DVD
DVD
In 1995, Philips and Sony introduced the digital video disc (DVD, also “digital versatile disc”), which had the same dimensions as a standard compact disk (CD) but could store up to 4.7 gigabytes of data. This is more than six times the capacity of a CD (700 megabytes). DVD players use a higher-power laser than that used for CDs, which enables smaller pits (0.4 micrometer) and separation tracks (0.74 micro-meter) to be used.
To record a DVD, semiconductor red lasers with wavelengths of 630 nm burn pits onto a glass master disc. Pressings of this surface are covered with clear plastic to make mass-produced copies. The peaks and valleys—called “lands” and “pits”—are interpreted as binary numbers by a reading device, whether computer or DVD player. To increase the amount of information stored, video data may be compressed using a form of lossy compression such as MPEG-2, an industry standard for audio and video sanctioned by a governing body called the Moving Pictures Experts Group. This technology strips unnecessary or redundant data from videos. The compression allows 135 minutes on a single side of an optical disc. Some DVD discs use two sides of the disc for longer movies, while others put a wide-screen version on one side of the disc and a standard 4:3 version on the other. But this was simply the first incarnation of DVD. Some discs now feature a dual-layer technology, meaning that a single side of the disc actually holds two separate MPEG video streams, like an upstairs/downstairs apartment. This allows a single side of the disc to hold 4 1/2 hours of video. Soon, there will be dual-sided/dual-layer discs, which will double the capacity to nine hours.
Most DVDs are write-once read-only disks. DVD-RWs are now available for home use, allowing the user to record data on the DVD. These DVD-RW drives can also handle CD-R, CD-RW, and DVD-R discs. DVD-RWs, like CD-RWs, hold slightly less data than their write-once and read-only counterparts.
New technology pioneered by several major companies, such as Pioneer, introduced a rewriting method known as phase-change recording. To re-record, the disk is reheated with a laser at a different phase than the initial recording. The laser light hits the disk at a slightly different angle, changing the shape of the grooves. The data layer does not experience wear and tear because DVDs are read by laser light and never physically touched by mechanics. The data layer is coated with a protective plastic substrate.
The DVD offers the capability to display movies in three different ways. The wide-screen format provides a special anamorphic video signal that, when processed by a wide-screen television set, fills the entire screen and delivers optimum picture quality. Pan and Scan fills the screen of traditional 4:3 television sets with an entire picture, much like watching network movies. The Letterbox mode provides horizontal bands at the top and bottom to, in essence, create a wide-screen picture in a traditional television set.
DVD-Video supports multiple aspect ratios. Video stored on a DVD in 16:9 format is horizontally squeezed to a 4:3 (standard TV) aspect ratio. On wide-screen TVs, the squeezed image is enlarged by the TV to an aspect ratio of 16:9. DVD video players output wide-screen video in three different ways: letterbox (for 4:3 screens), pan and scan (for 4:3 screens), anamorphic or unchanged (for wide screens).
At the moment, DVD players resemble VCRs, however the race is on to make DVD players smaller and less expensive. Several companies developed a DVD player the size of a personal CD player with an integrated liquid crystal display viewing panel and speakers. A Chinese manufacturer incorporated the DVD player with the TV itself. Higher capacity and higher definition is not far off.
At the January, 2000 Consumer Electronics Show, Pioneer showed off its high-definition DVD Recorder. High-definition DVD (HD-DVD), storing 15 GB in two layers for a total storage capacity of 30 GB, became a reality when violet-blue and blue lasers, emitting wavelengths of 400–430 nm, and less, were perfected. A shorter wavelength laser increases the amount of information stored on an optical disk. Each time the wavelength is halved, the corresponding storage media can contain four times more data. The first commercial HD-DVD player was released for sale in the U.S. in March, 2006. A format called the Blu-ray DVD, which stores 50 GB per disc, has also been developed, and machines capable of handling Blu-ray discs were also shipped to the U.S. market starting in 2006. Four-layer Blu-Ray DVDs holding 100 GB have been demonstrated.
In order to promote the technology and establish a consensus on format standards, ten companies organized the DVD Consortium in 1995. These companies included: Hitachi, Ltd., Matsushita Electronic Industrial Co., Ltd., Mitsubishi Electric Corp., Philips Electronics N.V., Pioneer Electronics Corp., Sony Corp., THOMSON multimedia, Time Warner Inc., Toshiba Corp. and Victor Company of Japan Ltd. Today, the Forum boasts 122 member companies, including electronics manufacturers, software firms, and media companies worldwide.
Resources
BOOKS
Barlow, Aaron. The DVD Revolution: Movies, Culture, and Technology. New York: Praeger Publications, 2004.
OTHER
Optical Storage Technology Association. “Understanding Recordable and Rewriteable DVD.” 2004. <http://www.osta.org/technology/dvdqa/> (accessed October 25, 2006).
Laurie Toupin