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Cd Writer

Cd writer

A CD recorder, CD writer or CD burner is a compact disc drive that can be used to produce discs readable in other CD-ROM drives and audio CD players. A DVD recorder produces DVD discs playable in stand-alone video players or DVD-ROM drives. They are generally used for small-scale archival or data exchange, being slower and more materially expensive than the moulding process used to mass-manufacture pressed discs. A recorder encodes (or burns) data onto a recordable CD-R, DVD-R or DVD+R disc (called a blank) by selectively heating parts of an organic dye layer in the disc with a laser in its write head. This changes the reflectivity of the dye, thereby creating marks that can be read as with the "pits" and "lands" on pressed discs. The process is permanent and the media can be written to only once. For rewriteable CD-RW, DVD-RW and DVD+RW media, the laser is used to melt a crystalline metal alloy in the recording layer of the disc. Depending on the amount of power applied, the substance may be allowed to melt back into crystalline form or left in an amorphous form, enabling marks of varying reflectivity to be created. Most rewriteable media is rated by manufacturers at up to 1000 write/erase cycles. The competing DVD+R and DVD-R disc formats use very similar dye-based media, but differ mainly in the way timing hints for the write head are laid out on the disc surface. This is also the case with DVD+RW and DVD-RW. Most internal CD recorders for personal computers, server systems and workstations are designed to fit in a standard 5.25" drive bay and connect to their host via an ATA, SATA or SCSI bus. External CD recorders usually have USB, FireWire or SCSI interfaces. Some portable versions for laptop use power themselves off batteries or off their interface bus. SCSI recorders are less common and tend to be more expensive because of the cost of their interface chipsets and more complex SCSI connectors.

Compatibility

- Some types of CD-R media with less-reflective dyes may cause problems. Phthalocyanine-based discs are said to work best.
- May not work in non MultiRead-compliant drives.
- [http://www2.osta.org/osta/html/cddvd/intro.html May not work] in some early-model DVD-ROM drives.
- A large-scale [http://www.cdrinfo.com/Sections/Reviews/Specific.aspx?ArticleId=7664 compatibility test] conducted by cdrinfo.com in July 2003 found DVD-R discs playable by 96.74%, DVD+R by 87.32%, DVD-RW by 87.68% and DVD+RW by 86.96% of consumer DVD players and DVD-ROM drives.

Performance

Early-model recorders were CLV (constant linear velocity) drives. The recording speed on such drives was rated in multiples of 150 KiB/s; a 4X drive, for instance, would write steadily at around 600 KiB/s. The transfer rate was kept constant by having the spindle motor in the drive run about 2.5 times as fast when recording at the inner rim of the disc as on the outer rim. There are mechanical limits on the maximum angular velocity at which discs can be spun: at 25000 RPM and beyond, the tensile stress on the disc can expand small manufacturing defects in the disc polycarbonate and then cause the disc to warp and shatter. To keep the rotational speed of the disc safely low, more recent high-speed recorders tend to use the Z-CLV (zoned constant linear velocity) scheme. This divides the disc into stepped zones, each of which has its own constant linear velocity. A Z-CLV recorder rated at "52X", for example, would write at 20X on the innermost zone and then progressively step up to 52X at the outer rim. In the late 1990s, buffer overruns became a very common problem as high-speed CD recorders began to appear in home and office computers, which—for a variety of reasons—often could not muster the I/O performance to produce a data stream to keep the recorder steadily fed. The recorder, should it run short, would be forced to halt the recording process, leaving a truncated track that often renders the disc useless. In response, manufacturers of CD recorders began shipping drives with "buffer overrun protection" (under various trade names, such as Sanyo's "BURN-Proof", Ricoh's "JustLink" and Yamaha's "Lossless Link"); these can suspend and resume the recording process in such a way that the gap the stoppage produces can be dealt with by the error-correcting logic built into CD players and CD-ROM drives. The DVD+R and DVD+RW disc formats were designed with discontinuous recording in mind because they were expected to be widely used in digital video recorders. Many such DVRs used variable-rate video compression schemes which required them to record in short bursts; some allowed simultaneous playback and recording by alternating quickly between recording to the tail of the disc whilst reading from elsewhere.

External links

- [http://www.osta.org/technology/cdqa.htm Understanding CD-R & CD-RW]
- [http://www.pcnineoneone.com/howto/cdburnadv1.html Guide to CD Writing and writing standards]
- [http://www.cdrfaq.org CD-Recordable FAQ]
- [http://www.cdfreaks.com CD-Recordable News and Articles] Category:CD Category:120 mm discs Category:Audio storage Category:Video storage

Compact disc

A compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. It is the standard playback format for commercial audio recordings today. 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. An audio CD consists of several stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard compact discs have a diameter of 120 mm, though 80-mm versions exist in circular and "business-card" forms. The 120-mm discs can hold 74 minutes of audio, and versions holding 80 or even 90 minutes have been introduced. The 80-mm discs are used as "CD-singles" or novelty "business-card CDs". They hold about 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM.

History

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. At the end of the 70s, Philips, Sony, and other companies presented prototypes of digital audio discs. In 1979 Philips and Sony decided to join forces, setting up a joint taskforce of engineers whose mission was to design the new digital audio disc. Prominent members of the taskforce were Kees Immink and Toshitada Doi. After a year of experimentation and discussion, the taskforce produced the "Red Book", the Compact Disc standard. Philips contributed the general manufacturing process, based on the video Laserdisc technology. 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. The [http://www.exp-math.uni-essen.de/~immink/pdf/cdstory.pdf 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. According to Philips, the Compact Disc was thus "invented collectively by a large group of people working as a team."[http://www.research.philips.com/newscenter/dossier/optrec/index.html] The Compact Disc reached the market in late 1982 in Asia and early the following year in other markets. This event is often seen as the "Big Bang" of the digital audio revolution. The new audio disc was enthusiastically received and its handling quality received particular praise. From its origins as a music format, Compact Disc has grown to encompass other applications. Two years later, in 1985, the CD-ROM (read-only memory) was introduced. With this it was now possible to disseminate massive amounts of computer data instead of digital sound. 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. 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.

Physical details

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 lacquer can be printed with a label. Common printing methods for compact discs are silkscreening and offset printing. CDs are available in two sizes. By far the most common is 120 mm in diameter, with a 74-minute audio capacity and a 650-MB data (See storage capacity; this form factor has also erroneously been called "CD5" since it is about five inches across). Such a standard disc weighs 15 grams. They are also available as 80-mm discs, a format which is mainly used for audio CD singles in some regions (e.g. Japan), much like the old vinyl single. 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). Other unique shapes and smaller form factors have also been sold or given away as promotional items. Examples include Business Card CDs in the shape of a rectangular card and CDs shaped like the map of a country etc. There is 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. The information on a standard CD is encoded as a spiral track of pits moulded into the top of the polycarbonate layer (The areas between pits are known as lands). Each pit is approximately 125 nm deep by 500 nm wide, and varies from 850 nm to 3.5 μm long. The spacing between the tracks is 1.6 μm. 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 spiral begins at the center of the disc and proceeds outwards to the edge, which allows the different size formats available. A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The difference in height between pits and lands is one quarter of the wavelength of the laser light, leading to a half-wavelength phase difference between the light reflected from a pit and from its surrounding land. The destructive interference thus reduces the intensity of the reflected light compared to when the laser is focused on just a land. By measuring this intensity with a photodiode, one is able to read the data from the disc. The pits and lands themselves do not represent the zeroes and ones of binary data. Instead a change from pit to land or land to pit indicates a one, while no change indicates a zero. 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. 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. Consequently, discs are much easier to ruin by scratching their label side, whereas clear-side scratches can be repaired by refilling them with plastic of similar index of refraction.

