Digital Video Disc (DVD)

Media type: optical disc
Capacity: 4.7 GB (single layer), 8.5 GB (dual layer)
Usage: Data storage, video

DVD ("Digital Versatile Disc" or "Digital Video Disc") is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. DVDs resemble Compact Discs in that they have the exact appearance (i.e. diameter: 120mm or 4.72in., occasionally 80mm or 3.15in.) and both are optical storage media so similar that a DVD reader or writer can usually read CDs, but DVDs are encoded in a different format of much greater density, allowing a data storage capacity 8 times greater (single-layer, single-sided).

All read-only DVD discs, regardless of type, are DVD-ROM discs. This includes replicated (factory pressed), recorded (burned), video, audio, and data DVDs. A DVD with properly formatted and structured video content is a DVD-Video disc. DVDs with properly formatted and structured audio content are DVD-Audio discs. Everything else, (including other types of DVD discs with video content) is referred to as a DVD-Data disc. Consumers use the term "DVD-ROM" to refer to pressed data discs only, but that is grammatically incorrect, moreover, the term DVD also is applied generically in describing newer video disc formats, Blu-ray Disc and HD DVD.

Contents [hide]
1 History
1.1 Etymology
2 DVD disc capacity
2.1 Capacity nomenclature
3 DVD recordable and rewriteable
4 Dual layer recording
5 DVD-Video
6 DVD-Audio
6.1 Security
7 Competitors and successors
8 See also
9 References
10 External links
10.1 Official
10.2 Quality guide
10.3 Knowledge



[edit] History

Optical disc authoring
Optical disc
Optical disc image
Recorder hardware
Authoring software
Recording technologies
Recording modes
Packet writing

Optical media types
Laserdisc
Compact Disc/CD-ROM: CD-R, CD-RW
MiniDisc
DVD: DVD-R, DVD-R DL, DVD+R,
DVD+R DL, DVD-RW, DVD+RW,
DVD-RW DL, DVD+RW DL, DVD-RAM
Blu-ray Disc: BD-R, BD-RE
HD DVD: HD DVD-R: HD DVD-RAM
UDO
UMD
Holographic data storage
3D optical data storage
History of optical storage media

Standards
Rainbow Books
File systems
ISO 9660
Joliet
Rock Ridge
Amiga Rock Ridge extensions
El Torito
Apple ISO9660 Extensions
Universal Disk Format
Mount Rainier


Size comparison: A 12cm Sony DVD+RW and a 19cm Dixon Ticonderoga pencil.In the early 1990s two high-density optical storage standards were being developed; one was the MultiMedia Compact Disc, backed by Philips and Sony, and the other was the Super Density disc, 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 videotape format war between VHS, Betamax and Video 2000 in the 1980s.

Philips and Sony abandoned their MultiMedia Compact Disc and fully agreed upon Toshiba's SuperDensity Disc with only one modification, namely changing to EFMPlus modulation. EFMPlus was chosen as it has a 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 of 1995.[1] In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies.


[edit] Etymology
"DVD" was originally used as an initialism for the unofficial term "digital videodisk".[2] It was reported in 1995, at the time of the specification finalization, that the letters officially stood for "digital versatile disc" (due to non-video applications)[3], 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.[1] A newsgroup FAQ written by Jim Taylor (a prominent figure in the industry) claims that four years later, in 1999, the DVD Forum stated that the format name was simply the three letters "DVD" and did not stand for anything.[4] The official DVD specification documents have never defined DVD. Usage in the present day varies, with "DVD", "Digital Video Disc", and "Digital Versatile Disc" all being common.


[edit] DVD disc capacity
Single layer capacity Dual/Double layer capacity
Physical size GB GiB GB GiB
12 cm, single sided 4.7 4.38 8.5 7.92
12 cm, double sided 9.4 8.75 17.1 15.93
8 cm, single sided 1.4 1.30 2.6 2.42
8 cm, double sided 2.8 2.61 5.2 4.84

Note: GB here means gigabyte, equal to 109 (or 1,000,000,000) bytes. Many programs will display gibibyte (GiB), equal to 230 (or 1,073,741,824) bytes.

Example: A disc with 8.5 GB capacity is equivalent to: (8.5 × 1,000,000,000) / 1,073,741,824 ≈ 7.92 GiB.

