'DVD' (also known as "'Digital Versatile Disc'" and "'Digital Video Disc'")
is a popular
optical disc storage media format used for
data storage. Its main uses are for
movies, software, and data archiving. Most DVDs are of the same dimensions as compact discs (
CDs) but store more than 6 times the data.
The term DVD is used in describing three ways that data is stored on the disks —
DVD-ROM has data which can only be read and not written,
DVD-R can be written once and then functions as a DVD-ROM, and
DVD-RAM holds data that can be re-written multiple times.
In addition, terminology defines the way data is structured on the disk.
DVD-Video and
DVD-Audio discs respectively refer to properly formatted and structured video and audio content. Everything else, including other types of DVD discs with video content, is referred to as a DVD-Data disc. DVD is also used generically to refer to
HD (High Density) video disc formats
Blu-ray and
HD DVD.
History
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 1995.
[1] In May 1997, the
DVD Consortium was replaced by the
DVD Forum, which is open to all other companies.
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.
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.
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 |
The 12 cm type is a standard DVD, and the 8 cm variety is known as a
mini-DVD. These are the same sizes as a standard CD and a
mini-CD, respectively.
'Note:' GB here means
gigabyte, equal to 10
9 (or 1,000,000,000) bytes. Many programs will display
gibibyte (GiB), equal to 2
30 (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.
'Capacity Note:' There is a difference in capacity (storage space) 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 |
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 on one side | DVD-14 |
| Double sided, dual layer on both sides | 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]
Technology
Internal mechanism of a DVD-ROM Drive
DVD uses 650 nm wavelength
laser diode light as opposed to 780 nm for CD. This permits a smaller spot on the media surface that is 1.32 µm for DVD while it was 2.11 µm for CD.
Writing speeds for DVD were 1x, that is 1350
kB/s (1318
KiB/s), in first drives and media models. More recent models at 18x or 20x will have 18 or 20 times that speed. Note that for CD drives, 1x means 153.6 kB/s (150 KiB/s), 9 times slower.
DVD FAQ
DVD recordable and rewritable
Main articles: 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).
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 is comparable to that of single-layer drives, though the blank media remain significantly more expensive.
DVD-Video
Main articles: DVD-Video
'DVD-Video' is a standard for storing video content on DVD media. In the U.S., 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.
DVD-Audio
Main articles: 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. 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.
Security
Main articles: 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.
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, a
HDTV extension to DVD that presaged the HD formats that debuted 6 years after.
[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.
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 medium.
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).
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.
See also
References
1. DVD Format Unification (press release)
2. A Battle for Influence Over Insatiable Disks
3. DVD designers go with AC-3 Final specs for 'digital versatile disc'...
4. DVD FAQ
5. DVD-14
6. Dual Layer Recording burnworld.com
7. Backwards Compatible burnworld.com
8. It's unreel: DVD rentals overtake videocassettes
9. DVD-Audio's CPPM can be got around with a WinDVD patch
10. Sonic Solutions ships New hDVD Format
★
Understanding Recordable & Rewritable DVD
★ Labarge, Ralph. ''DVD Authoring and Production''. Gilroy, Calif.: CMP Books, 2001. ISBN 1-57820-082-2.
★ Taylor, Jim. ''DVD Demystified, 2nd edition''. New York: McGraw-Hill Professional, 2000. ISBN 0-07-135026-8.
External links
Official
★
DVD Forum
★
DVD+RW Alliance
★
DVD Copy Control Association and the Content Scramble System (CSS)
Quality guide
★
Dual Layer Explained – Informational Guide to the Dual Layer Recording Process
Knowledge
★
Understanding Recordable & Rewritable DVD by Hugh Bennett
★
DVD Frequently Asked Questions (and Answers)
★
DVDs: in the fast lane
★
History of DVD technology from the
Consumer Electronics Association
★
How Stuff Works - DVD
العربية
中国
Français
Deutsch
Ελληνική
हिन्दी
Italiano
日本語
Português
Русский
Español
