Compact disc

This may be in large degree due to its status as a Philips trademark under that spelling. The digital clock was invented in 1956. Notwithstanding the variability of general usage between "disk" and "disc" [3], the customary spelling is "compact disc", rather than "compact disk". Quartz timepieces were invented in the 1920s. Not all players allow this. The Noon gun in Cape Town still fires an accurate signal to allow ships to check their chronometers. To hear the hidden track, the listener must usually "rewind" the player past the beginning of the first listed track. John Harrison created the first, highly accurate marine chronometers in the mid-18th century.

In this case, the hidden track is an unlisted track sandwiched between the two. This need was a major motivation for the development of accurate mechanical clocks. On most discs, the location of the first track listed in the table of contents immediately follows the table of contents itself. Latitude is fairly easy to determine through celestial navigation, but the measurement of longitude requires accurate measurement of time. Other discs hide the extra material at the beginning of the disc. Accurate navigation by ships beyond the sight of land depends on the ability to measure latitude and longitude. Either way, the hidden portion is heard when the disc is played to the end. Rather, they are designated as the current ideal clock because they are currently the best instantiation of the definition.

These may be an extension of the last audio track or a separate track hidden from the disc's table of contents. However, they are not so designated by fiat. Some commercially released audio discs have a "secret" bonus track. Since atoms are so numerous and since, within current measurement tolerances, they all beat in a manner such that if one is chosen as periodic then the others are all deemed to be periodic also, it follows that atomic clocks represent ideal clocks to within present measurement tolerances and in relation to all presently known physical processes. This is commonly referred to as the analog hole. While not all physical processes can be surveyed, the definition should be based on the set of physical processes which includes all individual physical processes which are proposed for consideration. Any loss of sound quality caused by this method is generally considered negligible. This definition can be further improved by the consideration of successive levels of smaller and smaller error tolerances.

In any case, even if a disc cannot be directly ripped, it can still be played in audio mode, and the audio thence captured. Sometimes that signal alone is (confusingly) called "the clock," but sometimes "the clock" includes the counter, its indicator, and everything else supporting it. Other systems developed are Macrovision CDS-200 and Mediamax CD-3. The recurrent, periodic process (a metronome) is an oscillator and typically generates a clock signal. The reason for this reuse is cost efficiency. This leads to the following definitions:. in car radios, have problems playing copy-protected media, mostly because they use hardware and firmware components also used in CD-ROM drives. An ideal clock is more appropriately defined in relationship to the set of all physical processes.

Also, many ordinary CD audio players, e.g. Therefore, to define an ideal clock in terms of any physical theory would be circular. For example, audio tracks on such media cannot be easily added to a personal music collection on a computer's hard disk or a portable (non-CD) music player. An ideal clock is a scientific principle that measures the ratio of the duration of natural processes, and thus will give the time measure for use in physical theories. However, there has been great public outcry over copy-protected discs because many see it as a threat to fair use. Some computers also maintain time and date for all manner of operations whether these be for alarms, event initiation or just to display the time of day. It also seems likely that Philips' new models of CD recorders will be designed to be able to record from these "protected" discs. (A few research projects are developing CPUs based on asynchronous circuits).

Philips has stated that such discs are not permitted to bear the trademarked Compact Disc Digital Audio logo because they violate the Red Book specification. Practically all computers depend on an accurate internal clock signal to allow synchronized processing. This is intended to prevent the data track from being ripped, but can be defeated by ignoring the table of contents and reading the disc sector by sector. an alarm clock, a VCR, or a time bomb (see: counter). Another copy protection method places a data track (usually containing bonus software for computer users) at the end of the disc and gives it an invalid size in the disc's table of contents. It may also be used to control a device according to time, e.g. These discs are said to be more sensitive to disc pollution or surface damage (typically in the form of scratches) because they partially exhaust the error-correction thresholds incorporated into the Red Book standard right from the time of production. The main purpose of a clock is not always to display the time.

