DVD and DVD players

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¡ª12cm or the mini
8cm¡ªbut 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.


 
 
About the Author
For more information on DVD players please visit the DVD players resource center at http://www.dvd-players-resources.info


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