playable in dedicated VCD players, most modern [[DVD-Video]] players, personal computers, and some video game consoles. The VCD standard was created in 1993 by Sony, Philips, [[Panasonic|Matsushita]], and [[JVC]] and is referred to as the ''White Book'' standard.

Overall picture quality is intended to be comparable to [[VHS]] video. Poorly compressed VCD video can sometimes be of lower quality than VHS video, but VCD exhibits block artifacts rather than analog noise and does not deteriorate further with each use. 352×240 (or [[Source Input Format|SIF]]) resolution was chosen because it is half the vertical and half the horizontal resolution of the NTSC video. 352×288 is a similarly one-quarter PAL/SECAM resolution. This approximates the (overall) resolution of an analog VHS tape, which, although it has double the number of (vertical) scan lines, has a much lower horizontal resolution.

=== Super Video CD ===
{{Main|Super Video CD}}
Super Video CD (Super Video Compact Disc or SVCD) is a format used for storing video media on standard compact discs. SVCD was intended as a successor to VCD and an alternative to DVD-Video and falls somewhere between both in terms of technical capability and picture quality.

SVCD has two-thirds the [[display resolution|resolution]] of DVD, and over 2.7 times the resolution of VCD. One CD-R disc can hold up to 60 minutes of standard-quality SVCD-format video. While no specific limit on SVCD video length is mandated by the specification, one must lower the video bit rate, and therefore quality, to accommodate very long videos. It is usually difficult to fit much more than 100 minutes of video onto one SVCD without incurring a significant quality loss, and many hardware players are unable to play a video with an instantaneous bit rate lower than 300 to 600 [[kilobit]]s per second.

=== Photo CD ===
{{Main|Photo CD}}
Photo CD is a system designed by [[Kodak]] for digitizing and storing photos on a CD. Launched in 1992, the discs were designed to hold nearly 100 high-quality images, scanned prints, and slides using special proprietary encoding. Photo CDs are defined in the ''Beige Book'' and conform to the [[CD-ROM XA]] and CD-i Bridge specifications as well. They are intended to play on CD-i players, Photo CD players, and any computer with suitable software (irrespective of [[operating system]]). The images can also be printed out on photographic paper with a special Kodak machine. This format is not to be confused with Kodak [[Picture CD]], which is a consumer product in CD-ROM format.

=== CD-i ===
{{Main|Philips CD-i}}
The Philips ''[[Green Book (CD standard)|Green Book]]'' specifies a standard for interactive multimedia compact discs designed for [[CD-i]] players (1993). CD-i discs can contain audio tracks that can be played on regular [[CD player]]s, but CD-i discs are not compatible with most [[CD-ROM]] drives and software. The [[CD-i Ready]] specification was later created to improve compatibility with audio CD players, and the [[CD-i Bridge]] specification was added to create CD-i-compatible discs that can be accessed by regular CD-ROM drives.

=== CD-i Ready ===
{{Main|CD-i Ready}}
Philips defined a format similar to CD-i called [[CD-i Ready]], which puts CD-i software and data into the [[Pregap#Computer data in pregap|pregap]] of track 1. This format was supposed to be more compatible with older audio CD players.

=== Enhanced Music CD (CD+) ===
{{Main|Blue Book (CD standard)}}
Enhanced Music CD, also known as CD Extra or CD Plus, is a format that combines [[CD-DA|audio tracks]] and [[CD-ROM|data tracks]] on the same disc by putting audio tracks in a first [[Session (CD)|session]] and data in a second session. It was developed by Philips and Sony, and it is defined in the ''[[Blue Book (CD standard)|Blue Book]]''.

=== VinylDisc ===
{{Main|VinylDisc}}
VinylDisc is the hybrid of a standard audio CD and the [[Gramophone record|vinyl record]]. The vinyl layer on the disc's label side can hold approximately three minutes of music.