Some of these deliberately introduced error patterns into audio tracks severe enough to defeat the error-correcting code (and hence defeat most CD-ROM drives attempting to copy the tracks as data), but not so disruptive as to prevent interpolation from working (hence allowing the same tracks to be played in audio mode without overly affecting fidelity). A small clock is often shown in a corner of computer displays or mobile phones. Starting in early 2002, attempts were made by record companies to market "copy-protected" compact discs. a train station or church. Where error correction fails on larger defects, audio CD players are expected to apply interpolation algorithms to conceal the loss of audio data. Clocks are in homes and offices; smaller ones (watches) are carried; larger ones are in public places, e.g. An error-correcting code is included with Red Book audio to deal with small scratches or defects on the disc media.
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Ripping is the process by which the contents of an audio disc is copied out verbatim to a duplicate disc or re-encoded into some other format, such as MP3 or Ogg Vorbis. After a reset digital clocks lacking a backup battery either start counting from 00:00, or stay 00:00 to indicate that their time needs to be set. The Red Book audio specification does not include any copy protection mechanism. Mains-driven digital clocks are often reset after a power failure, and, typically, begin flashing to alert us that the time they display is incorrect. A CD-RW does not have as great a difference in the reflectivity of lands and bumps as a pressed CD or a CD-R, and so many CD audio players cannot read CD-RW discs, although the majority of standalone DVD players can. A digital clock typically displays a numerical hour range of 0-23, or 1-12 (with an indication of AM or PM) using an LCD or LED display, although digital versions of analog-style faces exist. The write laser in this case is used to heat and alter the chemical properties of the alloy and hence change its reflectivity. Digital clocks use electronic methods of keeping time, typically the 50 or 60 hertz oscillation of AC power or a crystal oscillator as in a quartz movement.

CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The ultimate analog clock is the sundial, which tracks the sun continuously, registering the time by the shadow of its gnomon. The resulting discs can be read by most CD-ROM drives and played in most audio CD players. The analog clock with digital display emulates a digital clock but with an analog movement. CD-R recordings are permanent. It usually has a circular scale of 12 hours, which also serves as a scale of 60 minutes, and often also as a scale of 60 seconds. The write laser of the CD recorder changes the characteristics of the dye to allow the read laser of a standard CD player to see the data as it would an injection molded compact disc. A clock face is the part of an analog clock that tells time through the use of a fixed numbered dial or dials and moving hand or hands.

A photosensitive dye is then applied, and then the discs are metallized and lacquer coated. Analog clocks may be mechanical or have a quartz movement. Recordable compact discs are injection molded with a "blank" data spiral. There are two major types of clocks. The disc is then metallized with aluminum and lacquer coated. Even mechanical clocks have since come to be largely powered by batteries, removing the need for winding. Polycarbonate is liquified and injected into the mold cavity where the stamper transfers the pattern of pits and lands to the polycarbonate disc. Time in these cases is measured in several ways, such as by the behaviour of quartz crystals, or the decay of radioactive elements.

It is then plated to make a positive version of the CD. The development of electronics in the twentieth century led to clocks with no clockwork parts at all. This dye is then etched, leaving the data track. Terry is known as the founder of the American clock-making industry. A "stamper" is made from the original media (audio tape, data disc, etc.) by writing to a glass disc (referred to as a glass master) coated with a photosensitive dye with a laser. On November 17, 1797, Eli Terry received his first patent for a clock. Injection moulding is used to mass produce compact discs. It was also at this time that clock cases began to be made of wood and clock faces to employ enamel.

However, in 1985 Yellow Book CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. The English clockmaker William Clement, inventor of the anchor escapement, is credited with developing this form in 1670. For its first few years of existence, the compact disc was purely an audio format. Notably, the longcase clock (aka grandfather clock) was created to house the pendulum and works.
. The excitement over the pendulum clock attracted the attention of designers resulting in a proliferation of clock forms. The originally CD-only label Ryko extended this system to the other media when it began making LPs and cassettes so that a digital recording on an LP would be DDA, and so forth. Within just one generation, minute hands and then second hands were added.

A notable example is Herb Alpert's Rise album from 1979. In 1670, the English clockmaker William Clement created the anchor escapement, an improvement over Huygens' crown escapement. A few examples of DAD recordings exist, mostly of works that were originally recorded digitally but later remixed by artists who preferred to work with analog technology. He determined the mathematical formula that related pendulum length to time (99.38 cm or 39.13 inches for the one second movement) and had the first pendulum driven clock made. Two examples from 1982 are Signals by Rush and The Nightfly by Donald Fagen. Christiaan Huygens, however, is usually credited as the inventor. By the time the compact disc was introduced worldwide digital recording and mixing was becoming commonplace among recording artists and producers known for their interest in fidelity. Galileo had the idea to use a swinging bob to propel the motion of a time telling device earlier in the 17th century.