Audio format

The format of the audio disc, known as the "Red Book"/Sony standard, was laid out by Sony and Philips in 1981. 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. 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. Reed-Solomon error correction allows the CD to be scratched to a certain degree and still be played back. 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. 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. This technology could store six samples (three samples per each stereo channel) in a single horizontal line. A standard NTSC video signal has 245 usable lines per field, and 59.94 fields/s, which works out at 44,056 samples/s. Similarly PAL has 294 lines and 50 fields, which gives 44,100 samples/s. This system could either store 14-bit samples with some error correction, or 16-bit samples with almost no error correction. 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. The Sony PCM-1610 and PCM-1630 are well known examples of PCM adaptors used in conjunction with the Sony U-matic VCR.

Storage capacity

The main parameters of the CD (taken from the September 1983 issue of the compact disc specification) are as follows:
- 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.
- Track pitch: 1.6 μm.
- Disc diameter 120 mm.
- Disc thickness: 1.2 mm.
- Inner radius program area: 25 mm.
- Outer radius program area: 58 mm. The program area is 86.05 cm², so that the length of the recordable spiral is 86.05/1.6 = 5.38 km. 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. If the disc diameter were 115 mm, the maximum playing time would have been 68 minutes, i.e., six minutes less. A disc with data appearing slightly more densely is allowable. 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. This is the limit for most conventional audio CDs today. 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. However, these discs can cause problems in playback when the end of the disc is reached. 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. CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. 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.

Data structure

The smallest entity in the CD audio format is called a frame. A frame can accommodate six complete 16-bit stereo samples, i.e. 2×2×6 = 24 bytes. Data in a CD-ROM are organized in both frames and sectors. A CD-ROM sector contains 98 frames, and holds 98×24 = 2352 bytes. 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. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed-Solomon error correction. Note that the CIRC error correction system used in the CD audio format has two interleaved layers. 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. In a Mode-2 CD-ROM, which is mostly used for video files, there are 2336 user-available bytes per sector. The net byte rate of a Mode-1 CD-ROM is 44.1k×2048/(6×98) = 153.6 kbyte/s. The playing time is 74 minutes, or 4440 seconds, so that the net capacity of a Mode-1 CD-ROM is 682 Mbyte.

Subcode

Besides digital audio, a CD contains digital data called "subcode", which is multiplexed with the digital audio. The data in a CD are arranged in frames. 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. The eight bits of a subcode byte are available for control and display. The eight bits are used as eight different subcoding channels, and given letters designating their usage: P, Q, …, W. Thus each channel has a bit rate of 7.35 (=44.1/6) kbit/s. In each sector there are 2352 bytes (24×98) of audio content data and 96 bytes of subchannel data. The 96 bytes of subchannel information in each sector contain four packets of 24 bytes apiece: 1 byte for command, 1 byte for instruction, 2 bytes for parityQ, 16 bytes for data, and 4 bytes parityP. Each of the 96 subchannel data bytes can be thought of as being divided into eight bits. Each of these bits corresponds to a separate stream of information. These streams are called "channels", and are labeled starting with the letter P, like so: Channel P is a simple pause/music flag, which can be used for low-cost search systems. Quite a few players ignore it in favor of the Q Channel. Channel Q is used for control purposes of more sophisticated players. It contains positioning information, the Media Catalog Number (MCN), and International Standard Recording Code (ISRC). 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: ;Data: This track contains Data (rather than audio). Can be used for muting in audio CD players. ;Copy Flag: Used by the Serial Copy Management System to indicate permission to digitally copy the track. ;Four Channel Audio: The track uses four channel audio. This is very rarely used on Compact Discs. ;Pre-Emphasis: The audio track was recorded with pre-emphasis. Used very rarely on Compact Discs. Channels R…W are unused by Red-Book compliant CDs, and have been used for extensions to the standard.

CD-Text

CD-Text is an extension of the Red Book standard for audio CDs. It allows for storage of additional information (e.g. album name, song name, and artist) on a standards-compliant audio CD. The information is stored in the lead-in area of the CD (there is roughly five kilobytes space there), or in the Subchannels R to W on the disc, which are not used on Red-Book compliant CDs. About 31 megabytes of information can be stored there. The text is stored in a format usable by the Interactive Text Transmission System (ITTS). ITTS is also used by Digital Audio Broadcasting or the MiniDisc. Note that other extensions such as CD+G also use those subchannels to store graphics in.

The AAD, ADD, DDD code for audio CDs

Many CDs, especially classical music, but also many popular recordings (especially on early CDs), come with a three letter code printed on the back, where "A" stands for analog and "D" stands for digital. 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). As a result, almost all early CDs are "AAD" (analog recording and mixing, digital transfer to CD). Often this code was accompanied by a short description such as "Full Digital Recording" for DDD and "Digitally Mixed Analog Recording" for ADD. Although experimental recordings exist from the 1960s, digital recording of classical and jazz music began to be made commercially in the early 1970s, pioneered by Japanese companies such as Denon; 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. In most such cases, there was no mixing stage involved; a stereo digital recording was made and used unaltered as the master tape for subsequent commercial release. These, and other subsequent unmixed digital recordings are still described as DDD, as the technology involved is purely digital. (Likewise, unmixed analog recordings are usually described as ADD, to denote a single generation of analog recording). The first digitally recorded (DDD) popular music album was Bop Till You Drop by Ry Cooder, recorded in late 1978; it was unmixed, being recorded straight to a two-track 3M digital recorder in the studio. Many other top recording artists, such as Stevie Wonder, were early adherents of digital recording; Wonder adopted the technology in early 1979 for Journey Through the Secret Life of Plants and all subsequent recordings. 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; however, he used digital mixing to eliminate the distortion and noise that an analog master tape would introduce (thus ADD). An early example of an analog recording that was digitally mixed is Tusk by Fleetwood Mac, from 1979. 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. Two examples from 1982 are Signals by Rush, and The Nightfly by Donald Fagen. 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. A notable example is Herb Alpert's Rise album from 1979. When it started making LPs and cassettes, the originally CD-only label Ryko extended this system to the other media, so that a digital recording on an LP would be DDA, and so forth.

CD-ROM

For its first few years of existence, the compact disc was purely an audio format. 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.

Recordability

Injection moulding is used to mass produce compact discs. 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. This dye is then etched, leaving the data track. It is then plated to make a positive version of the CD. Polycarbonate is liquified and injected into the mold cavity where the stamper transfers the pattern of pits and lands to the polycarbonate disc. The disc is then metallized with aluminum and lacquer coated. Recordable compact discs are injection molded with a "blank" data spiral. A photosensitive dye is then applied, and then the discs are metallized and lacquer coated. 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. CD-R recordings are permanent. The resulting discs can be read by most CD-ROM drives and played in most audio CD players. 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 chemical properties of the alloy and hence change its reflectivity. 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.

Copy protection

The Red Book audio specification does not include any copy protection mechanism. 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. An error-correcting code is included with Red Book audio to deal with small scratches or defects on the disc media. Where error correction fails on larger defects, audio CD players are expected to apply interpolation algorithms to conceal the loss of audio data. Starting in early 2002, attempts were made by record companies to market "copy-protected" compact discs. 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). 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. 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. 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. It also seems likely that Philips' new models of CD recorders will be designed to be able to record from these "protected" discs. However, there has been great public outcry over copy-protected discs because many see it as a threat to fair use. Other systems developed are Macrovision CDS-200 and Mediamax CD-3. In any case, even if a disc cannot be directly ripped, it can still be played in audio mode, and the audio thence captured. Any loss of sound quality caused by this method is generally considered negligible. This is commonly referred to as the analog hole.

Non-standard CD behaviors

Some commercially released audio discs have a "secret" bonus track. These may be an extension of the last audio track or a separate track hidden from the disc's table of contents. Either way, the hidden portion is heard when the disc is played to the end. Other discs hide the extra material at the beginning of the disc. On most discs, the location of the first track listed in the table of contents immediately follows the table of contents itself. In this case, the hidden track is an unlisted track sandwiched between the two. To hear the hidden track, the listener must usually "rewind" the player past the beginning of the first listed track. Not all players allow this.

Name

Notwithstanding the variability of general usage between "disk" and "disc" [http://www.bartleby.com/61/16/C0521600.html], the customary spelling is "compact disc", rather than "compact disk". This may be in large degree due to its status as a Philips trademark under that spelling.