== Manufacture, cost, and pricing ==
{{Main|Compact Disc manufacturing}}
In 1995, material costs were 30 cents for the jewel case and 10 to 15 cents for the CD. The wholesale cost of CDs was $0.75 to $1.15, while the typical retail price of a prerecorded music CD was $16.98.<ref name="cd costs">{{cite news |author=Neil Strauss |date=5 July 1995 |url=https://www.nytimes.com/1995/07/05/arts/pennies-that-add-up-to-16.98-why-cd-s-cost-so-much.html?pagewanted=all&src=pm |title=Pennies That Add Up to $16.98: Why CD's Cost So Much – New York Times |work=[[The New York Times]] |access-date=25 July 2013 |url-status=live |archive-url=https://web.archive.org/web/20130811000713/http://www.nytimes.com/1995/07/05/arts/pennies-that-add-up-to-16.98-why-cd-s-cost-so-much.html?pagewanted=all&src=pm |archive-date=11 August 2013 }}</ref> On average, the store received 35 percent of the retail price, the record company 27 percent, the artist 16 percent, the manufacturer 13 percent, and the distributor 9 percent.<ref name="cd costs"/> When [[8-track cartridges]], [[compact cassette]]s, and CDs were introduced, each was marketed at a higher price than the format they succeeded, even though the cost to produce the media was reduced. This was done because the perceived value increased. This continued from [[phonograph record]]s to CDs, but was broken when [[Apple Inc.|Apple]] marketed MP3s for $0.99, and albums for $9.99. The incremental cost, though, to produce an MP3 is negligible.<ref>{{cite news |first=Amy |last=Harmon |url=https://www.nytimes.com/2003/10/12/arts/music-what-price-music.html?pagewanted=all&src=pm |title=MUSIC; What Price Music? |work=[[The New York Times]] |date=12 October 2003 |access-date=25 July 2013 |url-status=live |archive-url=https://web.archive.org/web/20130512175059/http://www.nytimes.com/2003/10/12/arts/music-what-price-music.html?pagewanted=all&src=pm |archive-date=12 May 2013 }}</ref>

== Writable compact discs ==

=== Recordable CD ===
[[File:Maxell CD-R 700MB 40x 20040321.jpg|thumb|700&nbsp;[[MiB]] CD-R next to a [[mechanical pencil]] for scale]]
{{Main|CD-R}}
Recordable Compact Discs, [[CD-R]]s, are injection-molded with a blank data spiral. A photosensitive dye is then applied, after which the discs are metalized and lacquer-coated. The write laser of the [[CD recorder]] changes the color of the dye to allow the read laser of a standard [[CD player]] to see the data, just as it would with a standard stamped disc. The resulting discs can be read by most CD-ROM drives and played in most audio CD players. CD-Rs follow the ''Orange Book'' standard.

CD-R recordings are designed to be permanent. Over time, the dye's physical characteristics may change causing read errors and data loss until the reading device cannot recover with error correction methods. Errors can be predicted using [[Optical disc#Surface error scanning|surface error scanning]]. The design life is from 20 to 100 years, depending on the quality of the discs, the quality of the writing drive, and storage conditions.<ref>{{cite web|title=Cost Per Gigabyte of Popular Data Storage - Infographic|url=https://www.blankmediaprinting.com/blog-article/cost-gigabyte-popular-data-storage-types-infographic/|work=Blank Media Printing|access-date=1 January 2016|archive-url=https://web.archive.org/web/20160417144636/https://www.blankmediaprinting.com/blog-article/cost-gigabyte-popular-data-storage-types-infographic|archive-date=17 April 2016|url-status=live}}</ref> Testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions.<ref name="AutoMR-14"/><ref name="AutoMR-15"/> This failure is known as [[disc rot]], for which there are several, mostly environmental, reasons.<ref>{{Cite web|url=https://www.clir.org/pubs/reports/pub121/sec5.html|title=5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources|website=clir.org|access-date=2016-07-05|url-status=live|archive-url=https://web.archive.org/web/20160915012213/https://www.clir.org/pubs/reports/pub121/sec5.html|archive-date=15 September 2016}}</ref>