An early example of an analog recording that was digitally mixed is Fleetwood Mac's 1979 release Tusk. The next major development in accuracy occurred in 1657 with the invention of the pendulum clock. Martin used digital mixing, however, to eliminate the distortion and noise that an analog master tape would introduce (thus ADD). The dial between the hour markers is divided into four equal parts making the clocks readable to the nearest 15 minutes. Others, such as former Beatles producer George Martin, felt that the multitrack digital recording technology of the early 1980s had not reached the sophistication of analog systems. These clocks have only one hand. Stevie Wonder adopted the technology in early 1979 for Journey Through the Secret Life of Plants and used it on all later recordings. The earliest table clocks that survive in any quantity are mid-16th century ones from the metalworking towns of Nuremberg and Augsburg.

Many other top recording artists were early adherents of digital recording. Canonical hours differ in length, and varied as the times of sunrise and sunset shifted. It was unmixed, being recorded straight to a two-track 3M digital recorder in the studio. These were used to announce the canonical hours or intervals between set times of prayer. The first digitally recorded (DDD) popular music album was Ry Cooder's Bop Till You Drop, recorded in late 1978. The earliest reasonably accurate clocks are the 13th century tower clocks probably developed for (and perhaps by) monks in Northern Italy. (Unmixed analog recordings are likewise usually described as ADD to denote a single generation of analog recording). The Muslims also constructed a variety of highly accurate astronomical clocks for use in their observatories.

These unmixed digital recordings are still described as DDD since the technology involved is purely digital. In addition, during the 9th century, Ibn Firnas of Islamic Spain, according to Will Durant, invented a watch-like device which kept accurate time. In most cases there was no mixing stage involved; a stereo digital recording was made and used unaltered as the master tape for subsequent commercial release. The latter type was directly copied by Europeans during the 15th century. The first 16-bit PCM recording in the United States was made by Thomas Stockham at the Santa Fe Opera in 1976 on a Soundstream recorder. One such clock included a mercury escapement. Commercial digital recording of classical and jazz music began in the early 1970s, pioneered by Japanese companies such as Denon, although experimental recordings exist from the 1960s. Designs and illustrations of epi-cyclic and segmental gears were provided.

Often this code was accompanied by a short description such as "Full Digital Recording" for DDD and "Digitally Mixed Analog Recording" for ADD. These clocks were weight-driven. Almost all early CDs are "AAD" (analog recording and mixing, digital transfer to CD) as a result. A variety of mechanical clocks were produced by Spanish Muslim engineers, both large and small, and this knowledge was transmitted to Europe through Latin translations of Islamic books on mechanics. The first letter represents how the album was recorded, the second how it was mixed, and the third how it was transferred (inevitably a D, as the CD is a digital medium). This word has led scholars to believe that these tower clocks did not employ hands or dials, but “told” the time with audible signals such as bells. Many CDs, especially classical music and many popular recordings, come with a three-letter code printed on the back known as the SPARS (acronym for Society of Professional Audio Recording Studios) Code, where "A" stands for analog and "D" stands for digital. (from Greek hora, hour, and legein, to tell).

Note that the CD+G or “karaoke” extension also uses the R-W subchannels or subcodes to store low resolution graphics. There is a record that in 1176 Sens Cathedral installed a ‘horologe’—the word still used in French for large clocks. ITTS is also used by Digital Audio Broadcasting or the MiniDisc. By the 9th century AD a mechanical timekeeper had been developed that lacked only an escapement mechanism. The text is stored in a format usable by the Interactive Text Transmission System (ITTS). Historians disagree over the Antikythera mechanism but this is largely thought to be an early mechanical clock. About 31 megabytes of information can be stored there. The historian Vitruvius reported that the ancient Egyptians also used a clepsydras, a time mechanism run by flowing water.

The information is stored in the lead-in area of the CD, where there is roughly five kilobytes of space available, or in the R through W Subchannels on the disc, which are not used by strict Red Book CDs. In an hourglass fine sand pours through a tiny hole at a predictable rate. album name, song name, and artist) on a standards-compliant audio CD. Candles and sticks of incense which burn down at approximately predictable speeds have also been used as clocks. It allows for storage of additional information (e.g. The sundial, which measures the time of day by the direction of shadows cast by the sun, was widely known in ancient times. CD-Text is part of the CD+G extension to the Red Book standard for audio CDs. As the seasons and the phases of the moon can be used to measure the passage of longer periods of time, shorter processes could be used to measure off hours and minutes.

