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Compact disc
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Compact disc
The readable surface of a compact disc is iridescent because it includes a spiral track wound tightly enough to cause light to diffract into a full visible spectrum.
Media typeOptical disc
Capacity
  • 650‍–‍870 MiB data
  • 74‍–‍99 minutes audio
Read mechanism780 nm laser diode
Write mechanism780 nm laser diode
StandardRainbow Books
Developed byPhilips · Sony
Dimensions
  • Diameter: 120 mm (4.7 in)
  • Thickness: 1.2 mm (0.047 in)
Usage
Extended fromLaserDisc
Extended to
Released
  • JP: October 1982 (1982-10)
  • NA/EU: March 1983 (1983-03)[1]
Optical discs
General
Optical media types
Standards
See also

The compact disc (CD) is a 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 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-Rs) had been sold worldwide.

Standard CDs have a diameter of 120 millimetres (4.7 inches) and typically hold up to 74 minutes of audio or approximately 650 MiB (681,574,400 bytes) of data. This was later regularly extended to 80 minutes or 700 MiB (734,003,200 bytes) by reducing the spacing between data tracks, with some discs unofficially reaching up to 99 minutes or 870 MiB (912,261,120 bytes) which falls outside established specifications. Smaller variants, such as the Mini CD, range from 60 to 80 millimetres (2.4 to 3.1 in) in diameter and have been used for CD singles or distributing device drivers and software.

The CD gained widespread popularity in the late 1980s and early 1990s. By 1991, it had surpassed the phonograph record and the 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.[2] The CD is widely regarded as the final dominant format of the album era, before the rise of MP3, digital downloads, and streaming platforms in the mid-2000s led to its decline.[3]

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 drives. 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, 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

[edit]
This section is an excerpt from Compact Disc Digital Audio § History.[edit]

The optophone, first presented in 1913, was an early device that used light for both recording and playback of sound signals on a transparent photograph.[4] More than thirty years later, American inventor James T. Russell has been credited with inventing the first system to record digital media on a photosensitive plate. Russell's patent application was filed in 1966, and he was granted a patent in 1970.[5] Following litigation, Sony and Philips licensed Russell's patents for recording in 1988.[6][7] It is debatable whether Russell's concepts, patents, and prototypes instigated and in some measure influenced the compact disc's design.[8]

The compact disc is an evolution of LaserDisc technology,[9] where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Unlike the prior art by Optophonie and James Russell, the information on the disc is read from a reflective layer using a laser as a light source through a protective substrate. Prototypes were developed by Philips and Sony independently in the late 1970s.[10] Although originally dismissed by Philips Research management as a trivial pursuit,[11] the CD became the primary focus for Philips as the LaserDisc format struggled.[12]

In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. The group of experts analyzed every detail of the proposed CD system and meet every two months alternating between Eindhoven and Tokyo for discussions. Each time, the experiments conducted were discussed and the best solution was chosen from the prototypes developed by Sony and Philips. After experimentation, the group decided to adopt Sony’s error correction system, CIRC. Immink, in a few months' time, developed the recording code called eight-to-fourteen modulation (EFM). EFM increases the playing time by more than 30% compared to the code used in the Philips prototype, without causing any issues with tracking. Sony and Philips decide to include EFM in the official Philips/Sony CD standard.[11] EFM and Sony’s error correction code, CIRC are the only standard essential patents, (SEP)s, of the compact disc.

After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984.[13] By 1988, CD sales in the United States surpassed those of vinyl LPs, and, by 1992, CD sales surpassed those of prerecorded music-cassette tapes.[14][15] The success of the compact disc has been credited to the cooperation between Philips and Sony, which together agreed upon and developed compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company and allowed the CD to dominate the at-home music market unchallenged.[16]

Digital audio laser-disc prototypes

[edit]

In 1974, Lou Ottens, director of the audio division of Philips, started a small group to develop an analog optical audio disc with a diameter of 20 cm (7.9 in) and a sound quality superior to that of the vinyl record.[17] However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974. In 1977, Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips's prototype compact disc was set at 11.5 cm (4.5 in), the diagonal of an audio cassette.[9][18]

Heitaro Nakajima, who developed an early digital audio recorder within Japan's national public broadcasting organization, NHK, in 1970, became general manager of Sony's audio department in 1971. In 1973, his team developed a digital PCM adaptor that made audio recordings using a Betamax video recorder. After this, in 1974 the leap to storing digital audio on an optical disc was easily made.[19] Sony first publicly demonstrated an optical digital audio disc in September 1976. A year later, in September 1977, Sony showed the press a 30 cm (12 in) disc that could play an hour of digital audio (44,100 Hz sampling rate and 16-bit resolution) using modified frequency modulation encoding.[20]

In September 1978, Sony demonstrated an optical digital audio disc with a diameter of 30 cm (12 in) with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, and cross-interleaved Reed-Solomon coding (CIRC) error correction code—specifications similar to those later settled upon for the standard compact disc format in 1980. Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels.[21] Sony's AES technical paper was published on 1 March 1979. A week later, on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc"[22] in Eindhoven, Netherlands.[23] Sony executive Norio Ohga, later CEO and chairman of Sony, and Heitaro Nakajima were convinced of the format's commercial potential and pushed further development despite widespread skepticism.[24]

Collaboration and standardization

[edit]
Dutch inventor and Philips chief engineer Kees Schouhamer Immink was part of the team that produced the standard compact disc in 1980

In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology.[25] After a year of experimentation and discussion, the task force produced the Red Book CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996.[citation needed]

Philips coined the term compact disc in line with another audio product, the Compact Cassette,[26] and contributed the general manufacturing process, based on video LaserDisc technology. Philips also contributed eight-to-fourteen modulation (EFM), while Sony contributed the error-correction method, CIRC, which offers resilience to defects such as scratches and fingerprints.

