DVD-R

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Image:Appledvdr.jpg Image:Dvdrspindle.png Image:Dvdrdisc.png A DVD-Recordable or DVD-R (pronounced "DVD Dash Are", not "DVD Minus Are") is an optical disc with a larger storage capacity than a CD-R, typically 4.7 GB (4.38 GiB) instead of 700 MiB, although the capacity of the original standard was 3.95 GB. 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.

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.

A competing format is [[DVD+R]] (also [[DVD+RW]] for the rewritables). Hybrid drives that handle both formats are often labeled DVD±R and Super Multi (which includes DVD-RAM support) and are very popular.

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, compared to CD-R, DVD-R and DVD+R use different dyes 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, 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, which is key for writing 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.

1 Speed
2 Capacities
3 References
4 See also
5 External links

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Speed

Drive speed	Data rate		Disc write time	Equivalent CD rate	Reading speed
1x	11.08 Mbps	1.32 MB/s	53 min	9x	8x-18x
2x	22.16 Mbps	2.64 MB/s	27 min	18x	20x-24x
4x	44.32 Mbps	5.28 MB/s	14 min	36x	24x-32x
5x	55.40 Mbps	6.60 MB/s	11 min	45x	24x-32x
6x	66.48 Mbps	7.93 MB/s	9 min	54x	24x-32x
8x	88.64 Mbps	10.57 MB/s	7 min	72x	32x-40x
10x	110.80 Mbps	13.21 MB/s	6 min	90x	32x-40x
16x	177.28 Mbps	21.13 MB/s	4 min.	144x	32x-40x

Notes:

DVD 1x actual spin is 3 times that of CD 1x
Disk write time in table does not include overhead, leadout etc

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Capacities

A DVD advertised as 4.7 GB may seem to hold less than that because manufacturers quote the capacity of a writable DVD disc using decimal prefixes rather than the binary prefixes used by some software. This can be confusing. While a 4.7 GB DVD can store 4.7 billion bytes [4,700,000,000 bytes ÷ 1000 b/kB = 4,700,000 kB ÷ 1000 kB/MB = 4,700 MB ÷ 1000 MB/GB = 4.7 GB], using binary prefixes the same capacity is roughly 4.38 GiB [4,700,000,000 bytes ÷ 1024 b/KiB = 4,589,844 KiB ÷ 1024 KiB/MiB = 4,482.27 MiB ÷ 1024 MiB/GiB = 4.38 GiB]. [1]

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References

Bennett, Hugh. "In DVD's Own Image: DVD-R Technology and Promise." EMedia Professional July 1998: 30+
Bennett, Hugh. Understanding Recordable & Rewritable DVD. Cupertino: Optical Storage Technology Association, Apr. 2004. [2]

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