Channels R…W are unused by Red-Book compliant CDs, and have been used for extensions to the standard. In principle, it requires no more than some physical process which will proceed at a known rate, and a way to gauge how long that process has been continuing. The ISRC is used by the media industry, and contains information about the country of origin, the year of publication, owner of the rights, as well as a serial number, and some additional tags:. The clock is one of the oldest human inventions. It contains positioning information, the Media Catalog Number (MCN), and International Standard Recording Code (ISRC). . Channel Q is used for control purposes of more sophisticated players. The clock in its most common modern form (in use since at least the 14th century) displays the hours, minutes, and sometimes seconds that pass over a twelve or twenty-four-hour period.

Quite a few players ignore it in favor of the Q Channel. A portable clock is called a watch. Channel P is a simple pause/music flag, which can be used for low-cost search systems. (Usually, for measuring time of intervals less than a day--as opposed to a calendar.) Those used for technical purposes, of very high accuracy, are sometimes called chronometers. These streams are called "channels", and are labeled starting with the letter P, like so:. A clock (from the Latin cloca, "bell") is an instrument for measuring time. Each of these bits corresponds to a separate stream of information. world clock.

Each of the 96 subchannel data bytes can be thought of as being divided into eight bits. water clock. 1 byte for command, 1 byte for instruction, 2 bytes for parityQ, 16 bytes for data, and 4 bytes parityP. watch. The 96 bytes of subchannel information in each sector contain four packets of 24 bytes apiece:. time clock. In each sector there are 2352 bytes (24×98) of audio content data and 96 bytes of subchannel data. tide clock.

Thus each channel has a bit rate of 7.35 (=44.1/6) kbit/s. sundial. The eight bits are used as eight different subcoding channels, and given letters designating their usage: P, Q, …, W. striking clock. The eight bits of a subcode byte are available for control and display. stopwatch. A frame comprises 33 bytes, of which 24 are audio bytes (six full stereo samples), eight error correction, CIRC-generated, bytes plus one subcode byte. skeleton clock.

The data in a CD are arranged in frames. sidereal clock. Besides digital audio, a CD contains digital data called "subcode", which is multiplexed with the digital audio. quartz clock. ... projection clock. An audio CD has a very different structure:. torsion pendulum clock.

A CD-ROM (data) sector contains 2352 bytes:. swinging pendulum clock. A 1x speed CD drive reads 75 consecutive sectors per second. pedestal clock. The playing time is 74 minutes, or 4440 seconds, so that the net capacity of a Mode-1 CD-ROM is 682 MB. mantel clock. The net byte rate of a Mode-1 CD-ROM is 44.1k×2048/(6×98) = 153.6 kB/s. longcase clock.

In a Mode-2 CD-ROM, which is mostly used for video files, there are 2336 user-available bytes per sector. hourglass. A Mode-1 CD-ROM, which has the full third layer error correction capability, contains a net 2048 bytes of the available 2352 per sector. grandfather clock. Note that the CIRC error correction system used in the CD audio format has two interleaved layers. game clock. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed-Solomon error correction. flip clock.

The CD-ROM is in essence a data disc, which cannot rely on error concealment, and it requires therefore a higher reliability of the retrieved data. cuckoo clock. A CD-ROM sector contains 98 frames, and holds 98×24 = 2352 bytes. countdown clock. The synchronization word cannot occur in the normal bit stream, and can thus be used to identify the beginning of a frame. Railroad chronometers. A 27-bit unique synchronization word is added, so that the number of channel bit in a frame totals 588. doll's head clock.

In total we have 33*(14+3) = 561 channel bits. Data clock for timescapes created with time-technology. The eight bits of a subcode byte are available for control and display. clock network. A frame comprises 33 bytes, of which 24 are audio bytes (six full stereo samples), eight error correction, CIRC-generated, bytes plus one subcode byte. chiming clock. Data in a CD-ROM are organized in both frames and sectors. cartel clock.

2×2×6 = 24 bytes. bracket clock. A frame can accommodate six complete 16-bit stereo samples, i.e. binary clock. The smallest entity in the CD audio format is called a frame. atomic clock. Each 14-bit EFM word alternates with a 3-bit merging word. astronomical clock.