References

- Kees Immink, The Compact Disc Story, AES Journal, pp. 458-465, May 1998 [http://www.exp-math.uni-essen.de/~immink/pdf/cdstory.pdf].
- Kenneth C. Pohlmann (1992). The Compact Disc Handbook. Middleton, Wisconsin: A-R Editions. ISBN 895793008.

CD ROM

The CD-ROM (an abbreviation for "Compact Disc Read-Only Memory") is a non-volatile optical data storage medium using the same physical format as audio CDs, readable by a computer with a CD-ROM drive. A CD-ROM is a flat, metallized plastic disc with digital information encoded on it in a spiral from the center to the outside edge. The CD-ROM Yellow Book standard was established in 1985 by Sony and Philips. Microsoft and Apple Computer were early enthusiasts and promoters of CD-ROMs. John Sculley, CEO of Apple at the time, said as early as 1987 that the CD-ROM would revolutionize the use of personal computers. personal computer CD-ROM reading devices are a standard component of most modern personal computers. In general, audio CDs are distinct from CD-ROMs, and CD players intended for listening to audio cannot make sense of the data on a CD-ROM; though personal computers can generally read audio CDs. It is possible to produce composite CDs containing both data and audio with the latter capable of being played on a CD player, whilst data or perhaps video can be viewed on a computer. These are called Enhanced CDs.

Manufacture

CD-ROMs are always pressed (mass-produced), whereas CD-Rs are recorded. There exist devices to 'burn', or record, multiple discs at once from a single source. The contents of a CD-R may be in logical CD-ROM format (Yellow Book) but the disc itself is physically a CD-R (Orange Book). Source: Dana J. Parker, author of The CD-Recordable Handbook. [http://www.amazon.com/exec/obidos/tg/detail/-/0910965188/qid=1111091690/sr=1-2/ref=sr_1_2/103-7169860-7230214?v=glance&s=books]

Capacity

The standard CD-ROM can hold 650-700 megabytes of data. The CD-ROM is popular for distribution of software, especially multimedia applications, and large databases. A CD weighs under an ounce. To put the CD-ROM's storage capacity into context, the average novel contains 60,000 words. Assume that average word length is 10 letters - in fact it is less than 10 - and that each letter occupies one byte. A novel therefore might occupy 600,000 bytes. One CD can therefore contain over 1,000 novels. If each novel occupies half an inch of bookshelf space, then one CD can contain the equivalent of about 14 yards (~13 metre) of bookshelf. However textual data can be compressed by more than a factor of ten, using computer compression algorithms (often known as 'zipping'), so a CD-ROM can accommodate at least 100 yards of bookshelf space. In comparison a DVD typically contains 4.7 GB of data or more, depending upon its type. Dual layer DVD+R discs, for example, contain 8.5GB of data for a normal sized (12 cm) disc.

CD-ROM drives

DVD CD-ROMs are read using CD-ROM drives and written with CD recorders (often referred to as "burners"). CD-ROM drives—now almost-universal on personal computers—may be connected to the computer via an IDE (ATA) interface, a SCSI interface or a proprietary interface, such as the Panasonic CD interface. Most CD-ROM drives can also play audio CDs and Video CDs with the right software. CD-ROM drives are rated with a speed factor relative to music CDs: 1x or 1-speed which gives a data transfer rate of 150 kilobytes per second in the most common data format. For example, an 8x CD-ROM data transfer rate would be 1.2 megabytes per second. Above 12x speed, there are problems with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 20x but due to the nature of CAV the actual throughput increase over 12x is less than 20/12. 20x was thought to be the maximum speed due to mechanical constraints until February 1998, when Samsung Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a ball bearing system to balance the spinning disc in the drive to reduce vibration and noise. As of 2004, the fastest transfer rate commonly available is about 52x or 7.62 megabytes per second, though this is only when reading information from the outer parts of a disc. Future speed increases based simply upon spinning the disc faster are particularly limited by the strength of polycarbonate plastic used in CD manufacturing. Speed improvements can however still be obtained by the use of multiple laser pickups as demonstrated by the Kenwood TrueX 72x which uses seven laser beams and a rotation speed of approximately 10x. CD-Recordable drives are often sold with three different speed ratings, one speed for write-once operations, one for re-write operations, and one for read-only operations. The speeds are typically listed in that order; ie a 12x/10x/32x CD drive can, CPU and media-permitting, write to CD-R disks at 12x speed (1.76 megabytes/s), write to CD-RW discs at 10x speed (1.46 megabytes/s), and read from CD discs at 32x speed (4.69 megabytes/s). The 1x speed rating for CDs (150 kilobytes/s) is not to be confused with the 1x speed rating for DVDs (1.32 megabytes/s). Some of the initial versions of CD Drives had a mechanism different from the tray or slot loaders of modern day drives. They could read CDs only when they were inserted in special cartridges. The "CD Caddy" resembled the floppy disk because of its protective casing. It, however, never caught on.

Copyright Issues

There has been a move by the recording industry to make audio CDs (CDDAs, Red Book CDs) unplayable on computer CD-ROM drives, to prevent copying of the music. This is done by intentionally introducing errors onto the disc that audio players can automatically compensate for, but confuse CD-ROM drives. Consumer rights advocates are as of October 2001 pushing to require warning labels on compact discs that do not conform to the official Compact Disc Digital Audio standard (often called the Red Book) to inform consumers of which discs do not permit full fair use of their content. Manufacturers of CD writers (CD-R or CD-RW) are encouraged by the music industry to ensure that every drive they produce has a unique identifier, which will be encoded by the drive on every disc that it records: the RID or Recorder Identification Code. This is a counterpart to the SID - the Source Identification Code, an eight character code beginning with "IFPI" that is usually stamped on discs produced by CD recording plants.

Data Formats

There are several formats used for CD-ROM data: the Rainbow Books, which include the Green Book, White Book and Yellow Book CD-ROM. ISO 9660 defines the standard file system of a CD-ROM, although it is due to be replaced by ISO 13490. UDF format is used on user-writable CD-R and CD-RW discs that are intended to be extended or overwritten. The bootable CD specification, to make a CD emulate a hard disk or floppy, is called El Torito (apparently named after the restaurant chain). Informative CD-ROMs may contain links to webpages with additional information. To keep them up to date these are sometimes indirect: they link to webpages maintained by the producer of the CD-ROM which contain the links to external webpages.

References

External links

- [http://computer.howstuffworks.com/cd.htm How CDs Work from HowStuffWorks.com]
- [http://www.cdrfaq.org Andy McFadden's CD-Recordable FAQ]
- [http://www.osta.org/technology/cdqa.htm Understanding CD-R & CD-RW] by Hugh Bennett
- [http://www.pcdoctor-guide.com/wordpress/?p=1396Inside a CD-ROM drive from The PC Doctor] Category:120 mm discs Category:Computer storage media Category:Audio storage ja:CD-ROM

CD-R

right A CD-R (Compact Disc-Recordable) is variation of the Compact Disc digital audio disc invented by Philips and Sony. The CD-R retains all the abilities of the CD standard but adds the functionality of being able to store either music or data.

History

The CD-R, originally named CD Write-Once (WO), specification was first published in 1988 by Philips and Sony in the 'Orange Book'. The Orange Book consists of several parts, furnishing details of the CD-WO, CD-MO (Magneto-Optic), and CD-RW (ReWritable). The latest editions have abandoned the use of the term "CD-WO" in favor of "CD-R". Written CD-Rs and CD-RWs are fully compatible with the Audio CD (Red Book) and CD-ROM (Yellow Book) standards. They use Eight-to-Fourteen Modulation, EFM, CIRC error correction plus the third error correction layer defined for CD-ROM. The first CD-Rs were produced in 1994. Compatibility of CD-R and conventional read-only discs, CD and CD-ROM, is a miraculous achievement which was made possible by the dye materials developed by Taiyo Yuden.

