DVD Functional Principle

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9. DVD-RW 11
10. DVD+RW 11
11. DVD VIDEO 12
13. DVD AUDIO 13

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DVD (also known as "Digital Versatile Disc" or "Digital Video Disc") is a popular optical disc storage media format. Its main uses are video and data storage. Most 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 has data that can only be read and not written, DVD-R and DVD+R can record data only once and then function as a DVD-ROM. DVD-RW, DVD+RW and DVD-RAM can both record and erase data multiple times. The wavelength used by standard DVD lasers is 650 nm and thus has a red color.
DVD-Video and DVD-Audio discs respectively refer to properly formatted and structured video and audio content. Other types of DVDs, including those with video content, may be referred to as DVD-Data discs. As next generation high-definition optical formats also use a disc identical in some aspects yet more advanced than a DVD, such as Blu-ray Disc, the original DVD is occasionally given the retronym SD DVD (for standard definition). 
DVD-R is a DVD recordable format. A DVD-R typically has a storage capacity of 4.71 GB (or 4.39 GiB), although the capacity of the original standard developed by Pioneer was 3.95 GB (3.68 GiB). Both values are significantly larger than the storage capacity of its optical predecessor, the 700 MB CD-R - a DVD-R has 6.4 times the capacity of a CD-R. Pioneer has also developed an 8.54 GB dual layer version, DVD-R DL, which appeared on the market in 2005.
Data on a DVD-R cannot be changed, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple (1000+) times. DVD-R(W) is one of three competing industry standard DVD recordable formats; the others are DVD+R(W) and DVD-RAM.
A DVD+R is a once-writable optical disc with 4.7 GB (4.377 GiB) of storage capacity (more precisely, 2295104 sectors of 2048 bytes each). It has slightly less storage capacity than the DVD-R (4.382 GiB). The format was developed by a coalition of corporations, now known as the DVD+RW Alliance, in mid 2002 (though most initial advocacy was from Sony). Since the DVD+R format is a competing format to the DVD-R format, which is developed by the DVD Forum, it had not been approved by the DVD Forum, which claimed that the DVD+R format was not an official DVD format until 2008-01-25.
In October 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.
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 non-volatile data storage, audio, or video. This can cause confusion because the DVD+RW Alliance logo is a stylized "RW". Thus, a DVD+R disc can have the RW logo, but it is not rewritable.
The DVD+R format is divergent from the DVD-R format. Hybrid drives that can handle both, often labelled "DVD+-RW", are very popular since there is not a single standard for recordable DVDs. There are a number of significant technical differences between the "minus" and the "plus" format, though most users would not notice the difference. One example is the DVD+R style ADIP (ADdress In Pregroove) system of tracking and speed control being less susceptible to interference and error than the LPP (Land Pre Pit) system used by DVD-R, which makes the ADIP system more accurate at higher speeds. In addition, DVD+R(W) has a more robust error management system than DVD-R(W), allowing for more accurate burning to media independent of the quality of the media. Additional session linking methods are more accurate with DVD+R(W) versus DVD-R(W), resulting in fewer damaged or unusable discs due to buffer under-run and multi-session disks with fewer PI/PO errors. 
Like other "plus" media, it is possible to change the book type to increase the compatibility of DVD+R media. 
As of 2007, the market for recordable DVD technology shows little sign of settling down in favour of either the "dash" or "plus" 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. However, because the DVD-R format has been in use since 1997, it has had a five-year lead on DVD+R. As such, older or cheaper DVD players (up to 2004 vintage) are more likely to favour the DVD-R standard exclusively, and when creating DVDs for distribution (where the playing unit is unknown or older) the DVD-R format would normally be preferable.
On 2008-01-25, DVD6C officially accepted DVD+R and DVD+RW by adding them to its list of licensable DVD products. 
The DVD evolved from the compact disc (CD), first introduced in the 1980s. CDs were primarily used for audio recordings. Attempts to design CDs that could store and play back digital video recordings began in the late 1980s. However, the existing digital data compression coding called MPEG-1 produced picture quality that was generally no better than that from videotapes, then the format most widely used for video and motion picture recordings for home use. It was also not possible to easily fit a two-hour motion picture on a single CD-size disc. The commercial format then available for home viewing of motion pictures with high-quality video and audio was the laserdisc (LD), which first reached the market in 1978. A laserdisc was a double-sided disc about the size of a 12-in vinyl record. It was read with a laser and was played using analog technology. 
An important breakthrough in digital technology came with the development of MPEG-2 compression coding in 1994. MPEG-2, like MPEG-1, was developed by the Moving Picture Experts Group (MPEG). MPEG-2 allowed a two-hour motion picture to be fitted on a CD-size disc with excellent video and audio quality. 
Initially, two incompatible formats for digital video discs were developed: the Multimedia Compact Disc (MMCD) from Sony and the Super Density (SD) digital video disc from Toshiba. Fearing a repeat of the marketing battle between the incompatible Beta and VHS videotape formats, the industry eventually agreed on a single format for the new digital video disc that combined features from both the Sony and Toshiba products, and was compatible with personal computers. The first DVDs and DVD players reached the consumer market in 1997. 
As the players improved and the number of available motion picture titles expanded in the early 2000s, the DVD market grew rapidly and quickly replaced videotapes and laserdiscs as the top format for home viewing. DVD rentals also quickly surpassed videotape rentals. DVDs could offer extra features, including commentary tracks, additional scenes, and interviews, as well as surround-sound audio. The discs also did not suffer regular physical wear the way videotapes did. 
The tremendous success of DVDs overlapped the growth of new television technology such as large, flat screens with higher resolution and improved picture quality. The introduction of high-definition television (HDTV) posed a challenge, however. Standard DVDs cannot produce a true high-definition picture, which has up to five times the resolution of regular television. 
Efforts to develop a DVD designed for high-definition video during the early 2000s resulted in two incompatible formats: Blu-ray, developed by Sony, and HD-DVD, developed by Toshiba. Unlike with the introduction of regular DVDs, the industry did not immediately reach a consensus on a single technology, forcing a battle between high-definition formats in the marketplace. Companies that produced video or gaming products had to choose between Blu-ray or HD-DVD as formats for their high-definition video and motion picture material, or for their computer and electronic games. Although some motion picture titles were released in both formats, most motion picture companies opted to use one format exclusively. 
After most major studios and retail chains chose to use or sell the Blu-ray format, Toshiba announced in early 2008 that it would no longer develop, manufacture, or market HD-DVD players and recorders, in effect scrapping HD-DVD technology. Still to be determined is whether large numbers of consumers will embrace the more expensive high-definition technology in place of standard DVD.

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