Each 14 consecutive bits are grouped and decoded using Eight-to-Fourteen Modulation to get a byte. analog clock with digital display. As bit-times are counted off, a transition (pit-to-land, or land-to-pit) is interpreted as a "1" bit, while a constant region (all-land or all-pit) is interpreted as a "0" bit. alarm clock. Under a microscope, all that is visible is a series of various-sized pits arranged in a long spiral, starting near the inner hole. An ideal clock is a clock (i.e., recurrent process) that makes the most other recurrent processes periodic. A "4.7 GB" DVD has a nominal capacity of about 4.38 GiB. A good clock is one which, when used to measure other recurrent processes, finds many of them to be periodic.

But DVD capacities are given in decimal units. A clock is a recurrent periodic process and a counter. A "700 MB" (or "80 minute") CD has a nominal capacity of about 700 MiB. CD capacities are always given in binary units. However, attempts to combine double LPs onto one CD occasionally resulted in an opposing situation in which the CD would actually offer fewer tracks than the LP equivalent.

CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. The 74-minute playing time of a CD, being more than that of most long-playing vinyl albums, was often used to the format's advantage during the early years when CDs and LPs vied for commerical sales. However, these discs can cause problems in playback when the end of the disc is reached. Another technique to increase the capacity of a disc is store data in the lead out groove that is normally used to indicate the end of a disk, and an extra minute or two of recording is often possible.

This is the limit for most conventional audio CDs today. Using a linear velocity of 1.2 m/s and a track pitch of 1.5 micrometre leads to a playing time of 80 minutes, or a capacity of 700 MB. A disc with data appearing slightly more densely is allowable. If the disc diameter were 115 mm, the maximum playing time would have been 68 minutes, i.e., six minutes less.

With a scanning speed of 1.2 m/s, the playing time is 74 minutes, or around 650 MB of data on a CD-ROM. The program area is 86.05 cm², so that the length of the recordable spiral is 86.05/1.6 = 5.38 km. The main parameters of the CD (taken from the September 1983 issue of the compact disc specification) are as follows:. The Sony PCM-1610 and PCM-1630 are well known examples of PCM adaptors used in conjunction with the Sony U-matic VCR.

There was a long debate over whether to use 14 or 16 bit samples and/or 44,056 or 44,100 samples/s when the Sony/Philips task force designed the compact disc; 16 bits and 44.1 kilo-samples/s prevailed. This system could either store 14-bit samples with some error correction, or 16-bit samples with almost no error correction. Similarly PAL has 294 lines and 50 fields, which gives 44,100 samples/s. A standard NTSC video signal has 245 usable lines per field, and 59.94 fields/s, which works out at 44,056 samples/s.

This technology could store six samples (three samples per each stereo channel) in a single horizontal line. A device that turns an analog audio signal into PCM audio, which in turn is changed into an analog video signal is called a PCM adaptor. The sampling rate of 44.1 kHz is inherited from a method of converting digital audio into an analog video signal for storage on video tape, which was the most affordable way to store it at the time the CD specification was being developed. Reed-Solomon error correction allows the CD to be scratched to a certain degree and still be played back.

In broad terms the format is a two-channel (four-channel sound is an allowed option within the Red Book format, but has never been implemented) stereo 16-bit PCM encoding at a 44.1 kHz sampling rate. Philips is responsible for the licensing program of the intellectual property pertinent to the Compact Disc including the "Compact Disc Digital Audio" logo that appears on the disc. The format of the audio disc, known as the "Red Book" / Sony standard, was laid out by Sony and Philips in 1981. Bulk packaging can be done before or after printing.

Sometimes the spindle of 150 discs are shrinkwrapped together in bulk. The finished assembly has security stickers applied, and is shrinkwrapped with marketing stickers applied. Printing and Packaging: The label is printed onto the disc using a one to six color process (in the case of silk screening), then the printed discs are loaded into a packaging macine that combines a jewel box, tray card, the disc, and booklet. The discs are sampled by QC to ensure quality product.

A laquer is spin coated onto the disc and the disc is tranfered to a spindle. At this point the disc is clear, so a coating of aluminum or gold is applied to the disc for reflectivity. The chamber opens and a robotic arm grabs the disc and transfers it to the next stage. Melted polycarbonate resin is injected into the chamber and the CD is pressed using up to 40 tons of pressure.

Pressing: Each stamper is mounted in an injection moulding machine. This process is also done in a clean room environment. Each stamper is quality checked. Multiple stampers can be made from one glass master.