The recordable audio CD is designed to be used in a consumer audio CD recorder. These consumer audio CD recorders use SCMS ([[Serial Copy Management System]]), an early form of [[digital rights management]] (DRM), to conform to the AHRA ([[Audio Home Recording Act]]). The Recordable Audio CD is typically somewhat more expensive than CD-R due to lower production volume and a 3 percent [[Audio Home Recording Act#AHRA royalties|AHRA royalty]] used to compensate the music industry for the making of a copy.<ref name="McFadden"/>

High-capacity recordable CD is a higher-density recording format that can hold 20% more data than conventional discs.<ref>{{cite web |url=http://www.osta.org/technology/cdqa7.htm |title=Understanding CD-R & CD-RW |publisher=Osta.org |access-date=25 July 2013 |url-status=live |archive-url=https://web.archive.org/web/20130801123221/http://www.osta.org/technology/cdqa7.htm |archive-date=1 August 2013 }}</ref> The higher capacity is incompatible with some recorders and recording software.<ref name="cdrfaq">{{cite web
 |url         = http://www.cdrfaq.org/faq03.html
 |title       = CD-Recordable FAQ – Section 3
 |date        = 9 January 2010
 |access-date = 25 November 2013
 |quote       = Small quantities of 90-minute and 99-minute blanks have appeared [...] Indications are that many recorders and some software don't work with the longer discs.
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20131118040105/http://www.cdrfaq.org/faq03.html
 |archive-date = 18 November 2013
}}</ref>

=== ReWritable CD ===
{{Main|CD-RW}}
[[CD-RW]] is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser, in this case, is used to heat and alter the properties (amorphous vs. crystalline) of the alloy, and hence change its reflectivity. A CD-RW does not have as great a difference in reflectivity as a pressed CD or a CD-R, and so many earlier CD audio players cannot read CD-RW discs, although most later CD audio players and stand-alone [[DVD]] players can. CD-RWs follow the ''Orange Book'' standard.

The ReWritable Audio CD is designed to be used in a consumer audio CD recorder, which will not (without modification) accept standard CD-RW discs. These consumer audio CD recorders use the [[Serial Copy Management System]] (SCMS), an early form of [[digital rights management]] (DRM), to conform to the United States' [[Audio Home Recording Act]] (AHRA). The ReWritable Audio CD is typically somewhat more expensive than CD-R due to (a) lower volume and (b) a 3 percent [[Audio Home Recording Act#AHRA royalties|AHRA royalty]] used to compensate the music industry for the making of a copy.<ref name="McFadden"/>

== Copy protection ==
{{Main|Compact Disc and DVD copy protection}}
{{see also|Sony BMG copy protection rootkit scandal}}
The ''Red Book'' audio specification, except for a simple ''anti-copy'' statement in the subcode, does not include any [[copy protection]] mechanism. Known at least as early as 2001,<ref name="BadCDs"/> attempts were made by record companies to market ''copy-protected'' non-standard compact discs, which cannot be [[Ripping|ripped]], or copied, to hard drives or easily converted to other formats (like [[FLAC]], [[MP3]] or [[Vorbis]]). One major drawback to these copy-protected discs is that most will not play on either computer CD-ROM drives or some standalone CD players that use CD-ROM mechanisms. Philips has stated that such discs are not permitted to bear the trademarked ''Compact Disc Digital Audio'' logo because they violate the ''Red Book'' specifications. Numerous copy-protection systems have been countered by readily available, often free, software, or even by simply turning off automatic [[AutoPlay]] to prevent the running of the DRM [[executable]] program.

== See also ==
* [[Comparison of popular optical data-storage systems]]
* [[Optical disc packaging]]
* [[Extended Resolution Compact Disc]]
* {{annotated link|High Definition Compatible Digital}}
* {{annotated link|Compact disc bronzing}}
* {{annotated link|DualDisc}}
* {{annotated link|Hidden track}}
* {{annotated link|SPARS code}}
* [[List of optical disc manufacturers]]

