DVD-R

DVD-R is a DVD recordable format. A DVD-R has a larger storage capacity than its optical predecessor, the 700 MB CD-R, typically storing 4.71 GB (or 4,488 MiB), 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. Data on a DVD-R cannot be changed, whereas a DVD-RW (DVD-rewritable) can be rewritten multiple (1000+) times. DVD-R(W) is one of three competing industry standard DVD recordable formats; the others are DVD+R(W) and DVD-RAM.

History

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

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 a red laser beam with a wavelength of 650 nm (for general use recordable DVD, versus a wavelength of 780 nm for CD-R) 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. The sandwich structure also helps protect the data containing layer from scratches by a thick "dummy" disk, a problem with CDs, which lack that structure. 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.

Competing formats

File:Appledvdr.jpg

A DVD-R jewel case

A previous DVD recordable format called DVD-RAM (DVD random access memory) predates DVD-R. Developed in 1996, DVD-RAM is a rewritable optical disc usually encased in a cartridge. Currently available in standard 4.7 GB, it is ideal for use that requires quick revisions and rewriting. In 2002 a new format was developed called DVD+R (or "plus" R). Created by a coalition called the DVD+RW Alliance, this format uses a number of improved technologies that, while generally unnoticeable to the end user, make a more reliable technology. One example is the ADIP system of tracking and speed control used by DVD+R being less susceptible to interference and error than the LPP system used by DVD-R, which makes the ADIP system more accurate at higher speeds. In addition, DVD+R(W) has a more robust error management system than DVD-R(W), allowing for more accurate burning to media independent of the quality of the media. Additional session linking methods are more accurate with DVD+R(W) versus DVD-R(W), resulting in fewer damaged or unusable discs due to buffer under-run and multi-session disks with fewer PI/PO errors.^[1]

This new format, among other things, resulted in DVD-R being unofficially referred to as DVD "minus" R (though in countries where British English is dominant, the term "minus R" was already common; not just in contrast to "plus R"). DVD-R and DVD+R technology is not directly compatible, which created a format war in the DVD technology industry. To reconcile the two competing formats, manufacturers created hybrid drives that could read both – most hybrid drives that handle both formats are labeled DVD±R and Super Multi (which includes DVD-RAM support) and are very popular.

As of 2006, the market for recordable DVD technology shows little sign of settling down in favour of either the plus or dash formats, which is mostly the result of the increasing numbers of dual-format devices that can record to both formats; it has become very difficult to find new devices that can only record to one of the formats. However, because the DVD-R format has been in use since 1997, it has had a five-year lead on DVD+R. As such, older or cheaper DVD players (up to 2004 vintage) are more likely to favour the DVD-R standard exclusively, and when creating DVDs for distribution (where the playing unit is unknown or older) the DVD-R format would normally be preferable.

Recordable DVD capacity comparison

For comparison, the table below shows storage capacities of the four most common DVD recordable media, excluding DVD-RAM. (SL) stands for standard single-layer discs, while DL denotes the double-layer variants. See articles on the formats in question for information on compatibility issues.

Disk Type	number of sectors for data (2,048 B each)	capacity in bytes	capacity in GB	capacity in GiB
DVD-R (SL)	2,298,496	4,707,319,808	4.7	4.384
DVD+R (SL)	2,295,104	4,700,372,992	4.7	4.378
DVD-R DL	4,171,712	8,543,666,176	8.5	7.957
DVD+R DL	4,173,824	8,547,991,552	8.5	7.961

References

^ http://adterrasperaspera.com/blog/2006/10/30/how-to-choose-cddvd-archival-media/

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. [1]

External links

Understanding Recordable & Rewritable DVD by Hugh Bennett
Pioneer Corporation
DVD Forum
Why DVD+R(W) is superior to DVD-R(W)
DVD-R Dual Layer First Look
Care and Handling of CDs and DVDs by Fred R. Byers
Standard ECMA-279 80 mm (1.23 GB per side) and 120 mm (3.95 GB per side) DVD-Recordable Disk (DVD-R)

[1] ttp://adterrasperaspera.com/blog/2006/10/30/how-to-choose-cddvd-archival-media/

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