Physical characteristics

A standard CD-R is a 1.2 mm thick disc made of polycarbonate with a 120 mm or 80 mm diameter. It has a storage capacity of 74 minutes of audio or 650 MB of data. Non-standard CD-Rs are available with capacities of 79 minutes, 59 seconds and 74 frames /736,966,656 bytes (702 MB), which they achieve by slightly exceeding the tolerances specified in the Orange Book CD-R/CD-RW standards. Most CD-Rs on the market are of the latter capacity. There are also 90 minute/790 MB and 99 minute/870 MB discs, though they are rare. The polycarbonate disc contains a spiral groove to guide the laser beam upon writing and reading information. The disc is coated on the side with the spiral groove with a very thin layer of organic dye and subsequently with a thin, reflecting layer of silver, a silver alloy or gold. Finally, a protective coating of a photo-polymerizable lacquer is applied on top of the metal reflector and cured with UV-light. A blank CD-R is not "empty", it has a pregroove with a wobble (the ATIP), which helps the writing laser stay on track and is used to ensure the data is written to the disc at a constant rate. As well as providing timing information, the ATIP (absolute time in pregroove) is also a data track containing information about the CD-R manufacturer, the dye used and media information (disc length etc). The pregroove is not destroyed when the data is written to the CD-R, many copy protections use this to easily distinguish a copy from the original CD. Among the first CD-R manufacturers were the companies Taiyo Yuden, Kodak, Maxell, and TDK. Since then, the CD-R was further improved to allow writing speeds as fast as 52x (as of 2004) relative to the first 1x CD-Rs. The improvements were mainly due to optimisation of special dye compositions for CD-R, groove geometry, and the dye coating process. Low-speed burning at 1x is still used for special "audio CD-Rs", since CD-R audio recorders were standardized to this recording speed. There are three basic formulations of dye used in CD-Rs: #Cyanine dyes were the earliest ones developed, and their formulation is patented by Taiyo Yuden. Cyanine dyes are mostly green or light blue in color, and are chemically unstable. This makes cyanine discs unsuitable for archival use; they can fade and become unreadable in a few years. Many manufacturers use proprietary chemical additives to make more stable cyanine discs. #Azo dye CD-Rs are dark blue in color, and their formulation is patented by Mitsubishi Chemicals. Unlike cyanine, azo dyes are chemically stable, and typically rated with a lifetime of decades. #Phthalocyanine dye CD-Rs are usually silver, gold or light green. The patents on pthalocyanine CD-Rs are held by Mitsui and Ciba Specialty Chemicals. These are also chemically stable, and often given a rated lifetime of hundreds of years. Although the CD-R was initially developed in Japan, most of the production of CD-Rs had moved to Taiwan by 1998. Taiwanese manufacturers supplied more than 70% of the worldwide production volume of 10.5 billion CD-Rs in 2003. Unfortunately, many manufacturers add additional coloring to disguise their cyanine CD-Rs, so you cannot determine the formulation of a disc based purely on its color. Similarly, a gold reflective layer does not guarantee use of phthalocyanine dye.

Writing methods

A CD recorder is a special type of CD-ROM drive used to write onto blank CD-R media. A laser is used to "burn" small pits into the dye so that the disc can later be read by the laser in a CD-ROM drive or CD player. The laser used to write CD-Rs is an infrared laser which emits laser radiation at a wavelength of 780 nm. The reflectivity in the pit area is different (lower) than for the unchanged dye area, because the refractive index of the dye is lowered upon "burning" a pit. Upon reading back the stored information, the laser operates at a low enough power not to "burn" the dye and an optical pick-up records the changes in the intensity of the reflected laser radiation when scanning along the groove and over the pits. The change of the intensity of the reflected laser radiation is transformed into an electrical signal, from which the digital information is recovered ("decoded"). The decomposition of the dye in the pit area through the heat of the laser is irreversible (permanent). Therefore, once a section of a CD-R is written, it cannot be erased or rewritten, unlike a CD-RW. A CD-R can be recorded in multiple sessions. A CD recorder can write to a CD-R using several methods including: #Disc At Once - the whole CD-R is written in one session with no gaps and the disc is "closed" meaning no more data can be added and the CD-R effectively becomes a standard read-only CD. With no gaps between the tracks the Disc At Once format is useful for "live" audio recordings. #Track At Once - data is written to the CD-R one track at a time but the CD is left "open" for further recording at a later stage. It also allows data and audio to reside on the same CD-R. #Packet Writing - used to record data to a CD-R in packets allowing extra information to be appended to a disc at a later time or information on the disc can be made "invisible". In this way CD-R can emulate CD-RW however each time information on the disc is altered more data has to be written to the disc. There can be compatibility issues with this format and some CD drives. A rough estimation of the amount of data on a CD-R can be gained by inspecting the playback side of the disc. A visible variation in the surface can be observed. CD-Rs are written from the center of the disc outwards.

Optimal storage conditions and expected lifespan

At present, stated CD-R lifetimes are only estimates based on accelerated aging tests as the technology has not been in existence long enough to verify the upper range. With proper care it is thought that CD-Rs should be readable one thousand times or more and have a shelf life of several hundred years. Unfortunately, some common practices can reduce shelf life to only one or two years. Therefore, it is important to handle and store CD-Rs properly if you wish to read them more than a year or so later. Recommended care and storage practices for CD-Rs include:
- Store vertically in jewel cases or slim-line cases, one disc to a spindle. Archival cases use a ridged ring which grip the disc and prevent the recording surface from touching the surface of the case.
- Avoid bending the disc. To remove a CD-R from a jewel case, press down on the hub while gently gripping the edges of the disc; you should be able to simply lift the disk out of the case.
- Always hold a CD-R by lightly gripping the edges of the disc. Try to avoid getting fingperprints on the data side of the disc.
- Store in a cool, dry place. Optimal temperature range is 5-20°C (41-68°F). Optimal relative humidity range is 30-50%. These values should not be allowed to change rapidly.
- Avoid direct sunlight. Sunlight can heat a jewel case and indirectly thermally stress the disc itself. Direct UV radiation on either side of the disc itself can degrade the dye layer in a CD-R. On the other hand, X-ray radiation, from airport screening for example, and magnetism should not affect a CD-R.
- If possible, use only a felt-tip water-based marker to mark the label side of the CD-R. The best place to label a CD-R is the clear inner part near the center. Alchohol-based markers are thought to be less harmful than xylene or toluene-based markers. Typical permanent markers are xylene or toluene based and should never be used to label optical media. Many vendors sell marking pens which are safe to use to label optical storage media.
- Paper labels should be applied to the outside of the jewel case, not to the label side of the CD-R itself. Over time, solvents in the paper, adhesives and inks can all degrade the disc. Labels applied unevenly to the disc can also cause the CD-R to wobble in high speed players and render them unusable.
- Avoid scratching either side of a CD-R. Perhaps counterintuitively even minor scratches on the label side can damage a disc. Because CD-Rs use error-correcting codes, minor scratches on the data side should not render the disc unreadable, unless there are many of them close together. Deep scratches on the data side can interfere with the focus of the laser and render a disc unreadable. Scratches from rim to center are less harmful than concentric circular scratches. Writing on the label side of CD-R with a ballpoint pen can destroy it.
- Whilst not water proof, CD-Rs are not greatly affected by exposure water unless they have inkjet printing on the label side. Water will cause any inkjet printing to run unless it is protected by an outer layer.

Cleaning CD-Rs

As a general rule only clean a CD-R if the playback is affected. The error correction of CD-R can effectively read through fingerprints as well as a highly scratched information surface. Excess dust can be removed from the information surface by very lightly wiping the information side with a very soft cloth (such as a reading glasses cleaning cloth) from the centre of the disc in an outwards direction. Never wipe the information surface of any type of CD in in circular motion around the centre as this may create scratches in the same direction as the information and potentially cause data loss. Fingerprints or stubborn dust can be removed from the information surface by wiping it with a cloth dampened with alcohol (methylated spirits or isopropyl alcohol) and again wiping from the centre outwards, with a very soft cloth. Never use acetone, nailpolish remover, kerosene, petrol (gasoline) or any other type of petroleum-based solvent to clean a CD-R. Use of petroleum based solvents will damage the polycarbonate surface and the CD-R will become unreadable. Use only alcohol based products.

