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For the binocular vision condition, see Dissociated Vertical Deviation. For the successor of DVD, see Blu-ray Disc.
DVD, also known as Digital Versatile Disc or Digital Video Disc, is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage. DVDs are of the same dimensions as compact discs (CDs), but store more than six times as much data. Variations of the term DVD often describe the way data is stored on the discs: DVD-ROM (read only memory) has data that can only be read and not written; DVD-R and DVD+R (recordable) can record data only once, and then function as a DVD-ROM; DVD-RW (re-writable), DVD+RW, and DVD-RAM (random access memory) can all record and erase data multiple times. The wavelength used by standard DVD lasers is 650 nm;[4] thus, the light has a red color. DVD-Video and DVD-Audio discs refer to properly formatted and structured video and audio content, respectively. Other types of DVDs, including those with video content, may be referred to as DVD Data discs.
[edit] HistoryIn 1993, two high-definition optical storage formats were being developed. One was the MultiMedia Compact Disc (MMCD), backed by Philips and Sony, and the other was the Super Density (SD) disc, supported by Toshiba, Time Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC.
Representatives of the SD camp approached IBM, asking for advice on the file system to use for their disk as well as looking for support for their format for storing computer data. A researcher from IBM's Almaden Research Center received that request and also learned of the MMCD development project. Wary of being caught in a repeat of the costly videotape format war between VHS and Betamax in the 1980s, he convened a group of computer industry experts, including representatives from Apple, Microsoft, Sun, Dell, and many others. This group was referred to as the Technical Working Group, or TWG. The TWG voted to boycott both formats unless the two camps agreed on a single, converged standard.[5] Lou Gerstner, president of IBM, was recruited to apply pressure on the executives of the warring factions. Eventually, the computer companies won the day, and a single format, now called DVD, was agreed upon. The TWG also collaborated with the Optical Storage Technology Association (OSTA) on the use of their implementation of the ISO-13346 file system (known as Universal Disk Format [UDF]) for use on the new DVDs. Philips and Sony decided it was in their best interest to avoid another format war over their MultiMedia Compact Disc, and agreed to unify with companies backing the Super Density Disc to release a single format with technologies from both. The specification was mostly similar to Toshiba and Matsushita's Super Density Disc, except for the dual-layer option (MMCD was single-sided and optionally dual-layer, whereas SD was single-layer but optionally double-sided) and EFMPlus modulation. EFMPlus was chosen due to its great resilience against disc damage, such as scratches and fingerprints. EFMPlus, created by Kees Immink (who also designed EFM), is 6% less efficient than the modulation technique originally used by Toshiba, which resulted in a capacity of 4.7 GB, as opposed to the original 5 GB. The result was the DVD specification, finalized for the DVD movie player and DVD-ROM computer applications in December 1995. The DVD Video format was first introduced by Toshiba in Japan in November 1996, in the United States in March 1997 (test marketed),[6] in Europe in November 1998, and in Australia in March 1999. In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies.[6] DVD specifications created and updated by 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 Book, DVD-VR Book, etc).[1][2][3] Some specifications for mechanical, physical and optical characteristics of DVD optical disks can be downloaded as freely available standards from ISO website.[7] There is also DVD+RW Alliance, which publish competing DVD specifications such as DVD+R, DVD+R DL, DVD+RW or DVD+RW DL. These DVD formats are also ISO standards.[8][9][10][11] Some of DVD specifications (e.g. for DVD-Video) are not publicly available and can be obtained only from DVD Format/Logo Licensing Corporation for a fee of $ 5000.[12][13] Every subscriber must sign a non-disclosure agreement as certain information in the DVD Book is proprietary and confidential.[12] [edit] EtymologyThe official DVD specification documents have never defined the initialism DVD. Usage in the present day varies, with Digital Versatile Disc, Digital Video Disc, and DVD being the most common. DVD was originally used as an initialism for the unofficial term digital videodisk.[14] It was reported in 1995, at the time of the specification finalization, that the letters officially stood for Digital Versatile Disc (due to nonvideo applications).[15] However, the text of the press release announcing the specification finalization only refers to the technology as "DVD", making no mention of what (if anything) the letters stood for.[6]
The DVD Forum website has a section called "DVD Primer" in which the answer to the question, "What does DVD mean?" reads, "The keyword is 'versatile.' Digital Versatile Discs provide superb video, audio and data storage and access—all on one disc."[17] [edit] DVD capacity