Size Note: There is a difference in size between + and - DL DVD formats. For example, the 12 cm single sided disk has capacities:

Disk Type Sectors bytes GB GiB
DVD-R SL 2,298,496 4,707,319,808 4.7 4.384
DVD+R SL 2,295,104 4,700,372,992 4.7 4.378
DVD-R DL 4,171,712 8,543,666,176 8.5 7.957
DVD+R DL 4,173,824 8,547,991,552 8.5 7.961


[edit] Capacity nomenclature
The four basic types of DVD are referred to by their capacity in gigabytes, rounded up to the nearest integer.

DVD type Name
Single sided, single layer DVD-5
Single sided, dual layer DVD-9
Double sided, single layer DVD-10
Double sided, dual layer DVD-18

Another format in limited use is a double sided DVD with one side comprising a single layer of data while the opposite side comprises two layers of data (effectively a DVD-5 on one side bonded to a DVD-9 on the other). This format holds approximately 13.2 GB of data and is known as DVD-14.[5]


[edit] DVD recordable and rewriteable
Main article: DVD recordable
HP initially developed recordable DVD media from the need to store data for back-up and transport.

DVD recordables are now also used for consumer audio and video recording. Three formats were developed: -R/RW (minus/dash), +R/RW (plus), -RAM (which is strictly speaking not random access memory).


[edit] Dual layer recording
Dual Layer recording allows DVD-R and DVD+R discs to store significantly more data, up to 8.5 Gigabytes per disc, compared with 4.7 Gigabytes for single-layer discs. 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). [6]

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 semi-transparent layer. The layer change mechanism in some DVD players can show a noticeable pause, as long as two seconds by some accounts. This caused more than a few 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.[7] Many current DVD recorders support dual-layer technology, and the price point is comparable to that of single-layer drives, though the blank media remain significantly more expensive.


[edit] DVD-Video
Main article: DVD-Video
DVD-Video is a standard for storing video content on DVD media. In the US, weekly DVD-Video rentals first out-numbered weekly VHS cassette rentals in June 2003, illustrating the rapid adoption rate of the technology in the marketplace.[8]

Though many resolutions and formats are supported, most consumer DVD-Video disks use either 4:3 or 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL). Audio is commonly stored using the Dolby Digital (AC-3) and/or Digital Theater System (DTS) formats, ranging from monaural to 5.1 channel "Surround Sound" presentations. DVD-Video also supports features like selectable subtitles, multiple camera angles and multiple audio tracks.


[edit] DVD-Audio
Main 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 5.1 surround sound) at various sampling frequencies and sample rates. Compared with the CD format, the much higher capacity DVD format enables the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, 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 to typical human ears. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment.


[edit] Security
Main article: CPRM
DVD-Audio discs employ a robust copy prevention 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.[9] 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] Competitors and successors
There are several possible successors to DVD being developed by different consortiums: Sony/Panasonic's Blu-ray Disc (BD), Toshiba's HD DVD and Maxell's Holographic Versatile Disc (HVD).

In April 2000, Sonic Solutions and Ravisent announced hDVD, an HDTV extension to DVD that presaged the HD formats that debuted 6 years later.[10]

On November 19, 2003, the DVD Forum decided by a vote of eight to six that HD DVD will be its official HDTV successor to DVD. This had no effect on the competing Blu-ray Disc Association's (BDA) determination that its format would succeed DVD, especially since most of the voters belonged to both groups.[citation needed]

On April 15, 2004, in a co-op project with TOPPAN Printing Co., the electronics giant Sony Corp. successfully developed the paper disc, a storage medium that is made out of 51% paper and offers up to 25 GB of storage, about five times more than the standard 4.7 GB DVD. The disc can be easily cut with scissors and recycled offering an environmentally friendly storage media.

As reported in a mid 2005 issue of Popular Mechanics, it is not yet clear which technology will win the format war over DVD. HD DVD discs have a lower capacity than Blu-ray Discs (15 GB vs. 25 GB for single layer, 30 GB vs. 50 GB for dual layer). Other speculations as to which format will win include Blu-ray Disc's larger hardware vendor and movie studio support, and HD DVD's faster read times.

This situation—multiple new formats fighting as the successor to a format approaching purported obsolescence—previously appeared as the "war of the speeds" in the record industry of the 1950s. It is also similar to the VHS/Betamax war in consumer video recorders in the late 1980s.

The new generations of optical formats have restricted access through many various digital rights management schemes such as AACS and HDCP; it remains to be seen what impact the limitation of fair use rights has on their adoption in the marketplace.