By: Michael Sanford
DVD Player - This is a generic term, since there are DVD-Audio, DVD-ROM, DVD-Video players--while DVD-Recordable and DVD-RAM drives are not yet ready for the market. DVD-Video has complex hardware and firmware requirements on the player, and the DVD Player Reference Model specifies the capabilities for a DVD-compliant player for consumer market--outlining the standard and optional sets of features. DVD-Video displays to a TV monitor, but DVD-ROM players will have the hardware (boards) to play DVD-Video and DVD-Audio titles. But, DVD-Video copy protection and regional code issues further complicated and delayed the marketing of players, precluding the implementation of some otherwise acceptable software options, or external devices. It is expected that newer players will implement the required copy protection and regional codes.
DVD 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: their physical dimensions are the same—12cm or the mini 8cm—but they are encoded in a different format and at a much higher density. DVDs contain a file system, called UDF, which is an extension of the ISO 9660 Standard used for CD-ROMs.
DVDs are made from a 0.6 mm thick disc of polycarbonate plastic coated with a much thinner (reflective) aluminum layer. Two such discs are glued together to form a 1.2 mm double-sided disc. The substrates are half as thick as a CD to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks.
A single-layer DVD can store 4.7 Gbyte, which is around seven times as much a standard CD-ROM. By employing a red laser at 650 nm (was 780 nm) wavelength and a numerical aperture of 0.6 (was 0.45), the read-out resolution is increased by a factor 1.65. This holds for two dimensions, so that the actual physical data density increases by a factor of 3.5. DVD uses a more efficient coding method in the physical layer. CD's error correction, CIRC, is replaced by a powerful Reed-Solomon product code, RS-PC; Eight-to-Fourteen Modulation (EFM) is replaced by a more efficient version, EFMPlus, which has the same characteristics as classic EFM. The CD sub code is removed. As a result, the DVD format is 47 percent more efficient with respect to CD-ROM, which uses a 'third' error correction layer.
A DVD can contain:
DVD-Video (containing movies (video and sound))
DVD-Audio (containing high-definition sound)
DVD-Data (containing data)
The disc medium can be:
DVD-ROM (read only, manufactured by a press)
DVD-R/RW (R=Recordable once, RW = Rewritable)
DVD-RAM (random access rewritable)
DVD+R/RW (R=Recordable once, RW = Rewritable)
DVD-R DL (double layer)
DVD+R DL (double layer)
Two DVDs with different bottom sides.
The disc may have one or two sides, and one or two layers of data per side; the number of sides and layers determines the disc capacity.
There are several competing DVD Formats:
DVD-ROM: They are pressed similarly to CDs. The reflective surface is silver or gold colored. They can be single-sided/single-layered, single-sided/double-layered, double-sided/single-layered, or double-sided/double-layered. As of 2004, new double-sided discs have become increasingly rare.
DVD-R for Authoring: Special-purpose DVD-Rs used to record DVD masters, which can then be duplicated to pressed DVDs by a duplication plant. They require a special DVD-R recorder, and are not often used nowadays since many duplicators can now accept ordinary DVD-R masters.
DVD-R discs (strictly DVD-R for General) can record up to 4.7 GB in a similar fashion to a CD-R disc. Once recorded and finalized it can be played by most
DVD-ROM players. This format is supported by the DVD Forum.
DVD-RW discs can record up to 4.7 GB in a similar fashion to a CD-RW drive. Supported by the DVD Forum.
DVD-R DL: Derivate of DVD-R that uses double-layer recordable discs to store up to 8.5 GB of data.
DVD-RAM: (current specification is version 2.1) require a special unit to play 4.7GB or 9.4GB recorded discs (DVD-RAM disc are typically housed in a cartridge). 2.6GB discs can be removed from their caddy and used in DVD-ROM drives. Top capacity is 9.4GB (4.7GB/side). Supported by the DVD Forum.
DVD+R: Can record up to 4.7 GB single-layered/single-sided DVD+R disc, at up to 16x speed. Like DVD-R you can record only once. Supported by the DVD+RW Alliance.
DVD+RW: Can record up to 4.7 GB at up to 16x speed. Since it is rewritable it can be overwritten several times. It does not need special "pre-pits" or finalization to be played in a DVD player. Supported by the DVD+RW Alliance.
DVD+R DL: Derivate of DVD+R that uses double-layer recordable discs to store up to 8.5 GB of data. Supported by the DVD+RW Alliance.
DVD-D is a new self-destructing disposable DVD format. Like the EZ-D, it is sold in an airtight package, and begins to destroy itself by oxidation after several hours.
DVD Plus combines both DVD and CD technologies by providing the CD layer and a DVD layer.
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For more information on DVD players please visit the DVD players resource center at http://www.dvd-players-resources.info
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