The Compact Disc Story,[27] told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The task force consisted of around 6 persons,[11][28] though according to Philips, the compact disc was "invented collectively by a large group of people working as a team".[29]

Initial launch and adoption

[edit]

Early milestones in the launch and adoption of the format included:

  • The first test pressing was of a recording of Richard Strauss's An Alpine Symphony, recorded December 1–3, 1980 and played by the Berlin Philharmonic and conducted by Herbert von Karajan, who had been enlisted as an ambassador for the format in 1979.[30]
  • The world presentation took place during the Salzburg Easter Festival on 15 April 1981, at a press conference of Akio Morita and Norio Ohga (Sony), Joop van Tilburg (Philips), and Richard Busch (PolyGram), in the presence of Karajan who praised the new format.[31]
  • The first public demonstration was on the BBC television programme Tomorrow's World in 1981, when the Bee Gees' album Living Eyes (1981) was played.[32]
  • The first commercial compact disc was produced on 17 August 1982, a 1979 recording of Chopin waltzes performed by Claudio Arrau.[33]
  • The first 50 titles were released in Japan on 1 October 1982,[34] the first of which was a re-release of Billy Joel's 1978 album 52nd Street.[35]
  • The first CD played on BBC Radio was in October 1982.[citation needed]
  • The Japanese launch was followed on 14 March 1983 by the introduction of CD players and discs to Europe[36] and North America where CBS Records released sixteen titles.[37]

The first artist to sell a million copies on CD was Dire Straits, with their 1985 album Brothers in Arms.[38] One of the first CD markets was devoted to reissuing popular music whose commercial potential was already proven. The first major artist to have their entire catalog converted to CD was David Bowie, whose first fourteen studio albums (up to Scary Monsters (and Super Creeps)) of (then) sixteen were made available by RCA Records in February 1985, along with four greatest hits albums; his fifteenth and sixteenth albums (Let's Dance and Tonight, respectively) had already been issued on CD by EMI Records in 1983 and 1984, respectively.[39] On 26 February 1987, the first four UK albums by the Beatles were released in mono on compact disc.[40]

The growing acceptance of the CD in 1983 marked the beginning of the popular digital audio revolution.[41] It 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 gradually came down, and with the introduction of the portable Discman, the CD began to gain popularity in the larger popular and rock music markets. With the rise in CD sales, pre-recorded cassette tape sales began to decline in the late 1980s; CD sales overtook cassette sales in the early 1990s.[42][43] In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.[44]

Further development

[edit]
Sony Discman D-E307CK portable CD player with 1-bit DAC

Early CD players employed binary-weighted digital-to-analog converters (DAC), which contained individual electrical components for each bit of the DAC.[45] Even when using high-precision components, this approach was prone to decoding errors.[clarification needed][45] Another issue was jitter, a time-related defect. Confronted with the instability of DACs, manufacturers initially turned to increasing the number of bits in the DAC and using several DACs per audio channel, averaging their output.[45] This increased the cost of CD players but did not solve the core problem.

A breakthrough in the late 1980s culminated in development of the 1-bit DAC, which converts high-resolution low-frequency digital input signal into a lower-resolution high-frequency signal that is mapped to voltages and then smoothed with an analog filter. The temporary use of a lower-resolution signal simplified circuit design and improved efficiency, which is why it became dominant in CD players starting from the early 1990s. Philips used a variation of this technique called pulse-density modulation (PDM),[46] while Matsushita (now Panasonic) chose pulse-width modulation (PWM), advertising it as MASH, which is an acronym derived from their patented Multi-stAge noiSe-sHaping PWM topology.[45]

The CD was primarily planned as the successor to the vinyl record for playing music, rather than as a data storage medium. However, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Joseph Braat presented the first experiments with erasable compact discs during the 73rd AES Convention.[47] In June 1985, the computer-readable CD-ROM (read-only memory) and, in 1990, recordable CD-R discs were introduced.[a] Recordable CDs became an alternative to tape for recording and distributing music and could be duplicated without degradation in sound quality.

Other newer video formats such as DVD and Blu-ray use the same physical geometry as CD, and most DVD and Blu-ray players are backward compatible with audio CDs.

Peak

[edit]

CD sales in the United States peaked by 2000.[48] By the early 2000s, the CD player had largely replaced the audio cassette player as standard equipment in new automobiles, with 2010 being the final model year for any car in the United States to have a factory-equipped cassette player.[49]

Two new formats were marketed in the 2000s designed as successors to the CD: the Super Audio CD (SACD) and DVD-Audio. However neither of these were adopted partly due to increased relevance of digital (virtual) music and the apparent lack of audible improvements in audio quality to most human ears.[50] These effectively extended the CD's longevity in the music market.[51]

Decline

[edit]

With the advent and popularity of Internet-based distribution of files in lossy-compressed audio formats such as MP3, sales of CDs began to decline in the 2000s. For example, between 2000 and 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%.[52] Despite rapidly declining sales year-over-year, the pervasiveness of the technology lingered for a time, with companies placing CDs in pharmacies, supermarkets, and filling station convenience stores to target buyers less likely to be able to use Internet-based distribution.[12]

In 2012, CDs and DVDs made up only 34% of music sales in the United States.[53] By 2015, only 24% of music in the United States was purchased on physical media, two thirds of this consisting of CDs;[54] however, in the same year in Japan, over 80% of music was bought on CDs and other physical formats.[55] In 2018, U.S. CD sales were 52 million units—less than 6% of the peak sales volume in 2000.[48] In the UK, 32 million units were sold, almost 100 million fewer than in 2008.[56] In 2018, Best Buy announced plans to decrease their focus on CD sales, however, while continuing to sell records, sales of which are growing during the vinyl revival.[57][58][59]

During the 2010s, the increasing popularity of solid-state media and music streaming services caused automakers to remove automotive CD players in favor of minijack auxiliary inputs, wired connections to USB devices and wireless Bluetooth connections.[60] Automakers viewed CD players as using up valuable space and taking up weight which could be reallocated to more popular features, like large touchscreens.[61] By 2021, only Lexus and General Motors were still including CD players as standard equipment with certain vehicles.[61]

Current status

[edit]

CDs continued to be strong in some markets such as Japan where 132 million units were produced in 2019.[62]

The decline in CD sales has slowed in recent years; in 2021, CD sales increased in the US for the first time since 2004,[63] with Axios citing its rise to "young people who are finding they like hard copies of music in the digital age".[64] It came at the same time as both vinyl and cassette reached sales levels not seen in 30 years.[65] The RIAA reported that CD revenue made a dip in 2022, before increasing again in 2023 and overtook downloading for the first time in over a decade.[66]

In the US, 33.4 million CD albums were sold in the year 2022.[67] In France in 2023, 10.5 million CDs were sold, almost double that of vinyl, but both of them represented generated 12% each of the French music industry revenues.[68]

Awards and accolades

[edit]

Sony and Philips received praise for the development of the compact disc from professional organizations. These awards include:

  • Technical Grammy Award for Sony and Philips, 1998.[69]
  • IEEE Milestone award, 2009, for Philips alone with the citation: "On 8 March 1979, N.V. Philips' Gloeilampenfabrieken demonstrated for the international press a Compact Disc Audio Player. The demonstration showed that it is possible by using digital optical recording and playback to reproduce audio signals with superb stereo quality. This research at Philips established the technical standard for digital optical recording systems."[70]

Physical details

[edit]
See also: Shaped compact disc
Diagram of CD layers
  1. A polycarbonate disc layer has the data encoded by using bumps.
  2. A shiny layer reflects the laser.
  3. A layer of lacquer protects the shiny layer.
  4. Artwork is screen printed on the top of the disc.
  5. A laser beam is reflected off the CD to a sensor, which converts it into electronic data.

