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Optical media types
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Standards
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A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R, typically 4.7 GB. The format was developed by Pioneer in November 1999 and has been approved by the DVD Forum. The smaller Mini DVD-RW holds 1.46 GB, with a diameter of 8 cm.
The primary advantage of DVD-RW over DVD-R is the ability to erase and rewrite to a DVD-RW disc. According to Pioneer, DVD-RW discs may be written to about 1,000 times before needing replacement. DVD-RW discs are commonly used to store data in a non-volatile format, such as when creating backups or collections of files. They are also increasingly used for home DVD video recorders. One benefit to using a rewritable disc is if there are writing errors when recording data, the disc is not ruined and can still store data by erasing the faulty data.
One competing rewritable format is DVD+RW. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular due to the lack of a single standard for recordable DVDs.
The recording layer in DVD-RW and DVD+RW is not an organic dye, but a special phase change metal alloy, often GeSbTe. The alloy can be switched back and forth between a crystalline phase and an amorphous phase, changing the reflectivity, depending on the power of the laser beam. Data can thus be written, erased and re-written.
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Drive Specifications [link]
Standard DVD-R/RW compatible drives use a 650nm red semiconductor laser diode. The average power consumption rating is 250mW to 400mW. Power consumption varies depending on the write speeds and dual layer support. Higher speed drives require more power for increased data throughput, and dual layer disks require more power to penetrate to the second layer of data.
Dual layer [link]
A specification for dual-layer DVD-RW discs with a capacity of 8.5 GB was approved by the DVD Forum.[1] However, manufacturing support for rewritable dual-layer discs did not materialize due to costs and expected competition from newer and higher-capacity formats like Blu-ray and HD DVD.
References [link]
- ^ DVD Specifications for Re-recordable Disc for Dual Layer (DVD-RW for DL) Physical Specifications, Version 2.0
External links [link]
- ISO/IEC 17342, 80 mm (1,46 Gbytes per side) and 120 mm (4,70 Gbytes per side) DVD re-recordable disk (DVD-RW)
- ISO/IEC 17342:2004 - publicly available standard
- Understanding Recordable & Rewritable DVD by Hugh Bennett
- DVD Forum
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DVD+RW
DVD+RW is a physical format for rewritable DVDs and can hold up to 4.7 GB. DVD+RW was created by the DVD+RW Alliance, an industry consortium of drive and disc manufacturers. Additionally, DVD+RW supports a method of writing called "lossless linking", which makes it suitable for random access and improves compatibility with DVD players.
DVD+RW must be formatted before recording by a DVD recorder.
The rewritable DVD+RW standard was formalized earlier than the non-rewritable DVD+R (the opposite was true with the DVD- formats). Although credit for developing the standard is often attributed to Philips, it was "finalized" in 1997 by the DVD+RW Alliance. It was then abandoned until 2001, when it was heavily revised (in particular, the capacity increased from 2.8 GB to 4.7GB).•
Technical details
The recording layer in DVD+RW and DVD-RW discs is a phase change metal alloy (often GeSbTe) whose crystalline phase and amorphous phase have different reflectivity. The states can be switched depending on the power of the writing laser, so data can be written, read, erased and re-written. DVD-R and DVD+R discs use an organic dye.
DVD±R
DVD±R (also DVD+/-R, or "DVD plus/dash R") is not a separate DVD format, but rather is a shorthand term for a DVD drive that can accept both of the common recordable DVD formats (i.e. DVD-R and DVD+R). Likewise, DVD±RW (also written as DVD±R/W, DVD±R/RW, DVD±R/±RW, DVD+/-RW, and other arbitrary ways) handles both common rewritable disc types (i.e. DVD-RW and DVD+RW, but not usually DVD-RAM).