== References ==
{{reflist|refs=

<ref name="Ohgaobituary">{{cite news
| url          = https://www.foxnews.com/tech/sony-chairman-credited-with-developing-cds-dies
| title        = Sony chairman credited with developing CDs dies
| access-date  = 2 August 2024
| work         = Fox News
| date         = 24 April 2011
| url-status   = live
| archive-url  = https://web.archive.org/web/20130521044524/http://www.foxnews.com/world/2011/04/24/sony-chairman-credited-developing-cds-dies/
| archive-date = 21 May 2013
}}</ref>

<ref name="Immink2">{{Cite journal 
| journal     = IEEE Information Theory Society Newsletter
| volume      = 57 
| date        = 2007
| title       = Shannon, Beethoven, and the Compact Disc
| author      = K. Schouhamer Immink 
| author-link = Kees Schouhamer Immink 
| url         = https://www.researchgate.net/publication/322951358
| pages       = 42–46
| access-date = 2018-02-06
}}</ref>

<ref name="Immink">{{Cite journal
| journal      = Journal of the Audio Engineering Society
| volume       = 46
| issue        = 5
| date         = 1998
| title        = The Compact Disc Story
| author       = K. Schouhamer Immink
| author-link  = Kees Schouhamer Immink
| url          = https://www.aes.org/e-lib/browse.cfm?elib=12144
| pages        = 458–460
| access-date  = 6 February 2018
| archive-date = 19 April 2023
| archive-url  = https://web.archive.org/web/20230419210311/https://www.aes.org/e-lib/browse.cfm?elib=12144
| url-status   = live
}}</ref>

<ref name="Compact Disc Digital Audio Immink">{{Cite journal
| journal      = Journal of the Audio Engineering Society
| volume       = 46
| issue        = 5
| date         = 1998
| title        = The Compact Disc Story
| author       = K. Schouhamer Immink
| author-link  = Kees Schouhamer Immink
| url          = https://www.aes.org/e-lib/browse.cfm?elib=12144
| pages        = 458–460
| access-date  = 6 February 2018
| archive-date = 19 April 2023
| archive-url  = https://web.archive.org/web/20230419210311/https://www.aes.org/e-lib/browse.cfm?elib=12144
| url-status   = live
}}</ref>

<ref name="AutoMR-14">{{cite web
| url          = http://www.cdfreaks.com/news/CD-Recordable-discs-unreadable-in-less-than-two-years.html
| title        = CD-R Unreadable in Less Than Two Years
| publisher    = cdfreaks.com
| access-date  = 1 February 2007
| url-status   = dead
| archive-url  = https://web.archive.org/web/20070214195603/http://www.cdfreaks.com/news/CD-Recordable-discs-unreadable-in-less-than-two-years.html
| archive-date = 14 February 2007
}}</ref>

<ref name="AutoMR-15">{{cite web
| url          = http://www.pc-active.nl/toonArtikel.asp?artikelID=508
| archive-url  = https://web.archive.org/web/20050204065340/http://www.pc-active.nl/toonArtikel.asp?artikelID=508
| archive-date = 4 February 2005
| title        = CD-R ROT
| access-date  = 1 February 2007
}}</ref>

<ref name="McFadden">{{cite web
| url          = http://www.cdrfaq.org/
| title        = CD-Recordable FAQ
| author       = Andy McFadden
| date         = 8 August 2007
| access-date  = 20 September 2007
| url-status   = live
| archive-url  = https://web.archive.org/web/20070920211018/http://www.cdrfaq.org/
| archive-date = 20 September 2007
}}</ref>

<ref name="BadCDs">{{cite web
| url          = http://uk.eurorights.org/issues/cd/bad/
| archive-url  = https://web.archive.org/web/20011205101807/http://uk.eurorights.org/issues/cd/bad/
| archive-date = 5 December 2001
| title        = Copy Protected CDs
| author       = Campaign For Digital Rights
| date         = 5 December 2001
}}</ref>

<ref name="SonyHistorical">{{cite journal
| url          = http://www.aes.org/e-lib/browse.cfm?elib=2912
| url-access   = subscription
| title        = A Long Play Digital Audio Disc System
| date         = March 1979
| website      = Audio Engineering Society
| access-date  = 14 February 2009
| url-status   = live
| archive-url  = https://web.archive.org/web/20090725223113/http://www.aes.org/e-lib/browse.cfm?elib=2912
| archive-date = 25 July 2009
}}</ref>