A CD is made from 1.2-millimetre (0.047 in) thick, polycarbonate plastic, and weighs 14–33 grams.[71] From the center outward, components are: the center spindle hole (15 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 mm.

A thin layer of aluminum or, more rarely, 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.

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 nm deep by 500 nm wide, and varies from 850 nm to 3.5 μm in length.[72] The distance between the windings (the pitch) is 1.6 μm (measured center-to-center, not between the edges).[73][74][75]

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 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.[76] 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.

Comparison of various optical storage media

The program area is 86.05 cm2 and the length of the recordable spiral is 86.05 cm2 / 1.6 μm = 5.38 km. With a scanning speed of 1.2 m/s, the playing time is 74 minutes or 650 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 m/s and a narrower track pitch of 1.5 μm increases the playing time to 80 minutes, and data capacity to 700 MiB. Even denser tracks are possible, with semi-standard 90 minute/800 MiB discs having 1.33 μm, and 99 minute/870 MiB having 1.26 μm,[77] but compatibility suffers as density increases.

This is a photomicrograph of the pits at the inner edge of a CD-ROM; 2-second exposure under visible fluorescent light.
The pits in a CD are 500 nm wide, between 830 nm and 3,000 nm long and 150 nm deep.

A CD is read by focusing a 780 nm wavelength (near infrared) semiconductor laser (early players used He‍–‍Ne laser[78]) 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.[79] 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 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.[76]

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.

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 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

[edit]

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.[80] The fungus Geotrichum candidum has been found—under conditions of high heat and humidity—to consume the polycarbonate plastic and aluminium found in CDs.[81][82]

The data integrity of compact discs can be measured using surface error scanning, which can measure the rates of different types of data errors, known as C1, 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, deteriorating media and 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 drives, 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 and some BenQ optical drives so far, as of 2020.[83][84]

Disc shapes and diameters

[edit]
Comparison of several forms of disk storage showing tracks (not to scale); green denotes start and red denotes end.
* 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 120 millimetres (4.7 in) in diameter, with a 74-, 80, 90, or 99-minute audio capacity and a 650, 700, 800, or 870 MiB (737,280,000-byte) data capacity. Discs are 1.2 millimetres (0.047 in) thick, with a 15 millimetres (0.59 in) center hole. The size of the hole was chosen by Joop Sinjou and based on a Dutch 10-cent coin: a dubbeltje.[85] Philips/Sony patented the physical dimensions.[86]

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.[87] According to Philips chief engineer Kees Immink, this is a myth,[88] as the EFM code format had not yet been decided in December 1979, when the 120 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 mm diameter or 74 minutes for a disc as small as 100 millimetres (3.9 in). Instead, the information density was lowered by 30 percent to keep the playing time at 74 minutes.[89][90] The 120 mm diameter has been adopted by subsequent formats, including Super Audio CD, DVD, HD DVD, and Blu-ray Disc. The 80-millimetre (3.1 in) diameter discs ("Mini CDs") can hold up to 24 minutes of music or 210 MiB.

Physical size Audio capacity CD-ROM data capacity Definition
120 mm 74–80 min 650–700 MB Standard size
80 mm 21–24 min 185–210 MB Mini-CD size
80×54 mm – 80×64 mm ~6 min 10–65 MB Business card size

SHM-CD

[edit]
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 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.[91] However, since the CD-Audio format contains inherent error correction, it is unclear whether a reduction in read errors would be great enough to produce an improved output.

Logical format

[edit]

Audio CD

[edit]
Sony CDP-101 from 1982, the first commercially released CD player for consumers
Philips CD100 from 1983, the first commercially released CD player in the US and Europe
Main article: 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.[92] 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 sampling rate per channel. 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., 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 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 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

[edit]
Main article: Super Audio CD

Super Audio CD (SACD) is a high-resolution, read-only optical audio disc format that was designed to provide 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

[edit]

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

[edit]
Main article: 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

[edit]
Main article: 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, 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 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

[edit]
Main article: 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 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 kilobits per second.

Photo CD

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Main article: 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

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Main article: Philips CD-i

The Philips 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 players, 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

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Main article: 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 of track 1. This format was supposed to be more compatible with older audio CD players.

Enhanced Music CD (CD+)

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Main article: Blue Book (CD standard)

Enhanced Music CD, also known as CD Extra or CD Plus, is a format that combines audio tracks and data tracks on the same disc by putting audio tracks in a first session and data in a second session. It was developed by Philips and Sony, and it is defined in the Blue Book.

VinylDisc

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Main article: VinylDisc

VinylDisc is the hybrid of a standard audio CD and the vinyl record. The vinyl layer on the disc's label side can hold approximately three minutes of music.

Manufacture, cost, and pricing

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Main article: 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.[93] 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.[93] When 8-track cartridges, compact cassettes, 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 records to CDs, but was broken when Apple marketed MP3s for $0.99, and albums for $9.99. The incremental cost, though, to produce an MP3 is negligible.[94]

Writable compact discs

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Recordable CD

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700 MiB CD-R next to a mechanical pencil for scale
Main article: CD-R

Recordable Compact Discs, CD-Rs, 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 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.[95] Testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions.[96][97] This failure is known as disc rot, for which there are several, mostly environmental, reasons.[98]

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 AHRA royalty used to compensate the music industry for the making of a copy.[99]

High-capacity recordable CD is a higher-density recording format that can hold 20% more data than conventional discs.[100] The higher capacity is incompatible with some recorders and recording software.[101]

ReWritable CD

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Main article: 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 AHRA royalty used to compensate the music industry for the making of a copy.[99]

Copy protection

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Main article: 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,[102] attempts were made by record companies to market copy-protected non-standard compact discs, which cannot be 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