The basic types of DVD (12 cm diameter, single-sided or homogenous double-sided) are referred to by a rough approximation of their capacity in gigabytes. In draft versions of the specification, DVD-5 indeed held five gigabytes, but some parameters were changed later on as explained above, so the capacity decreased. Other formats, those with 8 cm diameter and hybrid variants, acquired similar numeric names with even larger deviation. The 12 cm type is a standard DVD, and the 8 cm variety is known as a MiniDVD. These are the same sizes as a standard CD and a mini-CD, respectively. The capacity by surface (MiB/cm2) varies from 6.92 MiB/cm2 in the DVD-1 to 18.0 MiB/cm2 in the DVD-18. As with hard disk drives, in the DVD realm, gigabyte and the symbol GB are usually used in the SI sense (i.e., 109, or 1,000,000,000 bytes). For distinction, gibibyte (with symbol GiB) is used (i.e., 230, or 1,073,741,824 bytes). Most computer operating systems display file sizes in gibibytes, mebibytes, and kibibytes, labeled as gigabyte, megabyte, and kilobyte, respectively. Each DVD sector contains 2,418 bytes of data, 2,048 bytes of which are user data. There is a small difference in storage space between + and - (hyphen) formats:
[edit] Technology  DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing for a DVD's increased storage capacity. In comparison, Blu-ray, the successor to the DVD format, uses a wavelength of 405 nm, and one dual-layer disc has a 50 GB storage capacity. Writing speeds for DVD were 1×, that is, 1350 kB/s (1,318 KiB/s), in the first drives and media models. More recent models, at 18× or 20×, have 18 or 20 times that speed. Note that for CD drives, 1× means 150 KiB/s (153.6 kB/s), approximately 9 times slower.[20]
[edit] DVD recordable and rewritableMain article: DVD recordable HP initially developed recordable DVD media from the need to store data for backup and transport. DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW (hyphen), DVD+R/RW (plus), and DVD-RAM. [edit] Dual-layer recordingDual-layer recording (sometimes also known as double-layer recording) allows DVD-R and DVD+R discs to store significantly more data—up to 8.54 gigabytes per disc, compared with 4.7 gigabytes for single-layer discs. Along with this, DVD-DL's have slower write speeds as compared to ordinary DVD's and when played on a DVD player, a slight transition can be seen between the layers. DVD-R DL was developed for the DVD Forum by Pioneer Corporation; DVD+R DL was developed for the DVD+RW Alliance by Philips and Mitsubishi Kagaku Media (MKM).[23] A dual-layer disc differs from its usual DVD counterpart by employing a second physical layer within the disc itself. The drive with dual-layer capability accesses the second layer by shining the laser through the first semitransparent layer. In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds.[24] This caused some viewers to worry that their dual-layer discs were damaged or defective, with the end result that studios began listing a standard message explaining the dual-layer pausing effect on all dual-layer disc packaging. DVD recordable discs supporting this technology are backward-compatible with some existing DVD players and DVD-ROM drives.[23] Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, although the blank media remain more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media. There are two modes for dual-layer orientation. With Parallel Track Path (PTP), used on DVD-ROM, both layers start at the inside diameter (ID) and end at the outside diameter (OD) with the lead-out. With Opposite Track Path (OTP), used on many DVD Video discs, the lower layer starts at the ID and the upper layer starts at the OD, where the other layer ends; they share one lead-in and one lead-out. However, some DVD Video discs also use a parallel track, such as those authored episodically, as in a disc with several separate episodes of a TV series—where more often than not, the layer change is in-between titles and therefore would not need to be authored in the opposite track path fashion.[citation needed] [edit] DVD VideoMain article: DVD Video DVD Video is a standard for content on DVD media. In the U.S., mass retailer sales of DVD Video titles and players began in August 1997.[25] By June 2003, weekly DVD Video rentals began outnumbering weekly VHS cassette rentals, reflecting the rapid adoption rate of the technology in the U.S. marketplace.[5][26] Currently, DVD Video is the dominant form of home video distribution worldwide. Although many resolutions and formats are supported, most consumer DVD Video discs use either 4:3 or anamorphic 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL) at 29.97, 25, or 23.976 FPS. Audio is commonly stored using the Dolby Digital (AC-3) or Digital Theater System (DTS) formats, ranging from 16-bits/48 kHz to 24-bits/96 kHz format with monaural to 7.1-channel "Surround Sound" presentation, and/or MPEG-1 Layer 2. Although the specifications for video and audio requirements vary by global region and television system, many DVD players support all possible formats. DVD Video also supports features such as menus, selectable subtitles, multiple camera angles, and multiple audio tracks. [edit] DVD AudioMain article: DVD Audio DVD Audio is a format for delivering high fidelity audio content on a DVD. It offers many channel configuration options (from mono to 7.1 surround sound) at various sampling frequencies (up to 24-bits/48 kHz versus CDDA's 16-bits/44.1 kHz). Compared with the CD format, the much higher-capacity DVD format enables the inclusion of considerably more music (with respect to total running time and quantity of songs) and/or far higher audio quality (reflected by higher sampling rates and greater sample resolution, and/or additional channels for spatial sound reproduction). Despite DVD Audio's superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable in typical listening environments. DVD Audio currently forms a niche market, probably due to the very sort of format war with rival standard SACD that DVD Video avoided. [edit] SecurityMain article: Content Protection for Recordable Media DVD Audio discs employ a DRM mechanism, called Content Protection for Prerecorded Media (CPPM), developed by the 4C group (IBM, Intel, Matsushita, and Toshiba). To date, CPPM has not been "broken", in the sense that DVD Video's CSS has been broken, but ways to circumvent it have been developed.