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 mm and typically hold up to 74 minutes of audio or approximately of data. This was later regularly extended to 80 minutes or by reducing the spacing between data tracks, with some discs unofficially reaching up to 99 minutes or which falls outside established specifications. Smaller variants, such as the Mini CD, range from 60 to 80 mm 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
Physical details
A CD is made from 1.2 mm thick, polycarbonate plastic, and weighs 14–33 grams.[4] 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.
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.[5] The distance between the windings (the pitch) is 1.6 μm (measured center-to-center, not between the edges).[6]
Logical format
Audio CD
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.[23] 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.
Manufacture, cost, and pricing
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.[24] 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.[24] 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.[25]
Writable compact discs
Recordable CD
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.[26] Testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions. This failure is known as disc rot, for which there are several, mostly environmental, reasons.[27]
Copy protection
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, 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
- Comparison of popular optical data-storage systems
- Optical disc packaging
- Extended Resolution Compact Disc
- List of optical disc manufacturers
Further reading
- Ecma International. Standard ECMA-130: Data Interchange on Read-only 120 mm Optical Data Disks (CD-ROM), 2nd edition (June 1996).
- Pohlmann, Kenneth C. (1992). The Compact Disc Handbook. Middleton, Wisconsin: A-R Editions. ISBN 0-89579-300-8.
- Peek, Hans et al. (2009) Origins and Successors of the Compact Disc. Springer Science+Business Media B.V. ISBN 978-1-4020-9552-8.
- Peek, Hans B., The emergence of the compact disc, IEEE Communications Magazine, Jan. 2010, pp. 10–17.
- Nakajima, Heitaro; Ogawa, Hiroshi (1992) 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.
External links
- Video How Compact Discs are Manufactured
- CD-Recordable FAQ Exhaustive basics on CD-Recordable's
- 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) – Sony website in Japanese
- Popularized History on Soundfountain
- A Media History of the Compact Disc (1-hour podcast interview)
References
- The Compact Disc (CD) is Developed historyofinformation.com, retrieved 9 February 2023^
- U.S. Music Revenue Database RIAA, retrieved 2024-03-17^
- Dorian Lynskey. How the compact disc lost its shine