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During the early 1990s there were two high density optical storage standards in development; one was the MultiMedia Compact Disc (MMCD), backed by Philips and Sony, and the other was the Super Density Disc (SD), supported by Toshiba, Time-Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC. IBM's president, Lou Gerstner, acting as a matchmaker, led an effort to unite the two camps behind a single standard, anticipating a repeat of the costly format war between VHS and Betamax in the 1980s.

Philips and Sony abandoned their MMCD format and agreed upon Toshiba's SD format with two modifications that are both related to the servo tracking technology. The first one was the adoption of a pit geometry that allows "push-pull" tracking, a proprietary Philips/Sony technology. The second modification was the adoption of Philips' EFMPlus. EFMPlus, created by Kees Immink, who also designed EFM, is 6% less efficient than Toshiba's SD code, which resulted in a capacity of 4.7 Gbyte instead of SD's original 5 Gbyte. The great advantage of EFMPlus is its great resilience against disc damage such as scratches and fingerprints. The result was the DVD specification Version 1.0, announced of 1995, and finalized in September 1996.

The official DVD specification is maintained by the DVD Forum, formerly the DVD Consortium, consisting of the ten founding companies and over 220 additional members. The first DVD players and discs were available in November 1996 in Japan, March 1997 in the United States, 1998 in Europe and in 1999 in Australia.
By the spring of 1999, the price of a DVD player had dropped below the U.S. $300 mark. At that point Wal-Mart began to offer DVD players for sale in its stores. When Wal-Mart began selling DVDs in their stores, DVDs represented only a small part of their video inventory; VHS tapes of movies made up the remainder.

As of 2005, the situation is now completely reversed; most retail stores offer mostly DVDs for sale, while VHS copies of movies are now the minority of sales. The price of a DVD player has dropped to below the level of a typical VCR; a low-end player can be purchased for under US$30 in a number of retail stores. Most, but not all, movie "sets" or series have been released in box sets, as have some entire seasons or selected episode volumes of older and newer television programs.
DVD rentals first topped those of VHS during the week of June 15, 2003. Circuit City and Best Buy stopped selling VHS in 2002 and 2003, respectively. In June 2005, Wal-Mart and several other retailers announced plans to phase out the VHS format entirely, in favor of the more popular DVD format. [1]

In 2000, Sony released its PlayStation 2 console in Japan. In addition to playing video games developed for the system, it was also able to play DVD movies. In Japan, this proved to be a huge selling point due to the fact that the PS2 was much cheaper than many of the DVD players available there. As a result, many electronic stores that normally did not carry video game consoles carried PS2s.
Following on with this tradition Sony has decided to implement one of DVD's possible successors, Blu-ray, into its next PlayStation console currently known as the PlayStation 3. Microsoft's Xbox, released a year after the PlayStation 2, also had the capability to play DVD discs with an add-on kit, cementing the DVD's place in video game consoles.

"DVD" was originally an initialism for "digital video disc"; some members of the DVD Forum believe that it should stand for "digital versatile disc", to indicate its potential for non-video applications. Toshiba, which maintains the official DVD Forum site [2], adheres to the interpretation of "digital versatile disc". The DVD Forum never reached a consensus on the matter, however, and so today the official name of the format is simply "DVD"; the letters do not "officially" stand for anything.[3]

Technical information
DVDs are made from a 0.6 mm thick disc of polycarbonate plastic coated with a much thinner (reflective) aluminium layer. Two such discs are glued together to form a 1.2 mm double-sided disc. The substrates are half as thick as a CD to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks.

A single-layer DVD can store 4.7 Gbyte, which is around seven times as much a standard CD-ROM. By employing a red laser at 650 nm (was 780 nm) wavelength and a numerical aperture of 0.6 (was 0.45), the read-out resolution is increased by a factor 1.65. This holds for two dimensions, so that the actual physical data density increases by a factor of 3.5. DVD uses a more efficient coding method in the physical layer. CD's error correction, CIRC, is replaced by a powerful Reed-Solomon product code, RS-PC; Eight-to-Fourteen Modulation (EFM) is replaced by a more efficient version, EFMPlus, which has the same characteristics as classic EFM. The CD subcode is removed. As a result, the DVD format is 47 percent more efficient with respect to CD-ROM, which uses a "third" error correction layer.