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References

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Further reading

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Notes

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Compact disc

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from Grokipedia
The Compact Disc (CD) is a digital storage medium consisting of a 12-centimeter-diameter substrate with a thin reflective aluminum layer, on which is encoded as a spiral track of microscopic pits and lands readable by a low-powered beam to retrieve stored information such as audio, video, or computer . Developed jointly by and starting in , the CD format was finalized in through their collaborative "Red Book" standard, emphasizing high-fidelity playback with a capacity for up to 74 minutes of uninterrupted sound on a single side. The origins of the CD trace back to ' early 1970s experiments with optical video discs, evolving into a dedicated audio project by 1974, while pursued parallel advancements in techniques from its PCM audio systems. A pivotal formed in 1979, driven by mutual goals to replace analog formats like vinyl records and cassettes with a durable, dust-resistant digital alternative; prototypes were demonstrated that year, leading to commercial launches in and in October 1982, followed by the in 1983. Initial CD players, such as ' CD100 and 's CDP-101, retailed for around $900–$1,000, but prices fell rapidly, enabling widespread adoption by the mid-1980s. Technically, CDs employ (PCM) for audio digitization at a 44.1 kHz sampling rate and 16-bit resolution, combined with cross-interleaved Reed-Solomon coding (CIRC) for error correction, which uses a multilayer scheme of Reed-Solomon codes with interleaving to detect and correct random errors as well as burst errors up to about 3,500 bits or defects up to 2.5 mm in length, and (EFM) to optimize data density on the disc's 1.2-millimeter-thick surface. The laser pickup tracks the spiral at a constant linear velocity of about 1.2–1.4 meters per second, converting reflected light variations into that a player's reconstructs into audible , achieving a exceeding 90 dB for near-perfect fidelity. Beyond audio CDs (CD-DA), the format expanded to include for data storage up to 650–700 MB, for recordable media using organic dye layers, and for rewritable phase-change alloys, all maintaining with original players. The CD profoundly transformed the music industry, supplanting cassettes as the dominant format by the early and driving global to a peak of approximately 2.4 billion units annually in 2000, thanks to its skip-proof playback, compact portability, and enhanced that appealed to audiophiles and casual listeners alike. Its introduction spurred innovations in and compression, laying groundwork for later technologies like files and streaming, though physical CD sales have since declined with the rise of online platforms. Despite this, the CD remains a key archival medium, with billions produced and ongoing use in and data backup applications.

History

Origins and prototypes

The origins of the compact disc trace back to early concepts of laser-based optical recording for audio in the 1960s. In 1965, American physicist James T. Russell, working at the Battelle Memorial Institute, conceived a system to record digital audio on a photosensitive medium using a laser, aiming to create a durable, noise-free alternative to vinyl records. This involved converting analog audio signals to pulse-code modulation (PCM) digital format, optically exposing a film with a focused light spot smaller than 0.01 mm to achieve high data density exceeding 10^6 bits per square inch, and reading back the data via a scanning light detector to reconstruct the signal. Russell filed his first patent application in 1966, which was granted in 1970 as US Patent 3,501,586 for an "Analog to Digital to Optical Photographic Recording and Playback System," supporting spiral or rectangular track formats on photographic film for long-lifetime audio-visual storage. He developed initial prototypes in the early 1970s, including a 1973 video demonstration using a helium-neon laser on glass plates coated with photo-sensitive material, incorporating synchronization codes that influenced later digital disc standards. Philips and Sony later licensed Russell's patents in the early 1980s to cover aspects of digital optical recording in the CD format. In the early 1970s, Research Laboratories in , , advanced technology through prototypes building on experiments. Under technical director Lou F. Ottens, who had previously invented the compact cassette, initiated the Video Long Play (VLP) project in 1969, demonstrating a 30 cm analog -scanned disc for video and audio in 1972 that used a gas for contactless playback of programs and via . By 1974, adapted this precursor for , combining optical readout with PCM encoding to store high-fidelity sound on smaller discs, achieving initial playback of analog audio records converted to digital format by December of that year. Further experiments in 1976 shifted the Audio Long Play (ALP) prototype fully to digital PCM, led by researchers Toon van Alem and Loek Boonstra, to enhance sound quality and enable error handling, resulting in a functional "" audio disc prototype by early 1979 that demonstrated 11.5 cm diameter playback of digital music. These efforts addressed the limitations of analog s by prioritizing audio-specific digital storage on substrates read by . Sony's parallel developments in the mid-1970s focused on PCM audio encoding and disc trials to achieve superior digital sound reproduction. Building on expertise in from PCM adapters for video recorders, Sony engineers under Toshitada Doi explored s for audio, demonstrating a PCM-encoded -readable in 1976 that used a 30 cm disc for extended playback, emphasizing high-resolution 16-bit encoding at sampling rates suitable for . These trials, conducted at Sony's Research Laboratory, involved early experiments with semiconductor s to read pits on reflective surfaces, aiming to surpass analog LP fidelity while fitting consumer formats. By 1978, Sony showcased a system capable of two-and-a-half hours of playback, incorporating initial error detection to mitigate readout inaccuracies from surface imperfections. Key technical challenges in these prototypes centered on reliable amid imperfections like dust, scratches, and manufacturing defects, necessitating innovations in error correction and reading mechanisms. Early systems struggled with precise focusing and tracking on spinning discs, as variations in pit depth and spacing could disrupt the servo controls that maintained the beam's 1-2 micron spot size on the 0.5 micron-wide tracks; Philips and overcame this by developing astigmatism-based focusing and three-beam tracking to ensure stable reflection detection from pits (low reflection) and lands (high reflection). For error correction, introduced the Cross-Interleaved Reed-Solomon Code (CIRC) in late 1970s prototypes, a multilayer scheme that interleaved parity symbols across data blocks to correct burst errors up to 3,500 bits and detect larger ones, enabling playback resilience equivalent to 2,000 skips per disc without audible artifacts. These solutions, rooted in mid-1970s trials, balanced data density with robustness, paving the way for standardized discs.

