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DVDFrom Wikipedia, the free encyclopediaThis article is about the disc format in general. For the video recording format based upon DVD, see DVD-Video. For the audio storage format also based upon DVD, see DVD-Audio. For other uses, see DVD (disambiguation)."MMCD" redirects here. For Sony's proprietary CD-ROM XA-based multimedia software format, see Sony Multimedia CD-ROM Player.
The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc)[8][9] is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind of digital data and has been widely used for video programs (watched using DVD players) or formerly for storing software and other computer files as well. DVDs offer significantly higher storage capacity than compact discs (CD) while having the same dimensions. A standard DVD can store up to 4.7 GB of storage, while variants can store up to a maximum of 17.08 GB.[10] Prerecorded DVDs are mass-produced using molding machines that physically stamp data onto the DVD. Such discs are a form of DVD-ROM because data can only be read and not written or erased. Blank recordable DVD discs (DVD-R and DVD+R) can be recorded once using a DVD recorder and then function as a DVD-ROM. Rewritable DVDs (DVD-RW, DVD+RW, and DVD-RAM) can be recorded and erased many times. DVDs are used in DVD-Video consumer digital video format and less commonly in DVD-Audio consumer digital audio format, as well as for authoring DVD discs written in a special AVCHD format to hold high definition material (often in conjunction with AVCHD format camcorders). DVDs containing other types of information may be referred to as DVD data discs. EtymologyThe Oxford English Dictionary comments that, "In 1995, rival manufacturers of the product initially named digital video disc agreed that, in order to emphasize the flexibility of the format for multimedia applications, the preferred abbreviation DVD would be understood to denote digital versatile disc." The OED also states that in 1995, "The companies said the official name of the format will simply be DVD. Toshiba had been using the name 'digital video disc', but that was switched to 'digital versatile disc' after computer companies complained that it left out their applications."[11] "Digital versatile disc" is the explanation provided in a DVD Forum Primer from 2000[12] and in the DVD Forum's mission statement, which the purpose is to promote broad acceptance of DVD products on technology, across entertainment, and other industries.[13] Because DVDs became highly popular for the distribution of movies in the 2000s, the term DVD became popularly used in English as a noun to describe specifically a full-length movie released on the format; for example the sentence to "watch a DVD" describes watching a movie on DVD.[14] SpecificationsThe DVD specifications created and updated by the DVD Forum are published as so-called DVD Books (e.g. DVD-ROM Book, DVD-Audio Book, DVD-Video Book, DVD-R Book, DVD-RW Book, DVD-RAM Book, DVD-AR (Audio Recording) Book, DVD-VR (Video Recording) Book, etc.).[1][2][3] DVD discs are made up of two discs; normally one is blank, and the other contains data. Each disc is 0.6 mm thick, and are glued together to form a DVD disc. The gluing process must be done carefully to make the disc as flat as possible to avoid both birefringence and "disc tilt", which is when the disc is not perfectly flat, preventing it from being read.[43][44] Some specifications for mechanical, physical and optical characteristics of DVD optical discs can be downloaded as freely available standards from the ISO website.[45] There are also equivalent European Computer Manufacturers Association (Ecma) standards for some of these specifications, such as Ecma-267 for DVD-ROMs.[46] Also, the DVD+RW Alliance publishes competing recordable DVD specifications such as DVD+R, DVD+R DL, DVD+RW or DVD+RW DL. These DVD formats are also ISO standards.[47][48][49][50] Some DVD specifications (e.g. for DVD-Video) are not publicly available and can be obtained only from the DVD Format/Logo Licensing Corporation (DVD FLLC) for a fee of US$5000.[51][52] Every subscriber must sign a non-disclosure agreement as certain information on the DVD Books is proprietary and confidential.[51] Double-sided discsMain article: Double-sided disk Borrowing from the LaserDisc format, the DVD standard includes DVD-10 discs (Type B in ISO) with two recorded data layers such that only one layer is accessible from either side of the disc. This doubles the total nominal capacity of a DVD-10 disc to 9.4 GB (8.75 GiB), but each side is locked to 4.7 GB. Like DVD-5 discs, DVD-10 discs are defined as single-layer (SL) discs.[45] Dual-layer discsDVD hardware accesses the additional layer (layer 1) by refocusing the laser through an otherwise normally-placed, semitransparent first layer (layer 0). This laser refocus—and the subsequent time needed to reacquire laser tracking—can cause a noticeable pause in A/V playback on earlier DVD players, the length of which varies between hardware.[53] A printed message explaining that the layer-transition pause was not a malfunction became standard on DVD keep cases. During mastering, a studio could make the transition less obvious by timing it to occur just before a camera angle change or other abrupt shift, an early example being the DVD release of Toy Story.[54] Later in the format's life, larger data buffers and faster optical pickups in DVD players made layer transitions effectively invisible regardless of mastering.[citation needed] Dual-layer DVDs are recorded using Opposite Track Path (OTP).[55] Combinations of the aboveThe DVD Book also permits an additional disc type called DVD-14: a hybrid double-sided disc with one dual-layer side, one single-layer side, and a total nominal capacity of 12.3 GB.[56] DVD-14 has no counterpart in ISO.[45] Both of these additional disc types are extremely rare due to their complicated and expensive manufacturing.[56] For this reason, some DVDs that were initially issued as double-sided discs were later pressed as two-disc sets.