Stamper Process: Next the glass master is used to create nickel stampers using an electroplating technique. The glass master produced is quality checked before it moves to the next stage. Source material is encoded into the appropriate format whereupon a computer controlled machine "burns" the pits into the emulsion layer of the glass master. The glass is coated with an emulsion.

The nickel is transfered by exciting the nickel to a plasma state whereupon a thin layer of nickel will adhere to the glass. Mastering Process: First, in a clean room, a glass master is prepared by coating a perfectly flat piece of half inch thick circular glass with a layer of nickel. Discs are consequently much easier to ruin by scratching the label side, whereas clear-side scratches can be repaired by refilling them with plastic of similar index of refraction. Pits are much closer to the label side of a disc so that defects and dirt on the clear side can be out of focus during playback.

Most CD manufacturers, dependent on the exact pit geometry such as the slope of the pit edges etc, choose a pit depth of around 90-100 nm, (which is around λ/6n) yielding a sound trade-off between the quality of the push-pull radial tracking and full aperture detection signal. For a maximum push-pull radial tracking signal the best choice is λ/8n = 65 nm. For a maximum full aperture signal, the optimum pit depth is λ/4n = 130 nm (refractive index n=1.5, λ=780 nm). However, the Red Book implicitly specifies the pit depth by specifying the strength of both the push-pull radial tracking signal and full aperture detection signal.

It specifies that the pit depth should be less than (and, thus, not equal) 130 nm. Figure 1, page 8a, of the Red Book specifies many mechanical parameters including the pit depth. This in turn is decoded by reversing the Eight-to-Fourteen Modulation used in mastering the disc, finally revealing the raw data stored on the disc. Instead a change from pit to land or land to pit indicates a one, while no change indicates a zero.

The pits and lands themselves do not represent the zeroes and ones of binary data. By measuring this intensity with a photodiode, one is able to read the data from the disc. The destructive interference thus reduces the intensity of the reflected light compared to when the laser is focused on just a land. The difference in height between pits and lands is one quarter to one sixth of the wavelength of the laser light, leading to a half-wavelength or less phase difference between the light reflected from a pit and from its surrounding land.

A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The spiral begins at the center of the disc and proceeds outwards to the edge, which allows the different size formats available. To grasp the scale of the pits and land of a CD, if the disc is enlarged to the size of a stadium, a pit would be approximately the size of a grain of sand. The spacing between the tracks is 1.6 μm.

(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 long. The information on a standard CD is encoded as a spiral track of pits moulded into the top of the polycarbonate layer. There is a 15 mm hole in the centre of the disc, usually used by some form of clamp or clip device within the player to hold it in place and allow it to be rotated by a motor. Some irregularly shaped discs will work with tray loading CD drives if they include a circular ridge on their underside which centers them on the part of the tray designed to hold 80 mm CDs, assuming the tray has such a feature.

Irregularly shaped, non rotationally symmetric discs with an offset centre of mass may also cause damaging vibration if played in computer CD drives, which can operate at a much higher rotational velocity than stand-alone audio CD players. Examples include Business Card CDs in the shape of a rectangular card and CDs shaped like the map of a country etc, although such discs are not always compatible with all CD players — they will work with any machine where the disc is inserted by manually clipping it onto the spindle (the mechanism used in virtually all portable CD players), but may not necessarily be inserted into drives which load the disc from a tray, or pull it into a slot. Other unique shapes and smaller form factors have also been sold or given away as promotional items. Each such "miniCD" or "Maxi CD" can hold 21 minutes of music, or 180 MB of data (this form factor has also been called "CD3", since it is about three inches across).

Japan), much like the old vinyl single. 80 mm discs are also available, a format which is mainly used for audio CD singles in some regions (e.g. Such a standard disc weighs 15 grams. By far the most common is 120 mm in diameter, with a 74-minute audio capacity and a 650 MB data or a 80-minute audio capacity and a 700 MB data (See storage capacity; this form factor has also erroneously been called "CD5" since it is 4 3/4 inches in diameter, about five inches across).

CDs are available in two sizes. Common printing methods for compact discs are silkscreening and offset printing. The lacquer can be printed with a label. Compact discs are made from a 1.2 mm thick disc of polycarbonate plastic coated with a much thinner layer of Super Purity Aluminium (or rarely, gold, used for its data longevity, such as in some limited-edition audiophile CDs) layer which is protected by a film of lacquer.

