DVD

For the binocular vision condition, see Dissociated Vertical Deviation.

DVD

DVD-R read/write side
Media type	Optical disc
Capacity	4.7 GB (single-sided, single-layer) 8.5-8.7 GB (single-sided, double-layer) 9.4 GB (double-sided, single-layer) 17.08 GB (double-sided, double-layer – rare)
Read mechanism	650 nm laser, 10.5 Mbit/s (1×)
Write mechanism	10.5 Mbit/s (1×)
Standard	DVD Forum's DVD Books and DVD+RW Alliance specifications

VCR, also known as Digital Video Disc or Digital Versatile Disc, (デジタルバーサタイルディスク Dejitaru Bāsatairu Disuku) is an optical disc storage media format, and was invented and developed by Philips, Sony, Toshiba, and Time Warner in 1995. Its main uses are video and data storage. DVDs are of the same dimensions as compact discs (CDs), but are capable of storing just under seven times as much data.

Variations of the term DVD often indicate 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; 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.

History

In 1993 two optical disc storage formats were being developed. One was the MultiMedia Compact Disc (MMCD) also called CDi, 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 disc as well as seeking support for their format for storing computer data. Alan E. Bell, 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. 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 Disc 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 because of its great resilience to 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), in Europe in October 1998, and in Australia in February 1999.

In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies. DVD specifications created and updated by the 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.).

Some specifications for mechanical, physical and optical characteristics of DVD optical discs can be downloaded as freely available standards from the ISO website. Also, the DVD+RW Alliance publishes competing DVD specifications such as DVD+R, DVD+R DL, DVD+RW or DVD+RW DL. These DVD formats are also ISO standards.

Some of DVD specifications (e.g. for DVD-Video) are not publicly available and can be obtained only from the DVD Format/Logo Licensing Corporation for a fee of US $5000. Every subscriber must sign a non-disclosure agreement as certain information in the DVD Book is proprietary and confidential.

Etymology

The 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. Later, as reported at the time of the specification finalization in 1995, the letters officially stood for Digital Versatile Disc (due to nonvideo applications).

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.

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."

Identification (MID)

The DVD is made of a spiral groove read or written starting at the center. The form of the groove encodes unalterable identification data known as Media Identification Code (MID). The MID contains data such as the manufacturer and model, byte capacity, allowed data rates (also known as speed) etc...

DVD capacity

Capacity and nomenclature
SS = single-sided, DS = double-sided, SL = single-layer, DL = dual-layer

Designation		Sides	Layers (total)	Diameter	Capacity
				(cm)	(GB)	(GiB)
DVD-1	SS SL	1	1	8	1.46	1.36
DVD-2	SS DL	1	2	8	2.66	2.47
DVD-3	DS SL	2	2	8	2.92	2.72
DVD-4	DS DL	2	4	8	5.32	4.95
DVD-5	SS SL	1	1	12	4.70	4.37
DVD-9	SS DL	1	2	12	8.54	7.95
DVD-10	DS SL	2	2	12	9.40	8.75
DVD-14	DS SL+DL	2	3	12	13.24	12.33
DVD-18	DS DL	2	4	12	17.08	15.90

Capacity and nomenclature of (re)writable discs

Designation		Sides	Layers (total)	Diameter	Capacity
				(cm)	(GB)	(GiB)
DVD-R	SS SL (1.0)	1	1	12	3.95	3.68
DVD-R	SS SL (2.0)	1	1	12	4.70	4.37
DVD-RW	SS SL	1	1	12	4.70	4.37
DVD+R	SS SL	1	1	12	4.70	4.37
DVD+RW	SS SL	1	1	12	4.70	4.37
DVD-R	DS SL	2	2	12	9.40	8.75
DVD-RW	DS SL	2	2	12	9.40	8.75
DVD+R	DS SL	2	2	12	9.40	8.75
DVD+RW	DS SL	2	2	12	9.40	8.75
DVD-RAM	SS SL	1	1	8	1.46	1.36*
DVD-RAM	DS SL	2	2	8	2.65	2.47*
DVD-RAM	SS SL (1.0)	1	1	12	2.58	2.40
DVD-RAM	SS SL (2.0)	1	1	12	4.70	4.37
DVD-RAM	DS SL (1.0)	2	2	12	5.16	4.80
DVD-RAM	DS SL (2.0)	2	2	12	9.40	8.75*

The basic types of DVD (12 cm diameter, single-sided or homogeneous 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 gigabytes, megabytes, and kilobytes, labeled as gigabyte, megabyte, and kilobyte, respectively.

Size comparison: a 12 cm DVD+RW and a 19 cm pencil.

