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DVD-R (pronounced as DVDR or DVD 'minus' R) is a DVD recordable format. A DVD-R has more storage capacity than a CD-R, typically 4.7 GB (or 4.38 GiB) instead of 700 MB, although the capacity of the original standard developed by Pioneer was 3.95 GB (3.68 GiB). Pioneer has also developed an 8.54 GB dual layer version, which appeared on the market in 2005. A DVD-R can be written to only once, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple times.

History

The DVD-R format was developed by Pioneer in autumn of 1997. It is supported by most DVD players, and is approved by the DVD Forum.

Competing formats

A competing format is DVD+R (also DVD+RW for the rewritables), causing some people to refer to DVD-R as DVD 'minus' R unofficially. Hybrid drives that handle both formats are often labeled DVD±R and Super Multi (which includes DVD-RAM support) and are very popular.

Technical specifications

The larger storage capacity of a DVD-R compared to a CD-R is achieved through smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer (see CD-R) a red laser beam with a wavelength of 650 nm (for general use recordable DVD) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength, DVD-R and DVD+R use different dyes from CD-R to properly absorb this wavelength.

DVD-R discs are composed of two 0.6 mm polycarbonate discs, bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver alloy or gold reflector. The other one (for single-sided discs) is an ungrooved 'dummy' disc to assure mechanical stability of the sandwich structure, and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm. Double-sided discs have two grooved, recordable disc sides, and require the user to flip the disc to access the other side. Compared to a CD's 1.2 mm of polycarbonate, a DVD's laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size to write smaller pits.

In a DVD-R, the addressing (the determination of location of the laser beam on the disc) is done with additional pits and lands (called land pre-pits) in the areas between the grooves. The groove on a DVD-R disc has a constant wobble frequency used for motor control etc.


Wikipedia information about DVD-R
. This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article 'DVD-R'








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