A DVD can contain:

DVD-Video (containing movies (video and sound))
DVD-Audio (containing high-definition sound)
DVD-Data (containing data)
The disc medium can be:

DVD-ROM (read only, manufactured by a press)
DVD-R/RW (R = Recordable once, RW = ReWritable)
DVD-RAM (random access rewritable)
DVD+R/RW (R = Recordable once, RW = ReWritable)
DVD-R DL (double layer)
DVD+R DL (double layer)

Two DVDs with different bottom sides.The disc may have one or two sides, and one or two layers of data per side; the number of sides and layers determines the disc capacity.

DVD-5: single sided, single layer, 4.7 gigabytes (GB), or 4.38 gibibytes (GiB)
DVD-9: single sided, double layer, 8.5 GB (7.92 GiB)
DVD-10: double sided, single layer on both sides, 9.4 GB (8.75 GiB)

DVD-18: double sided, double layer on both sides, 17.1 GB (15.9 GiB)
The capacity of a DVD-ROM can be visually determined by noting the number of data sides, and looking at the data side(s) of the disc. Double-layered sides are sometimes gold-colored, while single-layered sides are silver-colored, like a CD. One additional way to tell if a DVD contains one or two layers is to look at the center ring on the underside of the disc. If there are two barcodes, it is a dual layer disc. If there is one barcode, there is only one layer.

The DVD Forum created the official DVD-ROM/R/RW/RAM standards and the DVD+RW Alliance created the DVD+R/RW standards. Since DVD+R/RW discs are not technically DVDs as per the DVD Forum standards, they are not allowed to display the DVD logo; instead, they display an "RW" logo (even if it is not re-writeable, something some consider deceptive advertising). However, they are readable by most DVD drives, so they are referred to as DVD+R and DVD+RW.

The "+" (plus) and "-" (dash) are similar technical standards and are partially compatible. As of 2004, both formats are equally popular, with about half of the industry supporting "+", and the other half "-". All DVD readers are supposed to read both formats, though real-world compatibility is around 90% for both formats, with DVD-R having the best overall compatibility in independent tests. Most new DVD writers can write both formats and carry both the RW and DVD logos.

Unlike compact discs, where sound (CDDA, Red Book) is stored in a fundamentally different fashion than data (Yellow book et al.), a properly authored DVD will always contain data in the UDF filesystem.

DVD pick-up head and drive.The data transfer rate of a DVD drive is given in multiples of 1350 kB/s, which means that a drive with 16x speed designation allows a data transfer rate of 16 × 1350 = 21600 kB/s (21.09 MB/s). As CD drive speeds are given in multiples of 150 kB/s, one DVD "speed" equals nine CD "speeds", so an 8x DVD drive should have a data transfer rate similar to that of a 72x CD drive. In physical rotation terms (spins per second), one DVD "speed" equals three CD "speeds", so an 8x DVD drive has the same rotational speed as 24x CD drive.Early CD and DVD drives read data at a constant rate. The data on the disc is passed under the read head at a constant rate (Constant Linear Velocity, or CLV). As linear (meters per second) track speed grows at outer parts of the disc proportionally to the radius, the rotational speed of the disc was adjusted according to which portion of the disc was being read. Most current CD and DVD drives have a constant rotation speed (Constant Angular Velocity, or CAV). The maximum data rate specified for the drive/disc is achieved only at the end of the disc's track (discs are written from inside). The average speed of the drive therefore equals to only about 50–70% of the maximum nominated speed. While this seems a disadvantage, such drives have a lower seek time as they do not have to change the disc's speed of rotation.

DVD-Video

Example of how producer could show consumer the full compatibility with DVD-Video specification.
Typical DVD-Video file structure.DVD-Video discs require a DVD-drive with a MPEG-2 decoder (e.g. a DVD-player or a DVD computer drive with a software DVD player). Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and audio of varying formats (often multi-channel formats as described below). Typical data rates for DVD movies range from 3–10 Mbit/s, and the bit rate is usually adaptive. The video resolution on NTSC discs is 720 × 480 and on PAL discs is 720 × 576. A high number of audio tracks and/or lots of extra material on the disc will often result in a lower bit rate (and image quality) for the main feature.

The audio data on a DVD movie can be of the format PCM, DTS, MP2, or Dolby Digital (AC-3). In countries using the NTSC standard any movie should contain a sound track in (at least) either PCM or Dolby AC-3 formats, and any NTSC player must support these two; all the others are optional. This ensures any standard compatible disc can be played on any standard compatible player. The vast majority of commercial NTSC releases today employ AC-3 audio.