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:

Capacity differences of writable DVD formats

Type	Sectors	Bytes	KB	KiB	MB	MiB	GB	GiB
DVD-R SL	2,298,496	4,707,319,808	4,707,319.808	4,596,992	4,707.320	4,489.250	4.707	4.384
DVD+R SL	2,295,104	4,700,372,992	4,700,372.992	4,590,208	4,700.373	4,482.625	4.700	4.378
DVD-R DL	4,171,712	8,543,666,176	8,543,666.176	8,343,424	8,543.666	8,147.875	8.544	7.957
DVD+R DL	4,173,824	8,547,991,552	8,547,991.552	8,347,648	8,547.992	8,152.000	8.548	7.961

Technology

DVD-RW Drive operating with the protective cover removed.

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 Disc, 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 153.6 kB/s (150 KiB/s), approximately one ninth as fast.

DVD drive speeds

Drive speed	Data rate			~Write time (min)
	(Mbit/s)	(MB/s)	(MiB/s)	SL	DL
1×	10.80	1.35	1.29	61	107
2×	21.60	2.70	2.57	31	54
2.4×	25.92	3.24	3.09	25	45
2.6×	28.08	3.51	3.35	23	41
4×	43.20	5.40	5.15	15	27
6×	64.80	8.10	7.72	10	18
8×	86.40	10.80	10.30	8	13
10×	108.00	13.50	12.87	6	11
12×	129.60	16.20	15.45	5	9
16×	172.80	21.60	20.60	4	7
18×	194.40	24.30	23.17	3	6
20×	216.00	27.00	25.75	3	5
22×	237.60	29.70	28.32	3	5
24×	259.20	32.40	30.90	3	4

Internal mechanism of a drive

See also: optical disc drive

Internal mechanism of a DVD-ROM Drive. See text for details.

This mechanism is shown right side up; the disc is above it. The laser and optical system "looks at" the underside of the disc.

With reference to the photo, just to the right of image center is the disc spin motor, a gray cylinder, with its gray centering hub and black resilient drive ring on top. A clamp (not in the photo, retained in the drive's cover), pulled down by a magnet, clamps the disc when this mechanism rises, after the disc tray stops moving inward. This motor has an external rotor – every part of it that you can see spins.

The gray metal chassis is shock-mounted at its four corners to reduce sensitivity to external shocks, and to reduce drive noise when running fast. The soft shock mount grommets are just below the brass-colored washers at the four corners (the left one is obscured). Running through those grommets are screws to fasten them to the black plastic frame that's underneath.

Two parallel precision guide rods that run between upper left and lower right in the photo carry the "sled", the moving optical read-write head. As shown, this "sled" is close to, or at the position where it reads or writes at the edge of the disc.

A dark gray disc with two holes on opposite sides has a blue lens surrounded by silver-colored metal. This is the lens that's closest to the disc; it serves to both read and write by focusing the laser light to a very small spot. It's likely that this disc rotates half a turn to position a different set of optics (the other "hole") for CDs vs. DVDs.

Under the disc is an ingenious actuator comprising permanent magnets and coils that move the lens up and down to maintain focus on the data layer. As well, the actuator moves the lens slightly toward and away from the spin-motor spindle to keep the spot on track. Both focus and tracking are relatively quite fast and very precise. The same actuator rotates the lens mount half.a turn as described.

To select tracks (or files) as well as advancing the "sled" during continuous read or write operations, a stepping motor rotates a coarse-pitch leadscrew to move the "sled" throughout its total travel range. The motor, itself, is the gray cylinder just to the left of the most-distant shock mount; its shaft is parallel to the support rods. The leadscrew, itself, is the rod with evenly-spaced darker details; these are the helical groove that engages a pin on the "sled".

The irregular orange material is flexible etched copper foil supported by thin sheet plastic; these are "flexible printed circuits" that connect everything to the electronics (which is not shown).

DVD recordable and rewritable

Main article: DVD recordable

File:Faceplate showing both dvd logo.jpg

Faceplate of a DVD Drive supporting both DVD+ and DVD- formats.

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. DVD-R is available in two formats, General (650 nm) and Authoring (635 nm), where Authoring discs may be recorded with encrypted content but General discs may not.[1]

Although most DVD writers can nowadays write the DVD+R/RW and DVD-R/RW formats (usually denoted by "DVD±RW" and/or the existence of both the DVD Forum logo and the DVD+RW Alliance logo), the "plus" and the "dash" formats use different writing specifications. Most DVD readers and players will play both kinds of discs, although older models can have trouble with the "plus" variants.