DVD recordable and rewritableMain article: DVD recordable HP initially developed recordable DVD media from the need to store data for backup and transport.[57][failed verification] DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW, DVD+R/RW (plus), and DVD-RAM. DVD-R is available in two formats, General (650 nm) and Authoring (635 nm), where Authoring discs may be recorded with CSS encrypted video content but General discs may not.[58] Dual-layer recordingDual-layer recording (occasionally called double-layer recording) allows DVD-R and DVD+R discs to store nearly double the data of a single-layer disc—8.5 and 4.7 gigabyte capacities, respectively.[59] The additional capacity comes at a cost: DVD±DLs have slower write speeds as compared to DVD±R.[60] DVD-R DL was developed for the DVD Forum by Pioneer Corporation; DVD+R DL was developed for the DVD+RW Alliance by Mitsubishi Kagaku Media (MKM) and Philips.[61] Recordable DVD discs supporting dual-layer technology are backward-compatible with some hardware developed before the recordable medium.[61] Capacity
All units are expressed with SI/IEC prefixes (i.e., 1 Gigabyte = 1,000,000,000 bytes).
All units are expressed with SI/IEC prefixes (i.e., 1 Gigabyte = 1,000,000,000 bytes).
All units are expressed with SI/IEC prefixes (i.e., 1 Gigabyte = 1,000,000,000 bytes). DVD drives and playersSee also: Optical disc drive and DVD player DVD drives are devices that can read DVD discs on a computer. DVD players are a particular type of devices that do not require a computer to work, and can read DVD-Video and DVD-Audio discs. Transfer ratesSee also: DVD recordable § Transfer rates Read and write speeds for the first DVD drives and players were 1,385 kB/s (1,353 KiB/s); this speed is usually called "1×". More recent models, at 18× or 20×, have 18 or 20 times that speed. Note that for CD drives, 1× means 153.6 kB/s (150 KiB/s), about one-ninth as swift.[64][65] See also: CD and DVD writing speed § CD, DVD and Blu-ray writing speeds
DVDs can spin at much higher speeds than CDs – DVDs can spin at up to 32000 RPM vs 23000 for CDs.[68] DVD recordable and rewritable discs can be read and written using either constant angular velocity (CAV), constant linear velocity (CLV), Partial constant angular velocity (P-CAV) or Zoned Constant Linear Velocity (Z-CLV or ZCLV).[69] Due to the slightly lower data density of dual layer DVDs (4.25 GB instead of 4.7 GB per layer), the required rotation speed is around 10% faster for the same data rate, which means that the same angular speed rating equals a 10% higher physical angular rotation speed. For that reason, the increase of reading speeds of dual layer media has stagnated at 12× (constant angular velocity) for half-height optical drives released since around 2005,[g] and slim type optical drives are only able to record dual layer media at 6× (constant angular velocity), while reading speeds of 8× are still supported by such.[74][75][76] Disc quality measurements
The quality and data integrity of optical media is measureable, which means that future data losses caused by deteriorating media can be predicted well in advance by measuring the rate of correctable data errors.[77] Support of measuring the disc quality varies among optical drive vendors and models.[78][79] DVD-VideoMain article: DVD-Video DVD-Video is a standard for distributing video/audio content on DVD media. The format went on sale in Japan on November 1, 1996,[4] in the United States on March 24, 1997, to line up with the 69th Academy Awards that day;[6] in Canada, Central America, and Indonesia later in 1997, and in Europe, Asia, Australia, and Africa in 1998. DVD-Video became the dominant form of home video distribution in Japan when it first went on sale on November 1, 1996, but it shared the market for home video distribution in the United States for several years; it was June 15, 2003, when weekly DVD-Video in the United States rentals began outnumbering weekly VHS cassette rentals.[80] DVD-Video is still the dominant form of home video distribution worldwide except for in Japan where it was surpassed by Blu-ray Disc when Blu-ray first went on sale in Japan on March 31, 2006.[citation needed] SecurityMain article: Content Scramble System The purpose of CSS is twofold:
LongevityLongevity of a storage medium is measured by how long the data remains readable, assuming compatible devices exist that can read it: that is, how long the disc can be stored until data is lost. Numerous factors affect longevity: composition and quality of the media (recording and substrate layers), humidity and light storage conditions, the quality of the initial recording (which is sometimes a matter of mutual compatibility of media and recorder), etc.[95] According to NIST, "[a] temperature of 64.4 °F (18 °C) and 40% RH [Relative Humidity] would be considered suitable for long-term storage. A lower temperature and RH is recommended for extended-term storage."[96] As with CDs, the information and data storage will begin to degrade over time with most standard DVDs lasting up to 30 years depending the type of environment they are stored and whether they are full with data.[97] According to the Optical Storage Technology Association (OSTA), "Manufacturers claim lifespans ranging from 30 to 100 years for DVD, DVD-R and DVD+R discs and up to 30 years for DVD-RW, DVD+RW and DVD-RAM."[98] According to a NIST/LoC research project conducted in 2005–2007 using accelerated life testing, "There were fifteen DVD products tested, including five DVD-R, five DVD+R, two DVD-RW and three DVD+RW types. There were ninety samples tested for each product. ... Overall, seven of the products tested had estimated life expectancies in ambient conditions of more than 45 years. Four products had estimated life expectancies of 30–45 years in ambient storage conditions. Two products had an estimated life expectancy of 15–30 years and two products had estimated life expectancies of less than 15 years when stored in ambient conditions." The life expectancies for 95% survival estimated in this project by type of product are tabulated below:[95][dubious – discuss]
102030405060708090100DVD-RDVD+RDVD-RWDVD+RW
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Note: The above sections regarding disc types pertain to 12 cm discs. The same disc types exist for 8 cm discs: ISO standards still regard these discs as Types A–D, while the DVD Book assigns them distinct disc types. DVD-14 has no analogous 8 cm type. The comparative data for 8 cm discs is provided further down.