Standardization and early development

In 1979, Philips and Sony initiated a collaborative effort to standardize the compact disc (CD) format, drawing on Philips' expertise in video disc manufacturing and Sony's advancements in digital audio encoding. Philips, with its focus on optical video storage, proposed adapting laser disc technology for audio applications, while Sony emphasized high-fidelity digital audio derived from pulse-code modulation (PCM) systems used in professional recording. This partnership resolved early disputes over format priorities—Philips advocating for a versatile medium capable of video extensions, and Sony prioritizing audio purity—ultimately agreeing to develop an audio-focused standard first, with potential for future multimedia adaptations. The collaboration culminated in the formation of the "Red Book" standard in 1980, a comprehensive specification document jointly published by Philips and Sony that defined the Compact Disc Digital Audio (CD-DA) system. This standard specified a playing time of 74 to 80 minutes per disc to accommodate full-length classical recordings, such as Beethoven's Ninth Symphony, and adopted a 44.1 kHz sampling rate with 16-bit linear quantization for high-quality stereo audio. Key technical decisions included a spiral track pitch of 1.6 μm to optimize data density while ensuring reliable laser tracking, pit dimensions approximately 125 nm deep, 500 nm wide, and varying from 850 nm to 3.5 μm in length to encode binary data via reflective variations, and Eight-to-Fourteen Modulation (EFM) for channel encoding to minimize errors from disc imperfections. These choices balanced Philips' manufacturing efficiencies with Sony's audio performance requirements, following six intensive meetings between August 1979 and June 1980 that reconciled differences in error correction (adopting Sony's Cross-Interleaved Reed-Solomon Code, or CIRC) and modulation schemes. Internal prototypes tested these specifications, building on Philips' 1978 "Pinkeltje" player and Sony's earlier audio demonstrators, with iterative refinements to achieve stable playback. A pivotal public demonstration occurred on April 15, 1981, at a press conference in , , organized by conductor , where a 74-minute played a complete recording of Beethoven's Ninth Symphony to showcase the format's fidelity and duration capabilities. This event, attended by journalists and industry figures, validated the Red Book's viability and paved the way for commercial production.

Commercial launch and adoption

The commercial launch of the compact disc began in on October 1, 1982, with Billy Joel's album 52nd Street as the first title released, marking the debut of in format based on the Philips-Sony Red Book standard. The , the inaugural , accompanied this release at a list price of approximately 168,000 yen (equivalent to about $730 USD at the time), positioning it as a premium product for audiophiles. Discs themselves were priced around $20–$25 each, reflecting the novelty and limited production scale. The format expanded to and on March 14, 1983, with initial availability limited to high-end electronics stores and a catalog of 16 titles from CBS Records, primarily classical and . Early adoption was driven by the CD's superior —offering digital fidelity without the surface noise or degradation of vinyl records and cassette tapes—along with its durability against scratches and dust, and the convenience of random track access without manual rewinding or flipping. These advantages appealed to enthusiasts seeking a more reliable alternative to analog media, despite the high cost of players, which in the often exceeded $900. By 1983, the industry hailed the arrival as a pivotal moment, with sales accelerating as manufacturing ramped up and more titles became available. In some markets, such as and parts of , CD unit sales began surpassing cassette tapes by the late , fueled by dropping prices and broader distribution. This early growth laid the foundation for the format's dominance in , transforming consumer expectations for playback.

Expansion and peak popularity

Following the initial success of audio CDs in the late 1980s, the format expanded rapidly into data and multimedia applications, diversifying its applications and solidifying its role in consumer electronics. In 1985, Philips and Sony introduced the Yellow Book standard for CD-ROM, adapting the 12-cm optical disc to store up to 650-700 MB of computer data—over 450 times the capacity of contemporary floppy disks—while maintaining compatibility with existing CD players through added drives. This innovation enabled the distribution of software, encyclopedias, and databases on pre-pressed discs, significantly boosting personal computer adoption by providing reliable, high-capacity storage that enhanced PC utility for both professional and home users during the late 1980s and 1990s. The proliferation continued with multimedia extensions, notably the Video CD (VCD) launched in 1993 by , , Matsushita, and , which used compression to deliver approximately 74-80 minutes of standard-definition video and audio per disc. VCDs became a staple in home entertainment, particularly in Central and and the , where affordable players and discs offered a durable, compact alternative to tapes, enabling widespread access to movies and music videos without the degradation of analog media. These variants, alongside and other interactive formats, transformed the compact disc into a versatile platform for entertainment and information, bridging audio playback with emerging delivery. By the late , the compact disc reached its zenith in popularity, dominating sales and markets. Audio CD shipments globally exceeded 1 billion units annually starting in 1992, peaking at 2.455 billion in 2000, while capturing over 80% of the recorded market share worldwide by that year as cassettes and vinyl faded. This era marked a profound cultural shift from analog to digital consumption, with CDs offering superior , , and portability that encouraged collectors to rebuild libraries and integrated seamlessly into portable players and car stereos, redefining listening habits. The format's impact was recognized with the Technical Grammy Award presented to and in 1998 for their contributions to recording technology.

Decline and revival

The decline of the compact disc began in the late 1990s and accelerated through the 2000s, primarily triggered by the emergence of file-sharing services like in 1999, which enabled widespread unauthorized music distribution. This was compounded by the launch of Apple's in 2001, which popularized portable digital music players, and the subsequent rise of legal digital downloads via platforms like , shifting consumer preference away from . Streaming services, including Spotify's U.S. debut in 2011, further eroded demand by offering on-demand access without ownership. In the United States, CD album shipments peaked at 942.5 million units in 2000 but plummeted to 225.8 million by 2010 and fell below 50 million annually by the late , reflecting a 95% overall decline from the peak. Major manufacturers responded to the downturn by curtailing production; for instance, closed its CD manufacturing plant in , in 2011, laying off 300 employees as physical media demand waned. By 2025, the had largely phased out CD players from new vehicles, with major brands like Ford, , and eliminating them from standard infotainment systems in favor of digital interfaces, leaving only niche models from Subaru and as holdouts. Signs of revival emerged in the amid growing interest in physical formats. U.S. CD shipments rose 1.5% year-over-year to 32.9 million units in , generating $541 million in revenue, a modest 0.7% increase. This uptick was driven by among and Gen Z consumers seeking tangible ownership in an era of streaming dominance, as well as superfans purchasing CDs to directly support artists through higher margins on physical sales compared to streams. Affordable , often $5–$10 per disc versus $25–$40 for vinyl, made CDs an accessible entry point, while ongoing vinyl production shortages and escalating costs redirected some collectors to the format. Into 2025, the revival gained momentum with increased reissues of classic albums targeting collector markets, where limited-edition packaging and bonus content appealed to enthusiasts. Rumors of price-fixing surfaced, as major labels consistently priced deluxe CD reissues at $19.98 despite low manufacturing costs under $1.50 per unit, fueling speculation amid the hype. CDs also maintained persistent utility in archival data storage, valued for their write-once permanence and longevity of up to 25 years in controlled environments, serving niche applications in cold storage where digital alternatives like hard drives degrade faster.