The CD and its later extensions have been extremely successful: in 2004 the annual worldwide sales of CD-Audio, CD-ROM, and CD-R reached about 30 billion discs. A user-recordable CD for data storage, CD-R, was introduced in the early 1990s, and it became the de facto standard for exchange and archiving of computer data and music. A CD can store around 640 megabytes of data. With this it was now possible to disseminate massive amounts (for the time) of computer data instead of digital sound.

Two years later, in 1985, the CD-ROM (read-only memory) was introduced. From its origins as a music format, Compact Disc has grown to encompass other applications. [2]. It spurred the sale of compact disc players like no other recording before it, helped to drive down the price of players, induced other acts and record labels to release more music on CD and firmly established the format in the mind of the average consumer.

One of the first all-digital rock recordings and the first by a major act, Brothers in Arms played to the strengths of the CD by offering more and longer tracks, running ten minutes longer than the album's concurrent LP and cassette releases. This "highbrow niche" status of the CD format changed dramatically in May, 1985, when UK rock band Dire Straits released the album Brothers in Arms. The far larger popular and rock music industries were slower to adopt the new format, especially in the huge consumer markets in Europe and the United States. The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities and its handling quality received particular praise.

This event is often seen as the "Big Bang" of the digital audio revolution. The Compact Disc reached the market in late 1982 in Asia and early the following year in other markets. According to Philips, the Compact Disc was thus "invented collectively by a large group of people working as a team."[1]. The Compact Disc Story, told by a former member of the taskforce, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter.

Philips also contributed the Eight-to-Fourteen Modulation, EFM, which offers both a large playing time and a high resilience against disc handling damage such as scratches and fingerprints; while Sony contributed the error-correction method, CIRC. Philips contributed the general manufacturing process, based on the video Laserdisc technology. After a year of experimentation and discussion, the taskforce produced the "Red Book", the Compact Disc standard. Prominent members of the task force were Kees Immink and Toshitada Doi.

In 1979 Philips and Sony decided to join forces, setting up a joint task force of engineers whose mission was to design the new digital audio disc. At the end of the 1970s, Philips, Sony, and other companies presented prototypes of digital audio discs. In the early 1970s, using video Laserdisc technology, Philips' researchers started experiments with "audio-only" optical discs, initially with wideband frequency modulation FM and later digitized PCM audio signals. .

Online services such as CDDB were developed to work around these shortcomings in the computer age. As a result, the original CD format has a number of limitations; no built-in track names or disc naming for example. Only later did the concept of an 'audio file' arise, and the generalising of this to any data file. The design of the CD was originally conceived as an evolution of the gramophone record, rather than primarily as a data storage medium.

Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM. They hold about 20 minutes of audio. The 80 mm discs are used as "CD-singles" or novelty "business-card CDs". The 120 mm discs can hold 74 minutes of audio, and versions holding 80, 90 or even 99 minutes have been introduced.

Standard compact discs have a diameter of 120 mm, though 80 mm versions exist in circular and "business-card" forms. An audio CD consists of several stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. A standard compact disc, often known as an "audio CD" to differentiate it from later variants, stores audio data in a format compliant with the red book standard. It is the standard playback format for commercial audio recordings today.

A compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. ISBN 895793008. Middleton, Wisconsin: A-R Editions. The Compact Disc Handbook.

Pohlmann (1992). Kenneth C. 458-465, May 1998 [4]. Kees Immink, The Compact Disc Story, AES Journal, pp.

AAD: analog tape recorder used during session recording and subsequent mixing and/or editing, digital tape recorder used during mastering (transcription). ADD: analog tape record used during session recording, digital tape recorder used during subsequent mixing and/or editing and during mastering (transcription). DDD: digital tape recorder used during session recording, mixing and/or editing, and mastering (transcription). 276 bytes: error correction.

8 bytes: null. 4 bytes: error detection. 2 048 bytes: user data. 4 bytes: sector ID.

12 bytes: sync. Outer radius program area: 58 mm. Inner radius program area: 25 mm. Disc thickness: 1.2 mm.

Disc diameter 120 mm. Track pitch: 1.6 μm. Scanning velocity: 1.2–1.4 m/s (constant linear velocity) - Equivalent to about 500 rpm at the inside of the disc, or about 200 rpm at the outside edge.