Initially, in countries using the PAL standard (e.g. most of Europe) the sound of DVD was supposed to be standardized on PCM and MP2, but apparently against the wishes of Philips, under public pressure on December 5, 1997, the DVD Forum accepted the addition of Dolby AC-3 to the optional formats on discs and mandatory formats in players. The vast majority of commercial PAL releases employ AC-3 audio by now.
DVDs can contain more than one channel of audio to go together with the video content. In many cases, sound tracks in more than one language track are present (for example the film's original language as well as a dubbed track in the language of the country where the disc is being sold).

With several channels of audio from the DVD, the cabling needed to carry the signal to an amplifier or TV can occasionally be somewhat frustrating. Most systems include an optional digital connector for this task, which is then paired with a similar input on the amplifier. The selected audio signal is sent over the connection, typically over RCA connectors or TOSLINK, in its original format to be decoded by the audio equipment. When playing compact discs, the signal is sent in S/PDIF format instead.
Video is another issue which continues to present problems. Current players typically output analog video only, both composite video on an RCA jack, as well as S-Video in the standard connector. However neither of these connectors were intended to be used for progressive video, so yet another set of connectors has started to appear, to carry a form of component video, which keeps the three components of the video, one luminance signal and two color difference signal, as stored on the DVD itself, on fully separate wires (whereas S-Video uses two wires, uniting and degrading the two color signals, and composite only one, uniting and degrading all three signals). The connectors are further confused by using a number of different physical connectors on different player models, RCA or BNC, as well as using VGA cables in a non-standard way (VGA is normally analog RGB—a different, incompatible form of component video). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive. In Europe and other PAL areas, SCART connectors are typically used, which carry both composite and analog RGB interlaced video signals, as well as analog two-channel sound on a single multiwire cable, and which offer a reasonable compromise between video quality—which is superior to S-Video though inferior to progressive component video —and cost. HDMI is a new connection similar to SCART, but it carries High Definition, Enhanced Definition and Standard Definition video. Along with video HDMI also supports up to eight-channel digital audio.

DVD Video may also include one or more subtitle tracks in various languages, including those made especially for the hearing impaired. They are stored as images with transparent background which are overlaid over the video during playback. Subtitles are restricted to four colors (including transparency) and thus tend to look cruder than permanent subtitles on film.

DVD Video may contain Chapters for easy navigation (and continuation of a partially watched film). If space permits, it is also possible to include several versions (called "angles") of certain scenes, though today this feature is mostly used—if at all—not to show different angles of the action, but as part of internationalization to e.g. show different language versions of images containing written text, if subtitles will not do.

A major selling point of DVD Video is that its storage capacity allows for a wide variety of extra features in addition to the feature film itself. This can include audio commentary that is timed to the film sequence, documentary features, unused footage, trivia text commentary, simple games and film shorts.

Restrictions
DVD-Video has four complementary systems designed to restrict the DVD user in various ways: Macrovision, Content Scrambling System (CSS), region codes, and disabled user operations (UOPs).

Content-scrambling system
Many DVD-Video titles use content-scrambling system (CSS) encryption, which is intended to discourage people from making perfect digital copies to another medium or from bypassing the region control mechanism (see below). Usually, users need to install software provided on the DVD or downloaded from the Internet such as WinDVD to be able to view the disc in a computer system.
The CSS system has caused major problems for the inclusion of DVD players in any open source operating systems, since open source player implementations are not officially given access to the decryption keys or license the patents involved in the CSS system. Proprietary software players were also difficult to find on some platforms. However, a successful effort has been made to write a decoder by reverse engineering, resulting in DeCSS. This has led to long-running legal battles and the arrest of some of those involved in creating or distributing the DeCSS code, through the use of the controversial U.S. Digital Millennium Copyright Act, on the grounds that such software could also be used to facilitate unauthorized copying of the data on the discs. But as U.S. law stops at the border of the United States, the rest of the world can enjoy de-scrambling software to bypass the DVD cartel restrictions. A number of software programs have since appeared on the Web to view DVDs on a number of platforms.
The restrictions also prevent people from copying DVDs. In the past few years a large amount of software has been created to make copies such as DVD Shrink, DVD Decrypter

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