Readability in CD drives

There was some incompatibility with CD-Rs and older CD-ROM drives. This was primarily due to the lower reflectivity of the CD-R disc. In general, CD-ROM drives marked as 8x or greater will read CD-R discs. Some DVD players will not read CD-Rs because of this change in reflectivity as well.

External links

- [http://www.osta.org/technology/cdqa.htm Understanding CD-R & CD-RW] by Hugh Bennett
- [http://www.cdrfaq.org/ The CD-R FAQ]
- [http://www.osta.org/specs/pdf/opc.pdf Running Optimum Power Control: Data Integrity in CD-Recording] by Hugh Bennett
- [http://www.clir.org/pubs/reports/pub121/contents.html Care and Handling of CDs and DVDs: A Guide for Librarians and Archivists], by Fred R. Byers; issued by the Council on Library and Information Resources (CLIR) and NIST
- [http://www.chipchapin.com/CDMedia/cdr3.php3 Pregroove and timing on a CD-R] Category:CD Category:120 mm discs Category:Audio storage Category:Video storage ja:CD-R

DVD-R

DVD-R discs]] A DVD-Recordable or DVD-R (pronounced "DVD Are" or "DVD Dash Are") is an optical disc with a larger storage capacity than a CD-R, typically 4.7 GB (4.38 GiB) instead of 700 MiB, although the capacity of the original standard was 3.95 GB. Pioneer has also developed a 8.54 GB dual layer version, which appeared on the market in 2005. A DVD-R can be written to only once, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple times. The DVD-R format was developed by Pioneer in autumn of 1997. It is supported by most DVD players, and is approved by the DVD Forum. A competing format is DVD+R (also DVD+RW for the rewritables). Hybrid drives that handle both formats are often labeled DVD±R and Super Multi (which includes DVD-RAM support) and are very popular. The larger storage capacity of a DVD-R compared to a CD-R is achieved through smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer (see CD-R) a red laser beam with a wavelength of 650 nm (for general use recordable DVD) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength, compared to CD-R, DVD-R and DVD+R use different dyes to properly absorb this wavelength. DVD-R discs are composed of two 0.6 mm polycarbonate discs, bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver, silver alloy or gold reflector. The other one (for single-sided discs) is an ungrooved "dummy" disc to assure mechanical stability of the sandwich structure, and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm. Double-sided discs have two grooved, recordable disc sides, and require the user to flip the disc to access the other side. Compared to a CD's 1.2 mm of polycarbonate, a DVD's laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size, which is key for writing smaller pits. In a DVD-R, the addressing (the determination of location of the laser beam on the disc) is done with additional pits and lands (called land pre-pits) in the areas between the grooves. The groove on a DVD-R disc has a constant wobble frequency used for motor control etc.

Capacities

A DVD advertised as 4.7 GB may hold less than that because manufacturers quote the capacity of a writable DVD disc in decimal rather than binary notation. This can be confusing. While a 4.7 GB DVD technically can store 4.7 billion "base 10" bytes [4,700,000,000 bytes ÷ 1000 = 4,700,000 kB ÷ 1000 = 4,700 MB ÷ 1000 = 4.7 GB], in binary notation the same disc has a capacity of roughly 4.38 GiB [4,700,000,000 bytes ÷ 1024 = 4,589,844 KiB ÷ 1024 = 4,482.27 MiB ÷ 1024 = 4.38 GiB]. [http://www.osta.org/technology/dvdqa/dvdqa6.htm]

References

- Bennett, Hugh. "In DVD's Own Image: DVD-R Technology and Promise." EMedia Professional July 1998: 30+
- Bennett, Hugh. Understanding Recordable & Rewritable DVD. Cupertino: Optical Storage Technology Association, Apr. 2004. [http://www.osta.org/technology/dvdqa/]

External links

- [http://www.sharpened.net/helpcenter/answer.php?129 Difference between DVD-R and DVD+R formats]
- [http://www.osta.org/technology/dvdqa/ Understanding Recordable & Rewritable DVD] by Hugh Bennett
- [http://www.pioneer.co.jp Pioneer Corporation]
- [http://www.dvdforum.com DVD Forum]
- [http://www.cdfreaks.com/article/201 DVD-R Dual Layer First Look]
- [http://www.clir.org/pubs/reports/pub121/contents.html Care and Handling of CDs and DVDs], by Fred R. Byers Category:120 mm discs Category:DVD ja:DVD-R

DVD plus R

A DVD+R is a writable optical disc with 4.7 GB (4.38 GiB) of storage capacity (interpreted as

\approx 4.7\cdot10^9

, actually 2295104 sectors of 2048 bytes each). The format was developed by a coalition of corporations, known as the DVD+RW Alliance, in mid 2002. Since the DVD+R format is a competing format to the DVD-R format, which is developed by the DVD Forum, it has not been approved by the DVD Forum, which claims that the DVD+R format is not an official DVD format. In October of 2003, it was demonstrated that double layer technology could be used with a DVD+R disc to nearly double the capacity to 8.5 GB per disc. Manufacturers have incorporated this technology into commercial devices since mid-2004 (see DVD+R DL). Unlike DVD+RW discs, DVD+R discs can only be written to once. Because of this, DVD+R discs are suited to applications such as nonvolatile data storage, audio, or video. The DVD+R format is divergent from the DVD-R format. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular since there is not yet a single standard for recordable DVDs. There are a number of significant technical differences between the dash and plus formats, and although most consumers would not notice the difference, the plus format is considered by some to be better engineered. Like other plus media, it is possible to use bitsetting to increase the compatibility of DVD+R media. As of 2005, the market for recordable DVD technology shows little sign of settling down in favor of either the plus or dash formats, which is mostly the result of the increasing numbers of dual-format devices that can record to both formats; it has become very difficult to find new devices that can only record to one of the formats.

External links

- [http://www.dvdrw.com DVD+RW Alliance]
- [http://www.sharpened.net/helpcenter/answer.php?129 Difference between DVD-R and DVD+R formats]
- [http://www.osta.org/technology/dvdqa/ Understanding Recordable & Rewritable DVD]
- [http://www.dvdplusrw.org Unofficial DVD+RW Resource]
- [http://www.cdfreaks.com/article/113 Why DVD+R(W) is superior to DVD-R(W)] Category:120 mm discs Category:DVD Category:Audio storage Category:Video storage

CD-RW

Compact Disc ReWritable (CD-RW) is a rewritable optical disc format. Known as CD-Erasable (CD-E) during its development, CD-RW was introduced in 1997. While a prerecorded compact disc has its information permanently stamped into its polycarbonate plastic substrate, a CD-RW disc contains a phase-change alloy recording layer composed of silver, indium, antimony and tellurium. An infra-red laser beam is employed to selectively heat and melt the crystallized recording layer into an amorphous state or to anneal it at a lower temperature back to its crystalline state. The different reflectance of the resulting areas make them appear like the pits and lands of a prerecorded CD. A CD-RW recorder can rewrite 700 MiB of data to a CD-RW disc roughly 1000 times. CD-RW recorders can also write CD-R discs. Except for the ability to completely erase a disc, CD-RWs act very much like CD-Rs and are subject to the same restrictions; i.e., they can be extended, but not selectively overwritten, and writing sessions must be closed before they can be read in CD-ROM drive or players. The UDF 1.5 file system allows CD-RWs to be randomly rewritten, but limits disc storage capacity to roughly 530MB. Written CD-RW discs do not meet Red Book or Orange Book Part II standards for prerecorded or recordable CDs (e.g. reduced signal levels). Consequently, CD-RWs cannot be read in CD-ROM drives built prior to 1997. CD-R is considered a better technology for archival purposes as disc contents cannot be modified and manufacturers claim greater longevity. CD-RW discs need to be blanked before reuse. Different blanking methods can be used, including "full" blanking in which the entire surface of the disc is cleared, and "fast" blanking in which only meta-data areas are cleared: PMA, TOC and pregap, comprising a few percent of the disc. Fast blanking will obviously be much quicker, and is usually sufficient to allow rewriting the disc. Full blanking removes traces the former data for example for confidentiality.

