How DVDs work

A DVD-RW is a rewritable optical disc with equallabeled "DVD±RW", are very popular since there
storage capacity to a DVD-R, typically 4.7 GB. Theis not yet a single standard for recordable DVDs.
format was developed by Pioneer in November 1999There are a number of significant technical
and has been approved by the DVD Forum. Unlikedifferences between the "minus" (or often and
DVD-RAM, it is playable in about 75% of conventionalincorrectly "dash") format and the "plus" format,
DVD players.though most consumers would not notice the
The primary advantage of DVD-RW over DVD-R isdifference. One example is the ADIP system of
the ability to erase and rewrite to a DVD-RW disc.tracking and speed control being less susceptible to
According to Pioneer, DVD-RW discs may be writteninterference and error than the LPP system used by
to about 1,000 times before needing replacement,DVD-R, which makes the ADIP system more
making them comparable with the CD-RW standard.accurate at higher speeds. In addition, DVD+R(W)
DVD-RW discs are commonly used for volatile data,has a more robust error management system than
such as backups or collections of files. They are alsoDVD-R(W), allowing for more accurate burning to
increasingly used for home DVD video recorders. Onemedia independent of the quality of the media.
benefit to using a rewritable disc is if there areAdditional session linking methods are more accurate
writing errors when recording data, the disc is notwith DVD+R(W) versus DVD-R(W), resulting in
ruined and can still store data by erasing the faultyfewer damaged or unusable discs due to buffer
data.under-run and multi-session disks with fewer PI/PO
One competing rewritable format is DVD+RW. Hybriderrors.[citation needed]
drives that can handle both, often labeledLike other "plus" media, it is possible to use bitsetting
"DVD±RW", are very popular since there is notto increase the compatibility of DVD+R media.
yet a single standard for recordable DVDs.As of 2006, the market for recordable DVD
The recording layer in DVD-RW and DVD+RW is nottechnology shows little sign of settling down in favor
an organic dye, but a special phase change metalof either the "plus" or "minus" formats, which is
alloy, often GeSbTe. The alloy can be switched backmostly the result of the increasing numbers of
and forth between a crystalline phase and andual-format devices that can record to both formats;
amorphous phase, changing the reflectivity, dependingit has become very difficult to find new devices that
on the power of the laser beam. Data can thus becan only record to one of the formats. However,
written, erased and re-written.because the DVD-R format has been in use since
A DVD+R is a once-writable optical disc with 4.7 GB1997, it has had a five-year lead on DVD+R. As such,
(4.38 GiB) of storage capacity (more precisely,older or cheaper DVD players (up to 2004 vintage)
2295104 sectors of 2048 bytes each). The formatare more likely to favour the DVD-R standard
was developed by a coalition of corporations, knownexclusively, and when creating DVDs for distribution
as the DVD+RW Alliance, in mid 2002. Since the(where the playing unit is unknown or older) the
DVD+R format is a competing format to the DVD-RDVD-R format would normally be preferable.
format, which is developed by the DVD Forum, it hasDVD+R DL (DL stands for Double Layer), also called
not been approved by the DVD Forum, which claimsDVD+R9, is a derivative of the DVD+R format
that the DVD+R format is not an official DVDcreated by the DVD+RW Alliance. Its use was first
format.demonstrated in October 2003. DVD+R DL discs
In October of 2003, it was demonstrated that doubleemploy two recordable dye layers, each capable of
layer technology could be used with a DVD+R disc tostoring nearly the 4.7 GB capacity of a single-layer
nearly double the capacity to 8.5 GB per disc.disc, almost doubling the total disc capacity to 8.55
Manufacturers have incorporated this technology intoGB. Discs can be read in many DVD devices (older
commercial devices since mid-2004 (see DVD+R DL).units are less compatible) and can only be created
Unlike DVD+RW discs, DVD+R discs can only beusing DVD+R DL and Super Multi drives. DL drives
written to once. Because of this, DVD+R discs arestarted appearing on the market during mid 2004, at
suited to applications such as nonvolatile dataprices comparable to those of existing single-layer
storage, audio, or video. This can be very confusingdrives. However, the price of DL media ($1 to $5
because the DVD+RW Alliance logo is a stylizedUSD per disc) is many times that of single-layer
"RW" (See image, below). Thus, a DVD+R disc canmedia. The latest DL drives write double layer discs
have the RW logo, but it is not rewritable.slower (2.4x to 8x) than current single-layer media
The DVD+R format is divergent from the DVD-R(8x-16x).
format. Hybrid drives that can handle both, often