<ref name="peek">{{cite journal
| first   = Hans B.
| last    = Peek
| title   = The Emergence of the Compact Disc
| journal = IEEE Communications Magazine
| date    = January 2010
| pages   = 10–17
| volume  = 48
| number  = 1
| issn    = 0163-6804
| doi     = 10.1109/MCOM.2010.5394021
| s2cid   = 21402165
}}</ref>

<ref name="BBC6950933">{{cite news
| url          = http://news.bbc.co.uk/2/hi/technology/6950933.stm
| title        = How the CD Was Developed
| work         = BBC News
| date         = 17 August 2007
| access-date  = 17 August 2007
| archive-url  = https://web.archive.org/web/20071222035025/http://news.bbc.co.uk/2/hi/technology/6950933.stm
| archive-date = 22 December 2007
}}</ref>

}}<!-- end of reflist -->

== Further reading ==
* [[Ecma International]]. [https://ecma-international.org/publications-and-standards/standards/ecma-130/ ''Standard ECMA-130: Data Interchange on Read-only 120&nbsp;mm Optical Data Disks (CD-ROM)''], 2nd edition (June 1996).
* Pohlmann, Kenneth C. (1992). [https://archive.org/details/compactdischandb0000pohl ''The Compact Disc Handbook'']. Middleton, Wisconsin: A-R Editions. {{ISBN|0-89579-300-8}}.
* Peek, Hans et al. (2009) [https://www.springer.com/engineering/electronics/book/978-1-4020-9552-8 ''Origins and Successors of the Compact Disc'']. Springer Science+Business Media B.V. {{ISBN|978-1-4020-9552-8}}.
* Peek, Hans B., [https://www.philips.com/c-dam/corporate/research/technologies/cd/The-Emergence-of-the-Compact-Disc_v2.pdf ''The emergence of the compact disc''], IEEE Communications Magazine, Jan. 2010, pp.&nbsp;10–17.
* [[Heitaro Nakajima|Nakajima, Heitaro]]; Ogawa, Hiroshi (1992) [https://books.google.com/books?id=9G9Nu9n0DJQC ''Compact Disc Technology''], Tokyo, Ohmsha Ltd. {{ISBN|4-274-03347-3}}.
* Barry, Robert (2020). ''Compact Disc (Object Lessons)''. New York: Bloomsbury. {{ISBN|978-1-5013-4851-8}}.

== Notes ==
{{notelist}}

== External links ==
{{Commons and category|Compact disc|Compact discs}}
* [https://www.youtube.com/watch?v=ut_40U0t9pU Video] How Compact Discs are Manufactured
* [http://www.cdrfaq.org/ CD-Recordable FAQ] Exhaustive basics on CD-Recordable's
* [https://archive.today/20080129201342/http://www.research.philips.com/newscenter/dossier/optrec/beethoven.html Philips history of the CD (cache)]
* [https://archive.today/20121216094847/http://www.ip.philips.com/licensing/licensingprogramshistory/history_cdplayer_joint.html Patent History (CD Player)]&nbsp;– published by [[Philips]] in 2005
* [https://archive.today/20121206014421/http://www.ip.philips.com/licensing/licensingprogramshistory/history_cddisc_joint.html Patent History CD Disc]&nbsp;– published by [[Philips]] in 2003
* [https://web.archive.org/web/20081220113637/http://www.sony.co.jp/SonyInfo/CorporateInfo/History/SonyHistory/2-08.html Sony History, Chapter 8, This is the replacement of Gramophone record ! (第8章 レコードに代わるものはこれだ)]&nbsp;– [[Sony]] website in Japanese
* [https://www.soundfountain.com/amb/cd25years.html Popularized History on Soundfountain]
* [https://fieldday.ie/40-years-of-the-compact-disc/ A Media History of the Compact Disc] (1-hour podcast interview)

{{Compact disc}}
{{Audio formats}}
{{Music technology}}
{{Sony Corp}}
{{Lasers}}
{{Authority control}}

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