References

- Bennett, Hugh. "CD-E: Call it Erasable, Call it Rewritable, but will it Fly?" CD-ROM Professional Sept. 1996: 28+
- Bennett, Hugh. Understanding CD-R & CD-RW. Cupertino: Optical Storage Technology Association, Jan. 2003.

External links

- [http://www.osta.org/technology/cdqa.htm Understanding CD-R & CD-RW] by Hugh Bennett
- [http://www.cdrfaq.org/ The CD-R FAQ]
- [http://gentoo-wiki.com/HOWTO_Packet_Writing_on_CD-RW HOWTO Packet Writing on CD-RW under Linux] Category:CD Category:120 mm discs Category:Audio storage Category:Video storage ja:CD-RW

DVD-RW

A DVD-RW is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. Unlike DVD-RAM, it is playable in about 75% of conventional DVD players. The primary advantage of DVD-RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc. According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement, making them comparable with the CD-RW standard. DVD-RW discs are commonly used for volatile data, such as backups or collections of files. They are also increasingly used for home DVD video recorders. Unlike DVD-R, the DVD-RW standard has always dictated a capacity of 4.7 GB. One competing rewritable format is DVD+RW. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular since there is not yet a single standard for recordable DVDs. The recording layer in DVD-RW and DVD+RW is not an organic dye, but a special metal alloy. The alloy can be switched back and forth between a crystalline phase and an amorphous phase, changing the reflectivity, depending on the power of the laser beam. Data can thus be written, erased and re-written.

External links

- [http://www.osta.org/technology/dvdqa/ Understanding Recordable & Rewritable DVD]
- [http://www.pioneer.co.jp Pioneer Corporation]
- [http://www.dvdforum.org DVD Forum] Category:120 mm discs Category:DVD

DVD plus RW

leftA DVD+RW is a rewritable optical disc with equal storage capacity to a DVD+R, typically 4.7 GB (interpreted as ≈ 4.7 · 10⁹, actually 2295104 sectors of 2048 bytes each). The format was developed by a coalition of corporations, known as the DVD+RW Alliance, in late 1997, although the standard was abandoned until 2001, when it was heavily revised and the capacity increased from 2.8 GB to 4.7 GB. Credit for developing the standard is often attributed unilaterally to Philips, one of the members of the DVD+RW Alliance. Although DVD+RW has not yet been approved by the DVD Forum, the format is too popular for manufacturers to ignore, and as such, DVD+RW discs are playable in 3/4 of today's DVD players. Unlike the DVD-RW format, DVD+RW was made a standard earlier than DVD+R. One competing rewritable format is DVD-RW. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular since there is not yet a single standard for recordable DVDs. DVD+RW discs can be rewritten about 1,000 times, making them comparable with the CD-RW standard. DVD+RW discs are commonly used for volatile data, such as backups or collections of files. However, they are not as widely used for home DVD video recorders as DVD-RW, primarily because they were originally designed for storage of data, rather than of video. Of late, a number of cheaper and "no-name" manufacturers have started releasing DVD recorders using the DVD+RW format rather than DVD-RW, leaving the branded manufacturers (except Philips of course) to fly the DVD-RW flag. For computer use, the DVD-R non-rewritable variant of DVD-RW is vastly more popular than DVD+R, and mail order or bulk pricing of DVD-R media is significantly cheaper than DVD+R. DVD+RW disks purportedly support a feature called "lossless linking" which is supposed to allow some amount of re-writing without requiring a full erasure of the disc.

External links

- [http://www.osta.org/technology/dvdqa/ Understanding Recordable & Rewritable DVD] by Hugh Bennett
- [http://www.dvdrw.com DVD+RW Alliance] Category:120 mm discs Category:DVD

Amorphous solid

An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. (Solids in which there is long-range atomic order are called crystalline solids.) Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous ceramic, many polymers (such as polystyrene) are amorphous, and even foods such as cotton candy are amorphous solids. Amorphous materials are commonly prepared by rapidly cooling molten material. The cooling reduces the mobility of material's molecules before they can pack into a more thermodynamically favorable crystaline state. Some materials, such as metals, are difficult to prepare in an amorphous state. Unless a material has a high melting temperature (as ceramics do) or a low crystallization energy (as polymers tend to), solidification must be done extremely rapidly. Amorphous solids can exist in two distinct states, the 'rubbery' state and the 'glassy' state. The temperature at which the transition between the glassy and rubbery states is called their glass transition temperature or T_g.

Glasses

In common parlance, the term glass refers to amorphous oxides, and especially silicates (compounds based on silicon and oxygen). To avoid confusion, other types of glass often are referred to with a modifier, such as the term metallic glass to refer to amorphous metallic alloys.

Metallic glass

Some amorphous metallic alloys can be prepared under special processing conditions (such as rapid solidification, thin-film deposition, or ion implantation), but the term "metallic glass" refers only to rapidly solidified materials. Even with special equipment, such rapid cooling is required that, for most metals, only a thin wire or ribbon can be made amorphous. This is enough for many magnetic applications, but thicker sections are required for most structural applications such as scalpel blades, golf clubs, and cases for consumer electronics. Recent efforts have made it possible to increase the maximum thickness of glassy castings, by finding alloys where kinetic barriers to crystallization are greater. Such alloy systems tend to have the following inter-related properties:
- Many different solid phases are present in the equilibrium solid, so that any potential crystal will find that most of the nearby atoms are of the wrong type to join in crystallization
- The composition is near a deep eutectic, so that low melting temperatures can be achieved without sacrificing the slow diffusion and high liquid viscosity seen in alloys with high-melting pure components
- Atoms with a wide variety of sizes are present, so that "wrong-sized" atoms interfere with the crystallization process by binding to atom clusters as they form. One such alloy is the commercial "Liquidmetal", which can be cast in amorphous sections up to an inch thick.

Other synthesis routes

Amorphous solids produced by other routes, such as ion implantation and thin-film deposition are, technically speaking, not glasses.

Damage

One way to produce a material without an ordered structure is to take a crystalline material and remove the order by damaging it. A practical, controllable way to do this is by firing ions into the material at high speed, so that collisions inside the material knock all atoms from their original positions. This technique is known as ion implantation, and only forms amorphous solids if the material is too cold for atoms to diffuse back to their original positions as the process continues.

Cold Deposition

Techniques such as sputtering and CVD can be used to deposit a thin film of material onto a surface. If the surface is kept cold, the atoms being deposited will not, on average, gain enough energy to diffuse along the surface until they find a place in an ordered crystal. For every deposition technique, there is a substrate temperature below which the deposited film will be amorphous. However, surface diffusion requires much less energy than diffusion through the bulk, so that these temperatures are often lower than those required to make amorphous films by ion implantation.

