|Media type||Optical disc|
|Capacity||~4.7 GB (single-sided single-layer), ~8.54 GB (single-sided double-layer)|
|Read mechanism||650 nm laser, 10.5 Mbit/s (1×)|
|Write mechanism||10.5 Mbit/s (1×)|
|Usage||Data storage, video, audio, games|
DVD (also known as "Digital Versatile Disc" or "Digital Video Disc" - see Etymology) 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 which can only be read and not written, DVD-R and DVD+R can only record data 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).
|Optical media types|
In 1993, two high-density optical storage formats were being developed; one was the MultiMedia Compact Disc (MMCD), 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 disk as well as looking for support for their format for storing computer data. 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 of 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 Disk Format (UDF), for use on the new DVDs.
Philips and Sony abandoned their MultiMedia Compact Disc and agreed upon a spec 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 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. The DVD-Video format was introduced first, in 1996, in Japan, to the United States in March 1997 (Test Marketed), mid-late 1998 in Europe and early 1999 in Australia. In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies. 
"DVD" was originally used as an initialism for the unofficial term "digital video disc". 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). 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.
The official DVD specification documents have never defined DVD. Usage in the present day varies, with "DVD", "Digital Video Disc", and "Digital Versatile Disc" being the most common.
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."
 DVD capacity
The basic types of DVD are referred to by a rough approximation of their capacity in gigabytes.
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. The capacity by surface (MiB/cm²)differs from 6.92MiB/cm² in the DVD-1 to 18.0 MiB/cm² in the DVD-18
Note: 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 gibibytes, mebibytes and kibibytes labeled as gigabyte, megabyte and kilobyte respectively.
Each DVD sector contains 2418 bytes of data, 2048 bytes of which are user data.
There is a small difference in storage space between ‘+’ and ‘-’ formats:
DVD uses 650nm wavelength laser diode light as opposed to 780 nm for CD or 405 nm for HD-DVD or Blu-ray Disc. This permits a smaller pit to be etched on the media surface (1.32 µm for DVD versus 1.6 µm for CD) compared to CDs.
Writing speeds for DVD were 1×, that is 1350 kB/s (1318 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 150 KiB/s (153.6 kB/s), approximately 9 times slower.
|Drive speed||Data rate||~Write time (min)|
 DVD recordable and rewritable
HP initially developed recordable DVD media from the need to store data for back-up and transport.
 Dual layer recording
Dual Layer recording allows DVD-R and DVD+R discs to store significantly more data, up to 8.5 gigabytes per side, 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).
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 can exhibit a noticeable pause in some DVD players, 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, though the blank media remains 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 DVD-Video, 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.
DVD-Video is a standard for storing video content on DVD media. In the U.S., mass retailer sales of DVD-Video titles and players began in late 1997. By June 2003, weekly DVD-Video rentals began out-numbering 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.
Though many resolutions and formats are supported, most consumer DVD-Video discs use either 4:3 or anamorphic 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL) at 29.97 or 25 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 7.1 channel "Surround Sound" presentation, and/or MPEG-1 Layer 2. 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 like menus, selectable subtitles, multiple camera angles, and multiple audio tracks.
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 CDDAs 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 bit-depth, 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.
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. 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.
In 2006, a new format called Blu-ray Disc (BD), designed by Sony, Philips, and Panasonic, was released as the successor to DVD. Another format, HD DVD, competed unsuccessfully with this format in the format war of 2006 to 2008.
However, unlike previous format changes (e.g. vinyl records to compact disc, 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 97% of video sales and with approx: one billion DVD player sales world wide. Consumers initially were slow to adopt Blu-ray, partly due to the cost. Currently Blu-ray players are selling for $298 USD or more, while titles retail for as little as $9 USD or higher (but are usually higher in price than SD DVD releases). One also requires a high-definition TV and appropriate connection cables 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 had succeeded because it offered a compelling alternative to VHS. In addition, Blu-ray players are designed to be backwards 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 33 1/3 rpm vinyl recordings; since the medium used for the earlier format was virtually the same as the latter version (a disk on a turntable, played using a needle), phonographs continued to be built to play obsolete 78s for decades after the format was discontinued. Manufacturers have announced standard DVD releases well into 2009, 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 reediting and replacement of certain elements such as special effects in order to be better received in high-definition viewing.