Physical details

Construction and materials

The standard compact disc (CD) consists of a 1.2 mm thick injection-molded substrate that forms the base, with a spiral track of microscopic pits molded into its top surface. This substrate provides structural integrity and transparency for penetration during playback. Over the pitted surface, a thin reflective layer of aluminum, typically 50-100 nm thick, is sputtered to enable reflection, enhancing readability. A protective layer of acrylic , approximately 10-20 μm thick, is then applied over the aluminum to shield it from oxidation, dust, and minor abrasions. Data on a CD is encoded in the form of pits and lands (the flat areas between pits) along a single continuous spiral track that begins at an inner radius of 25 and extends outward to an outer radius of 58 , allowing for approximately 5.7 billion bits of storage on a standard 120 disc. These pits measure about 0.5 μm in width and 0.125 μm in depth, with lengths varying from roughly 0.83 μm to 3 μm to represent through transitions between pit and . The track pitch, or spacing between adjacent turns of the spiral, is standardized at 1.6 μm to ensure precise tracking without interference. Playback relies on a semiconductor emitting at a of 780 nm in the near-infrared , which passes through the clear substrate from below and reflects off the aluminum layer. Variations in reflection intensity—caused by the beam interacting differently with pits and lands—are detected by a to decode the . Pressed CDs exhibit high durability, with an expected of 50 to 100 years under recommended storage conditions such as temperatures less than 23°C and relative of 20-50%, though actual longevity can vary based on manufacturing quality and environmental exposure. Resistance to scratches and surface defects is bolstered by the Cross-Interleaved Reed-Solomon Code (CIRC) error correction system, which can interpolate and correct errors from defects up to 2.5 mm in length, such as fingerprints or light abrasions, without audible or visible data loss in most cases. The coating further contributes to scratch resistance by providing a hard, smooth barrier, though severe damage penetrating to the reflective layer can overwhelm error correction capabilities.

Sizes, shapes, and variants

The standard compact disc measures 120 mm in diameter and 1.2 mm in thickness, capable of holding 74 to 80 minutes of audio or 650 to 700 MB of . Variants include smaller formats designed for specific applications. Mini-CDs, with an 80 mm diameter, store approximately 20 minutes of audio or 185 MB of and were developed for portable devices. These 3-inch discs, often used in early portable CD players, require adapters for standard tray-loading mechanisms to ensure compatibility. CDs adopt a rectangular measuring roughly 80 mm by 68 mm, maintaining a central recording area similar to mini-CDs while facilitating promotional or business uses; their non-circular form limits compatibility with some slot-loading drives. Specialized manufacturing variants enhance optical beyond standard dimensions. The SHM-CD (Super High Material CD), introduced in 2007 by and , employs a high-transparency resin originally developed for LCD screens as its substrate. This material reduces and improves penetration at the 780 nm wavelength, minimizing read errors and yielding clearer sound reproduction with higher resolution and reduced distortion. SHM-CDs adhere to the 120 mm standard size and Red Book specifications, ensuring playback on any conventional . Data integrity in these discs is assessed through error rate measurements focused on pit geometry. Testing involves metrics such as Block Error Rate (BLER), which quantifies errors per second, and , the variation in pit and land edge positions; elevated rates indicate degradation in pit shape that compromises readability. Smaller variants like mini-CDs and shapes exhibit heightened vulnerability to edge damage, as scratches or impacts near the perimeter can more readily affect the outer data tracks due to reduced surface area.

Formats and standards

Audio formats

The Red Book standard, established by and , defines the core audio format for compact discs as (CD-DA), utilizing two-channel (PCM) with 16-bit depth and a 44.1 kHz sampling rate to capture audio with a frequency response up to 20 kHz. This format stores audio data in sectors of 2,352 bytes each, read at a constant linear velocity yielding 75 sectors per second, which equates to approximately 4,500 sectors per minute and supports a total capacity of 74 minutes of playback or 650 MB on a standard 120 mm disc. The design prioritizes high-fidelity reproduction while ensuring compatibility across players through robust error correction via Cross-Interleaved Reed-Solomon Code (CIRC). The Cross-Interleaved Reed-Solomon Code (CIRC) serves as the primary error correction mechanism in the CD-DA format, enabling the detection and correction of errors arising from disc imperfections such as scratches, dust, or manufacturing defects. This system integrates Reed-Solomon error-correcting codes with cross-interleaving to effectively manage both random and burst errors. It consists of an outer (28,24) Reed-Solomon code and an inner (32,28) Reed-Solomon code, with interleaving distributed over 109 symbols, equivalent to approximately 2.5 mm on the disc surface. Consequently, CIRC can correct burst errors of up to 3,500 consecutive bits or defects up to 2.5 mm in length, as well as random errors, thereby ensuring reliable playback without audible artifacts and enhancing the overall durability of compact discs. To address demands for higher resolution, and introduced the (SACD) in 2002 as a hybrid disc format, featuring a conventional Red Book layer for with existing CD players alongside a high-density layer encoded in (DSD). DSD employs 1-bit at a 2.8224 MHz sampling rate—64 times that of CD-DA—achieving a frequency bandwidth from DC to 100 kHz and a exceeding 120 dB, which supports both and multi-channel (up to 5.1 surround) audio reproduction. SACD discs maintain the physical dimensions of standard CDs but utilize a translucent recording layer to enable dual-layer construction without altering playback mechanics. In the 1990s, Philips extended the Red Book framework with CD-MIDI, an optional subcode channel format that embeds Musical Instrument Digital Interface (MIDI) sequencer data parallel to the primary PCM audio tracks, allowing compatible hardware to generate and synchronize synthesized music alongside or instead of pre-recorded sound. This enables dynamic playback variations, such as timbre changes or accompaniment generation, while preserving full audio CD compatibility for non-MIDI devices.

Data and video formats

The format, specified in standard of 1988, adapts the compact disc for , providing up to 650 MB capacity on a standard 74-minute disc. It includes two operating modes: Mode 1, which incorporates error correction codes and the for reliable storage of software and text data across multiple operating systems; and Mode 2, which omits some error correction to allow interleaved audio, video, and other multimedia alongside data. This structure made CD-ROM a foundational medium for distributing applications, databases, and encyclopedias in the late and 1990s. The (VCD) standard, detailed in of 1993 and developed by , , , and , brings video to compact discs for home playback. It uses Mode 2, Form 2 of the CD-ROM XA extension to store compressed video at 352×240 resolution () or 352×288 (PAL), paired with Layer II audio, enabling approximately 74 minutes of VHS-equivalent content per disc. VCD gained popularity in and developing markets as an affordable alternative to , supporting playback on modified CD players or dedicated hardware. Super Video CD (SVCD), developed in the late as an enhancement to VCD primarily for the Chinese market, employs video compression to deliver superior quality within the same disc constraints. It targets 480×480 resolution () or 480×576 (PAL) with bitrates up to 2,600 kbps for video—nearly double VCD's—alongside Layer II audio at 224 kbps, allowing about 40–60 minutes of near-DVD quality footage per disc while maintaining backward compatibility with VCD players. This format improved color fidelity and motion handling but saw limited global adoption due to the rise of DVD. Kodak's Photo CD system, announced in , digitizes photographic prints, negatives, or slides onto compact discs for archival and display purposes. Images are scanned at high resolution (up to 2,048×3,072 pixels for ) and stored in the proprietary Kodak PhotoYCC color space, a variant optimized for photographic reproduction with extended for negatives. Each disc holds up to 100 images across six progressive resolutions, from thumbnail (128×192) to full (2,048×3,072), enabling flexible viewing on computers using compatible software, such as Kodak's plug-ins or third-party applications, or on Kodak's dedicated players.