Dual-layer recording

Dual-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-DLs have slower write speeds as compared to ordinary DVDs 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).

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. 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. 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 Digital 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 DVDs 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.

DVD-Video

Main article: DVD-Video

DVD-Video is a standard for content on DVD media. The format went on sale in Japan on November 1, 1996, in the United States on March 1, 1997, in Europe on October 1, 1998 and in Australia on February 1, 1999. DVD became the dominant form of home video distribution in Japan when it first went on sale in 1996, but did not become the dominant form of home video distribution in the United States until June 15, 2003, when weekly DVD-Video in the United States rentals began outnumbering weekly VHS cassette rentals, reflecting the rapid adoption rate of the technology in the U.S. marketplace. Currently, DVD-Video is the dominant form of home video distribution worldwide, although it was surpassed by Blu-ray Disc in Japan when Blu-ray first went on sale in Japan on March 31, 2006.

Although many resolutions and formats are supported, most consumer DVDs use either 4:3 or anamorphic 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720/704×480 (NTSC) or 720/704×576 (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 6.1-channel "Surround Sound" presentation, and/or MPEG-1 Layer 2 and/or LPCM Stereophonic. 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.

Security

Main article: Content Scramble System

Consumer Rights

The rise of filesharing and "piracy" has prompted many copyright holders 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. It is commonplace to include a 90 second advert warning that most forms of copying the contents is illegal. Many DVDs prevent skipping past or fast-forwarding through this warning, forcing the consumer to watch.

Arrangements for renting and lending differ by geography. In the U.S., the right to re-sell, 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.

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 (up to 24-bits/192 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.

Security

Main 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).

Although CPPM was supposed to be much harder to crack than DVD Video's CSS, it too was eventually cracked in 2007 with the release of the dvdcpxm tool. The subsequent release of the libdvdcpxm library (which is based on dvdcpxm) allowed for the development of open source DVD-Audio players and ripping software, such as DVD-Audio Explorer. As a result, making 1:1 copies of DVD-Audio discs is now possible with relative ease, much like DVD-Video discs.

Improvements and succession

Blu-ray Disc

In 2006, a new format called Blu-ray Disc (BD), designed by Philips, Sony, Samsung, and Panasonic, was released as the successor to DVD. Another format, HD DVD (developed by the DVD Forum), competed unsuccessfully with this format in the format war of 2006–2008. A dual layer Blu-ray Disc can store 50 to 100 GB.

However, unlike previous format changes, e.g., audio tape to compact disc or 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 at least another five 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.

Consumers initially were also slow to adopt Blu-ray due to the cost. By 2009, 85% of stores were selling Blu-ray Discs. A high-definition television 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. 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 disc on a turntable, played using a needle), phonographs continued to be built to play obsolete 78s for decades after the format was discontinued. Manufacturers continue to release standard DVD titles as of 2010, 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. In the case of Doctor Who, a series primarily produced on videotape between 1963 and 1989 (and thus expected to be difficult to upconvert to high definition), BBC Video reportedly intends to continue issuing DVD-format releases of that series until at least November 2013.

Holographic Versatile Disc

The Holographic Versatile Disc (HVD) is an optical disc technology that may one day hold up to 3.9 terabytes (TB) of information, although the current maximum is 500GB. It employs a technique known as collinear holography.

5D DVD

The 5D DVD, being developed in 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.

DVD as a backup medium

There are two considerations for a backup medium: obsolescence and durability. If the specifications of the DVD format are not preserved and there is no device that can read the medium, it might be hard to re-create devices that can read DVDs, making it very hard to retrieve the data.

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.

The longevity of the ability to read from a DVD+R or DVD-R, is largely dependent on manufacturing quality ranging from 2 to 15 years, and is believed to be an unreliable medium for backup unless great care is taken for storage conditions and handling.

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".

See also

• Book type
• Content Scramble System
• Digital video recorder (DVR)
• DVD authoring
• DVD region code
• DVD TV game
• Evita (First film to be ever be released on DVD.)
• IFO, BUP and VOB

Further reading

• Bennett, Hugh (April 2004). "Understanding Recordable & Rewritable DVD". Optical Storage Technology Association. Retrieved 2006-12-17.
• 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

• DVD at the Open Directory Project
• Dual Layer Explained – Informational Guide to the Dual Layer Recording Process
• DVD Frequently Asked Questions (and Answers)
• DVD Burning and Ripping: A Primer, A Glossary
• YouTube: Segment from 1997 Toshiba DVD demo disc – Technical information about the then-new DVD format, from "DVD Gallery," an in-store demonstration disc from Toshiba.