Toward a strict definition

It is difficult to make a distinction between truly amorphous solids and crystalline solids in which the size of the crystals is very small (less than two nanometres). Even amorphous materials have some short-range order among the atomic positions (over length scales of about one nanometre). Furthermore, in very small crystals a large fraction of the atoms are located at or near the surface of the crystal; relaxation of the surface and interfacial effects distort the atomic positions, decreasing the structural order. Even the most advanced structural characterization techniques, such as x-ray diffraction and transmission electron microscopy, have difficulty in distinguishing between amorphous and crystalline structures on these length scales. The transition from the liquid state to the glass, at a temperature below the equilibrium melting point of the material, is called the glass transition. From a practical point of view, the glass transition temperature is defined empirically as the temperature at which the viscosity of the liquid exceeds a certain value (commonly 10¹³ pascal-seconds). The transition temperature depends on cooling rate, with the glass transition occurring at higher temperatures for faster cooling rates. The precise nature of the glass transition is the subject of ongoing research. While it is clear that the glass transition is not a first-order thermodynamic transition (such as melting), there is debate as to whether it is a higher-order transition, or merely a kinetic effect. Glass is often referred to as a 'super-cooled' liquid: this amounts to an assertion that the glass transition is purely a kinetic, rather than a thermodynamic effect. One argument against speaking this way is the fact that many supercooled liquids flow (see pitch drop experiment) whereas glass does not (see special section in glass). Some examples of amorphous solids are glass, polystyrene, and the silicon in many thin film solar cells. Category:Phases of matter ja:アモルファス

Server

: This article is about computer servers. For food service use, see waiter. In computing, a server is:
- A computer software application that carries out some task (i.e. provides a service) on behalf of yet another piece of software called a client. In the case of the Web: An example of a server is the Apache web server, and an example of a client is the Internet Explorer web browser or the Mozilla web browser. Other server (and client) software exists for other services such as e-mail, printing, remote login, and even displaying graphical output. This is usually divided into file serving, allowing users to store and access files on a common computer; and application serving, where the software runs a computer program to carry out some task for the users. This is the original meaning of the term. Web, mail, and database servers are what most people access when using the Internet.
- Over the years, the term has been misinterpreted (but in common usage now) to also mean the physical computer on which the server software runs. Software ultimately requires computer hardware to run, and originally server software would be run on a large powerful computer such as a mainframe computer or minicomputer. These have largely been replaced by computers built using a more robust version of the microprocessor technology than is used in personal computers, and the term "server" was adopted to describe microprocessor-based machines designed for this purpose. In a general sense, "server" machines have high-capacity (and sometimes redundant) power supplies, a motherboard built for durability in 24x7 operations, large quantities of ECC RAM, and fast I/O subsystems employing technologies such as SCSI, RAID, and PCI-X or PCI Express. It is important to note, however, that computers referred to as "servers" do not necessarily run any server software, nor is it required that server software only be run on these types of computers.

Usage

Sometimes this dual usage can lead to confusion, for example in the case of a web server. This term could refer to the machine which stores and operates the websites, and it is used in this sense by companies offering commercial hosting facilities. Alternatively, web server could refer to the software, such as the Apache HTTP server, which runs on such a machine and manages the delivery of web page components in response to requests from web browser client.

Server hardware

A server computer shares its resources, such as peripherals (i.e printer: print server) and file storage (i.e. disk: file server), with the users' computers, called clients, on a network. Thus, it is possible for a computer to be a client and a server simultaneously, by connecting to itself in the same way a separate computer would. Many new devices now come with server capabilities. The X-Internet, Web Services, and Microsoft's .NET initiative all work to make even the smallest system a server. Many large enterprises employ numerous servers to support their needs. A collection of servers in one location is often referred to as a server farm. It is possible to configure the machines to distribute tasks so that no single machine is overwhelmed by the demands placed upon it (called load balancing), and this is often done for hosts that expect tremendous amounts of activity. The terminology can be even more confusing in this case because the client (or user) will connect to a remote host to access the server application, and that server application may need to access other server software and/or another server machine. Servers are normally specialist machines developed over a couple of years to provide the reliability expected by the business users. Servers are not normally available through high street resellers and therefore can only be purchased from branded resellers. Pricing for servers start as low as $700 for small, non redundant servers, while it is possible to specify a single server that costs over $100,000, applications that require this level of computing power are usually run on many smaller servers that are in a load balancing configuration. Due to the continual demand for ever more powerful servers in ever decreasing spaces, companies such as Hewlett Packard, IBM and Dell have developed higher density configurations, the most notable of which is known as the blade server. Blade servers incorporate a number of server computers – sometimes as many as fourteen – each housed inside a high-density module known as a "blade", within the space typically occupied by a single computer.
- [http://www.sun.com/servers/index.jsp SUN Servers]
- [http://www.ibm.com/servers/ IBM Servers]
- [http://welcome.hp.com/country/uk/en/prodserv/servers.html HP Servers]
- [http://www1.us.dell.com/content/topics/segtopic.aspx/products40/categories/en/servers_beta?c=us&cs=555&l=en&s=biz Dell Servers]

Server operating systems

The rise of the microprocessor-based server was facilitated by the development of several versions of the Unix operating system to run on the Intel microprocessor architecture, including Solaris, Linux and FreeBSD. The Microsoft Windows series of operating systems also now includes server versions that support multitasking and other features beneficial for server software, beginning with Windows NT. The current Windows Server version is Windows Server 2003. There are many servers running Linux versions such as Red Hat Linux, SUSE SLES, and Debian, which have generally proven to be more stable than Windows machines. There are an increasing number of servers running Mac OS X as organizations begin to realize the potential and stability that arises from having the hardware and software properly fitted and vetted. Most technical servers continue to be Sun, SGI, or HP workstations as they are proven and generally stable servers.

X Window server

The X Window System can cause some confusion in the understanding of servers and clients. One might expect that the "server" in X would refer to the computer on which individual programs are running and the client to be the computer the human user is physically in front of. In reality, an X server provides access (i.e. service) to computer input and output devices, such as monitors, keyboards, and mice. Thus the X client runs on the computer doing all the internal software computation, while the X server runs on the computer that actually displays the graphical output on its monitor, interacting with a human user. The X Window System (which speaks the X protocol) is able to operate over a network, because it is designed to be client/server based. The only requirement for a client to connect to a server is a network connection. However, in most situations, the server and clients run on the same physical machine. In this case, either UNIX local sockets or a loopback interface act as transparent media for network connections between client and server.

Historical note

Mainframes and minicomputers were originally accessed using dumb terminals, which were unable to carry out any significant processing. This largely ended with the widespread use of personal computers, a.k.a. PCs, by users.

External links

- [http://www.myserver.us/ Directory of Hosting/Server Providers]
- [http://www.cs.rice.ty.edu/CS/Systems/ScalaServer/ System support for scalable network servers]
- [http://www.kegel.com/c10k.html The C10K problem]
- [http://groups.google.de/groups?group=comp.programming.threads&threadm=580fae16.0312210310.1410bf2b%40posting.google.com Discussion "Writing a scalable server"]
- [http://faqs.lomonline.de/what-is-a-server What is a server] als:Server ko:서버 ja:サーバ simple:Server th:เซิร์ฟเวอร์

Workstation

A computer workstation, often colloquially referred to as workstation, is a high-end general-purpose microcomputer designed to be used by one person at a time and which offers higher performance than normally found in a personal computer, especially with respect to graphics, processing power and the ability to carry out several tasks at the same time. The 3Station by 3Com was a typical early example. When comparing with some of the old definitions of computing power, some people may consider a workstation to be the equivalent of a one-person minicomputer. The earliest examples of workstations were generally cheap minicomputers like PDPs which only one person used, despite being intended for a number of users. The first computers consciously designed for one user (and so a workstation in the modern sense of the term) were the Lisp machines developed at MIT ~1974. In the early 1980s, successors in this field were Apollo Computer and Sun Microsystems who created Unix-based workstations based on the Motorola 68000 processor. Workstations tend to be very expensive, typically several times the cost of a standard PC and sometimes costing as much as a new car. The high expense usually comes from using costlier components that (one hopes) run faster than those found at the local computer store. Manufacturers try to take a "balanced" approach to system design, making certain that data can flow unimpeded between the many different subsystems within a computer. Additionally, workstation makers tend to push to sell systems at higher prices in order to maintain somewhat larger profit margins than the commodity-driven PC manufacturers. The systems that come out of workstation companies often feature SCSI or Fibre Channel disk storage systems, high-end 3D accelerators, single or multiple 64-bit processors, large amounts of RAM, and well-designed cooling. Additionally, the companies that make the products tend to have very good repair/replacement plans. However, the line between workstation and PC is increasingly becoming blurred as trends toward consolidation and cost-cutting have caused workstation manufacturers to use "off the shelf" PC components and graphics solutions as opposed to proprietary in-house developed technology. Some attempts have been made to produce low-cost workstations (which are still expensive by PC standards), but they have often had lackluster performance. The fact that consumer products of PCs and game consoles are now themselves at the cutting edge of technology makes deciding whether or not to purchase a workstation very difficult for many organizations. Sometimes, these systems are still required, but many places opt for the less-expensive, if more fault-prone, PC-level hardware.