Interactive and enhanced formats

The Compact Disc Interactive (CD-i), specified in the Green Book standard, was co-developed by and in as a platform enabling interactive applications such as video playback, educational content, and gaming on dedicated hardware. This format extended the data mode by integrating audio, text, graphics, and , allowing users to navigate content via a controller connected to a television. CD-i players featured a 16/32-bit 68070 processor running at 15.5 MHz, 1 MB of RAM, and a single-speed (1x) CD drive to support real-time interactivity without buffering delays. In 1991, introduced CD-i Ready, a hybrid format that embedded interactive tracks within the pre-gap pause sectors before the first audio track on a standard CD, enabling playback of both music and hidden elements like biographies, videos, and mini-games when used with a compatible CD-i player and TV setup. This design ensured compatibility with conventional audio CD players, which would skip the pre-gap data and play only the audio portion, while CD-i systems could access the interactive content for enhanced user experiences tied to the music. The Enhanced Music CD, also known as CD+ or CD-Extra and defined in the Blue Book standard, was established by and in May 1995 to combine a primary audio session with a secondary session on a single disc, allowing CD-ROM drives to deliver supplementary interactive elements such as , artist videos, photos, or web links alongside standard audio playback. Unlike earlier mixed-mode discs, this multisession approach separated audio (following Red Book specs) from (Yellow Book compliant) to prevent interference, with the audio session read first by all players and the data session accessible only on computers for user-driven exploration. VinylDisc, introduced in the mid-2000s by the German firm Optimal Media Production, represented a novel hybrid format bonding a standard layer on one side with playable vinyl grooves on the opposite surface, enabling approximately three minutes of analog audio from the vinyl while offering full digital capacity for extended playback. This design catered to audiophiles seeking a fusion of analog warmth and digital convenience in a single 12 cm , though production remained limited due to manufacturing complexities.

Manufacturing and economics

Production process

The production of read-only compact discs (CDs) begins with the mastering process, where , typically in Disc Description Protocol (DDP) format, is used to create a glass master disc. A clean, polished glass substrate, approximately 240 mm in diameter, is coated with a thin layer of material via spin-coating and then baked to stabilize it. A high-precision laser beam recorder (LBR), often using an argon-ion or laser with a around 351-488 nm, exposes the photoresist in a spiral track, creating a pattern of pits and lands that represent the ; pit lengths range from 0.833 to 3.056 micrometers, corresponding to the CD's error correction and encoding standards. The exposed photoresist is then developed chemically, revealing the etched pattern on the glass master, which serves as the template for replication. Next, electroforming produces durable metal stampers from the glass master. The master is first metallized with a thin conductive layer, such as silver or nickel-vanadium alloy, via or chemical deposition in a environment. This layer is then immersed in an electroforming bath containing nickel sulfamate, , and nickel chloride solutions, where an deposits a thick nickel layer (typically 300 micrometers) onto the master over several hours, forming a negative image of the pits and lands. The father stamper is separated from the , polished, and punched to the standard 130 mm ; additional steps may create and stampers to increase production capacity, with each stamper capable of molding thousands of discs. This process ensures in replicating the microscopic features, though yields for stampers historically ranged from 60-80% due to manual handling sensitivities. The replication stage involves injection molding to form the polycarbonate substrate. Multiple stampers are mounted in an industrial , where polycarbonate pellets are melted at approximately 300-330°C and injected under (around 60 tons clamping force) into the mold cavity for 1-2 seconds, pressing the molten against the stamper to imprint the pit . The mold is maintained at about 85-120°C to control cooling, solidifying the 1.2 mm thick disc in 2-4 seconds before ejection. This cycle repeats rapidly, enabling high-volume output. Following molding, the disc's pitted surface is metallized by a reflective aluminum layer (50-100 nm thick) in a using ions and high-voltage discharge, enhancing reflectivity for reading. Finally, protective and labeling steps complete the disc, accompanied by rigorous quality control. A thin layer of acrylic lacquer is spin-coated onto the aluminum surface at high speed (up to 3000 rpm) to protect against oxidation and scratches, then cured with light; this layer is typically 5-10 micrometers thick. Labels are applied via or offset methods using UV-curable inks in CMYK colors, dried instantly under UV lamps. involves 100% for defects like bubbles or warpage using vision systems, plus electronic testing on a sample basis (about 1 in 1000 discs) in simulated players to verify and error rates below the CD standard's Reed-Solomon correction threshold. Modern facilities achieve yields exceeding 99%, minimizing waste through inline monitoring and process automation. The resulting disc structure—polycarbonate substrate, aluminum reflector, and lacquer overcoat—enables reliable optical readout. The manufacturing cost of compact discs has decreased substantially since their introduction, driven by and advancements in production technology. In the , the cost to manufacture a single CD ranged from $3 to $4 per unit due to limited facilities and high initial setup expenses. By the , costs had stabilized around $4.50 per unit for smaller runs but began declining with expanded global capacity. In 2025, bulk production costs have fallen to $0.50–$1.00 per disc, reflecting optimized processes and high-volume output from specialized plants. Retail prices for CDs have followed a downward trajectory as production efficiencies improved and market competition intensified. At launch in , CDs typically retailed for $15–$20, positioning them as a premium alternative to vinyl and cassettes. During the 1990s, as the format gained dominance, prices settled at $10–$15 for standard albums, supported by widespread adoption and reduced manufacturing overheads. By 2025, amid a nostalgic revival, average retail prices range from $5–$10, particularly for reissues and collector editions, though premium releases can exceed this. Global CD production reached its zenith in 2000, with approximately 2.455 billion units shipped worldwide, fueled by the format's peak popularity in audio and data applications. Production volumes have since contracted sharply; 2025 estimates place annual output at 400–500 million units, concentrated on audio reissues, archival releases, and niche markets like . Key economic factors shaping the CD industry include a pronounced shift in the to , where low-cost labor and robust infrastructure have consolidated . Firms such as Replication Asia and PrimeDisc in now dominate global output, enabling cost reductions through efficient, high-capacity facilities. The proliferation of digital streaming has further influenced pricing by eroding demand for , prompting manufacturers and labels to lower prices to sustain sales among dedicated collectors and in emerging markets. This dynamic contributed to a 6.1% decline in CD revenues in 2024, part of broader physical format trends totaling $4.8 billion globally.