[27] By modifying commercial DVD (Audio) playback software to write the decrypted and decoded audio streams to the hard disk, users can essentially extract content from DVD Audio discs much in the same way they can from DVD Video discs. [edit] Improvements and successionIn 2006, a new format called Blu-ray Disc (BD), designed by Sony, Philips, and Panasonic, was released as the successor to DVD. Another format, HD DVD, competed unsuccessfully with this format in the format war of 2006–08. A dual layer Blu-ray Disc can store 50 GB.[28][29] However, unlike previous format changes (e.g., audio tape to compact disc, VHS videotape to DVD), there is no immediate indication that production of the standard DVD will gradually wind down, as they still dominate, with around 87% of video sales and approximately one billion DVD player sales worldwide. In fact experts claim that the DVD will remain the dominant medium for atleast another 5 years as Blu-Ray technology is still in its introductory phase, write and read speeds being poor as well as the fact of necessary hardware being expensive and not readily available.[5][30] Blu-ray players have struggled partly because the MPEG I-frames stored on DVD discs were based on JPEG, which carries DCT information that can be exploited to improve interpolation for higher resolutions. Consumers initially were also slow to adopt Blu-ray due to the cost[citation needed]. By 2009, 85% of stores were selling Blu-ray Discs. A high-definition TV and appropriate connection cables are also required to take advantage of Blu-ray disc. Some analysts suggest that the biggest obstacle to replacing DVD is due to its installed base; a large majority of consumers are satisfied with DVDs.[31] The DVD succeeded because it offered a compelling alternative to VHS. In addition, Blu-ray players are designed to be backward-compatible, allowing older DVDs to be played since the media are physically identical; this differed from the change from vinyl to CD and from tape to DVD, which involved a complete change in physical medium. This situation can be best compared to the changeover from 78 rpm shellac recordings to 45 rpm and 33⅓ rpm vinyl recordings; because the medium used for the earlier format was virtually the same as the latter version (a disk on a turntable, played using a needle), phonographs continued to be built to play obsolete 78s for decades after the format was discontinued. Manufacturers have announced standard DVD releases well into 2009, and the format remains the preferred one for the release of older television programs and films, with some programs such as Star Trek: The Original Series requiring remastering and replacement of certain elements such as special effects in order to be better received in high-definition viewing.[32] The Holographic Versatile Disc (HVD) is an optical disc technology that may one day hold up to 3.9 terabytes (TB) of information, albeit the current maximum is 500GB. It employs a technique known as collinear holography. The 5D DVD, being developed at the Swinburne University of Technology in Melbourne, Australia, uses a multilaser system to encode and read data on multiple layers. Disc capacities are estimated at up to 10 terabytes, and the technology could be commercially ready within ten years. [33] [edit] DVD as an archival mediumThere are two considerations for an archival medium: obsolescence and durability. If there is no device that can read the medium, it is obsolete and the data is unavailable and thus lost. Durability of DVDs is measured by how long the data may be read from the disc, assuming compatible devices exist that can read it: that is, how long the disc can be stored until data is lost. Five factors affect durability: sealing method, reflective layer, organic dye makeup, where it was manufactured, and storage practices.[34] According to the Optical Storage Technology Association (OSTA), "manufacturers claim life spans 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",[35] although a manufacturer of 24-karat gold-based DVDs claims lifespans of up to 300 years.[36] Of more conventional manufacturing processes, Taiyo Yuden is frequently recommended for longer durability.[34] [edit] DVD consumer rightsDVDs that have commercial movies and television content recorded on them are subject to copyright. The rise of filesharing and "piracy" has prompted many copyright owners to display notices on DVD packaging or displayed on screen when the content is played that warn consumers of the illegality of certain uses of the DVD. Such notices do not always offer a reliable summary of DVD owners' rights.[citation needed] Generally, retail buyers of commercial prerecorded DVDs are free to sell or exchange their property.[citation needed] Arrangements for renting and lending differ more by geography. In the U.S., the right to rent or lend out bought DVDs is protected by the first-sale doctrine under the Copyright Act of 1976. In Europe, rental and lending rights are more limited, under a 1992 European Directive that gives copyright holders broader powers to restrict the commercial renting and public lending of DVD copies of their work. [edit] See also[edit] References
DVD Manufacturing [edit] Further reading
[edit] External links
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