What makes a workstation?

It is instructive to look at the history of specific technologies which once differentiated workstations from personal computers. The more widespread adoption of these technologies into mainstream PCs was a direct factor in the decline of the workstation as a separate market segment:
- RISC CPUs: while RISC in its early days (early 1980s) offered something like an order-of-magnitude performance improvement over CISC processors of comparable cost, one particular family of CISC processors (Intel's x86) always had the edge in market share and the economies of scale that this implied. By about the mid-1990s, Intel CPUs had achieved performance on a parity with RISC (albeit at a cost of greater chip complexity), relegating the latter to niche markets for the most part.
- Hardware support for floating-point operations: this was standard among higher-end PCs by the late 1980s, but did not become common at the lowest end of the market until the mid 1990s. Now, even the lowest priced PC on the market has it as a standard.
- Operating system: early workstations run on a variant of the Unix operating system. The early 8-bit and 16-bit PC CPUs could not run an OS as sophisticated as Unix, but this, too, began to change from about the late 1980s as PCs with 32-bit CPUs and integrated MMUs became widely affordable.
- High-speed networking (10 Mbit/s or better): common among PCs by the early 1990s.
- Large displays (17"-21"): common among PCs by the late 1990s.
- High-performance 3D graphics hardware: this started to become really popular in the PC market around the mid-to-late 1990s, mostly driven by computer gaming.
- SCSI disk storage: never very popular in the PC market, except for the Apple Macintosh. SCSI was an advanced controller interface which was particularly good where the disk had to cope with multiple requests at once. This made it suited for use in servers, but its benefits to desktop PCs which were mostly running single-user operating systems were less clear. These days, with desktop systems acquiring more multi-user capabilities (and the increasing popularity of Linux), the new disk interface of choice is Serial ATA, which has some SCSI-like speed, but at a lower cost.
- Extremely reliable components: this is actually the most distinctive feature of a workstation. Although most technologies implemented in workstations are available at a much lower price for the consumer market, finding good components and make sure they work compatibly with each other is a great challenge in workstation building. Because workstations are designed for high-end tasks (such as weather forecasting, video rendering, game design...), it's taken for granted that these systems must be running under full-load, non-stop for several hours (if not days) without any problem. Any off-the-shelf components can be used to build a workstation, but they will stop working soon under such rigorious conditions. For this reason, almost no workstation are built by the customer themselves but rather purchased from a vendor such as HP, IBM, SGI or Dell. These days, workstations have changed greatly. They are beginning to use many technologies common to the consumer market as a cost-cutting strategy. For example, some low-end workstations use Intel Pentium 4 or AMD Athlon 64 as their CPUs and Windows as their operating system. Higher-end workstations may use more sophisicated CPUs such as Intel Itanium 2, AMD Opteron, IBM POWER or Sun Microsystems SPARC and run on a variant of Unix delivering a truly reliable workhorse for computing-intensive tasks. Some workstations are designed for use with only one specific application such as AutoCAD, Avid Xpress Studio HD, 3D Studio MAX, ect. To ensure compatibility with the software, purchasers usually ask for a certificate from the software vendor. The certification process make the workstation's price jumps several notches but for professional purposes, reliability is more important than the cost. It is important to note that the PA-RISC, Alpha, and MIPS CPUs are still sold in workstations but are excluded in the above list because they are reaching their end-of-life soon, along with their operating systems (HP-UX, Tru64, and Irix, respectively). While Apple's PowerPC with Mac OS X is a workstation combination, we will need to see what Intel processor will replace the PowerPC. However, most are confident that Apple will use a processor (or have the option of having a processor) that is like (or perhaps the same) as the Xeon processor and continue its share in the workstation market.

List of workstations and manufacturers

Note that many of these are extinct.
- 3Station
- Apollo Computer
- Atari Transputer Workstation
- Datamax UV-1
- Digital Equipment Corporation
- Hewlett Packard
- Intergraph
- Lilith
- NeXT
- Silicon Graphics
- Sun Microsystems
- Unisys ICON
- Xerox Star

Advanced Technology Attachment

Advanced Technology Attachment (ATA) is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. Many terms and synonyms for ATA exist, including abbreviations such as IDE, ATAPI, and UDMA. With the introduction of Serial ATA in 2003, the original ATA was retroactively renamed Parallel ATA (PATA). In line with the original naming, this article only covers Parallel ATA. Parallel ATA standards only allow cable lengths up to 18 inches (up to 450 mm) although cables up to 36 inches (900 mm) can be readily purchased. Because of this length limit, the technology normally appears as an internal computer storage interface. It provides the most common and the least expensive interface for this application.

History

retroactively renamed Although the standard has always had the official name "ATA", marketing dictates dubbed an early version of the standard Integrated Drive Electronics (IDE), and the one following it Enhanced IDE (EIDE). Although these new names originated in branding convention and not as an official standard, the term EIDE often appears interchangeably with IDE and ATA. With the introduction of Serial ATA around 2003, this configuration was retroactively renamed to Parallel ATA (P-ATA), referring to the method in which data travels over wires in this interface. The interface at first only worked with hard disks, but eventually an extended standard came to work with a variety of other devices—generally those using removable media. Principally, these devices include CD-ROM and DVD-ROM drives, tape drives, and large-capacity floppy drives such as the Zip drive and SuperDisk drive. The extension bears the name Advanced Technology Attachment Packet Interface (ATAPI), with the full standard now known as ATA/ATAPI. The movement from programmed input/output (PIO) to direct memory access (DMA) provided another important transition in the history of ATA. As every word must be read by the CPU individually PIO tends to be slow and use a lot of CPU. This is especially a problem on faster CPUs where accessing an address outside of the cacheable main memory (whether in the I/O map or the memory map) is a relatively expensive process. This meant that systems based around ATA devices generally performed disk-related activities much more slowly than computers using SCSI or other interfaces. However, DMA (and later Ultra DMA, or UDMA) greatly reduced the amount of processing time the CPU had to use in order to read and write the disks by allowing the disk controller to write data to memory directly, thus bypassing the CPU. ATA devices have suffered from a number of "barriers" in terms of how much data they can handle. However, new addressing systems and programming techniques have broken most of these barriers. Some of the ATA-specific barriers included: 504 MB, 8 GB, 32 GB, and 137 GB. A variety of other barriers have existed, usually due to device drivers and disk I/O layers in operating systems that did not correspond with ATA standards. The original ATA specification used a 28-bit addressing mode. This allows for the addressing of 268,435,456 512-byte sectors (128 GiB or 137 GB). The standard PC BIOS system supported up to 8 GiB. Unfortunately, when the lowest common denominators of the CHS limit

Cd writer

Compatibility

Performance

See also

External links

Compact disc

History

Physical details

Audio format

Storage capacity

Data structure

Subcode

CD-Text

The AAD, ADD, DDD code for audio CDs

CD-ROM

Recordability

Copy protection

Non-standard CD behaviors

Name

References

See also

CD ROM

Manufacture

Capacity

CD-ROM drives

Copyright Issues

Data Formats

See also

References

External links

CD-R

History

Physical characteristics

Writing methods

Optimal storage conditions and expected lifespan

Cleaning CD-Rs

Readability in CD drives

See also

External links

DVD-R

Capacities

References

See also

External links

DVD plus R

See also

External links

CD-RW

See also

References

External links

DVD-RW

See also

External links

DVD plus RW

See also

External links

Amorphous solid

Glasses

Metallic glass

Other synthesis routes

Damage

Cold Deposition

Toward a strict definition

Server

Usage

Server hardware

Server operating systems

X Window server

Historical note

See also

External links

Workstation

What makes a workstation?

List of workstations and manufacturers

See also

Advanced Technology Attachment

History