Recordable and rewritable media

Recordable CDs

Recordable CDs, designated as (Compact Disc-Recordable), represent a write-once format introduced to enable permanent data recording on compact discs compatible with existing CD playback systems. The foundational standard for CD-R was established in the Orange Book Part II, published by and in November 1990, which specifies the Compact Disc Write Once (CD-WO) system for creating pits through laser-induced changes in a recording layer. At the core of CD-R technology is an organic layer, typically , , or azo-based, applied over a substrate with a pre-grooved spiral track. During the , a high-power (operating at 775–800 nm and 4–8 mW optimum power) pulses to heat and deform specific areas of the dye, rendering them opaque and non-reflective to simulate the pits and lands of a standard pressed CD; this or melting effect ensures the recorded disc maintains reflectivity levels above 65% for . The process uses constant linear velocity (CLV) control, with the laser modulated via an (n-1) strategy to form pits of varying lengths, optimized through an initial power (OPC) procedure to minimize below 30 ns. CD-R discs support recording speeds from 1x (1.2–1.4 m/s linear velocity) up to 52x, depending on the media and drive capabilities, with standard capacities of 650 MB (equivalent to 74 minutes of audio) or 700 MB (80 minutes) in the 120 diameter format. These discs are commonly applied for data backup, software distribution, and personal music compilation, allowing users to create custom audio CDs or store files in format. Compatibility with conventional CD-DA players and ROM drives is achieved via the Absolute Time In Pregroove (ATIP) system, which embeds addressing, timing, and media type information (at 3150 bits/sec using biphase-mark modulation) in the wobble of the pregroove, enabling seamless navigation without dedicated hardware changes. Durability of CD-R media varies by dye type and storage conditions, with accelerated aging studies estimating life expectancies exceeding 30 years for most formulations under controlled environments (e.g., 40°C and 40% relative humidity), though dyes may degrade faster than variants. Degradation primarily results from exposure, which breaks down the organic and increases error rates, or from humidity-induced oxidation; proper storage in opaque jewel cases away from direct sunlight and temperature fluctuations can extend usability to 50–100 years or more.

Rewritable CDs

Rewritable compact discs, known as , were standardized in Part III, published in 1996 by and , which defines the format for erasable and rewritable optical media compatible with existing CD systems. The core technology relies on a phase-change recording layer composed of a alloy, typically Ag-In-Sb-Te, where heating induces reversible transitions between crystalline (reflective) and amorphous (less reflective) states to form and erase pits representing . This allows multiple write-erase cycles, typically up to 1,000 times per disc, enabling data overwriting without permanent alteration, unlike the organic dye-based mechanism in discs. CD-RW discs operate at writing speeds ranging from 1x to 10x, corresponding to approximately 0.15 MB/s to 1.5 MB/s, which is generally slower than contemporary CD-R speeds that reached up to 52x due to the more precise control required for phase transitions. Their reflectivity, measured at 15-25% in the recorded state, is lower than the 40-70% of standard CDs or , necessitating MultiRead-compliant drives for broad compatibility; older CD audio players often struggle with playback because their lasers expect higher reflection levels. Primarily, CD-RW discs serve applications requiring iterative data handling, such as temporary backups, , and test authoring for production, where frequent revisions are common. They function as an intermediate storage solution between volatile online memory and permanent archival media, supporting data capacities of 650-700 MB per disc for tasks like transporting files or versioning content. Despite these advantages, CD-RW media exhibit limitations including a shorter practical lifespan of 5-10 years for unrecorded discs under normal conditions, attributed to material degradation in the phase-change layer, compared to longer durations for . Additionally, their higher production complexity results in elevated costs, historically around $1-2 per disc versus $0.20 for equivalents in the early , limiting widespread adoption for non-rewritable needs.

Copy protection and security

The original Compact Disc (CD) format, particularly for audio (CD-DA), included no built-in digital copy protection, as the Red Book standard focused on playback fidelity rather than restricting duplication. However, to mitigate concerns over home copying, the (RIAA), along with and , developed the Serial Copy Management System (SCMS) in 1987. SCMS operates at the digital interface level, using subcode bits in protocols like and AES/EBU to permit one generation of digital copies from a protected source (e.g., a commercial CD to a digital recorder) while flagging copies to prevent further digital duplication. This system became mandatory for (DAT) recorders and was widely adopted in CD players and recorders by the early 1990s, though it did not affect analog copying. As personal computers and drives proliferated in the late 1990s, record labels introduced proprietary technologies on pressed audio CDs to impede and exact duplication. These schemes often exploited differences between audio CD players (which use robust error correction) and drives (which require precise data reads). A notable example is Cactus Data Shield (CDS), developed by Midbar Technologies (acquired by Macrovision in 2001), which embeds intentional and non-standard sectors that audio players can tolerate via cross-interleaved Reed-Solomon coding (CIRC) but cause extraction errors in software like Exact Audio Copy. CDS was used on millions of CDs from labels like and Warner starting around 2000, though it could interfere with legitimate uses such as playback on computers or car stereos. Other systems included SunnComm's MediaMax, which installed software to limit burns, and Sony's XCP, both aimed at restricting copies to a few per disc. These protections led to significant controversies, most prominently the 2005 Sony BMG rootkit scandal. Sony's XCP and MediaMax implementations on over 20 million CDs secretly installed software on Windows PCs upon insertion, hiding the protection files, monitoring user behavior, and blocking unauthorized copying—without disclosure or user consent. The created exploitable security vulnerabilities, allowing malware to evade detection and potentially compromising system stability. Following public backlash, lawsuits from the (EFF) and others, and investigations by authorities including the U.S. , Sony BMG recalled affected titles, offered exchanges for unprotected CDs, and paid settlements exceeding $100 million. The incident accelerated the abandonment of disc-based schemes, shifting industry focus toward (DRM) in downloads and streaming. For data storage formats like , security typically relies on application-level encryption (e.g., via extensions or software like CSS for video CDs) rather than format-inherent protections, allowing flexible implementation for confidentiality and .

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