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A 12 cm Sony DVD+RW shown in comparison in size to a 7.5 inch Dixon Ticonderoga pencil.

DVD+RW is the name a standard for optical discs: one of several types of DVD, which hold up to about 4.7GB per disc and are used for storing films, music or other data.

Summary of DVDs

DVDs are read by a red laser beam which bounces off the spinning surface of the disc and is read by a sensor which interprets each location as a binary digit depending on whether it is reflective or not. How the reflectivity of each spot is altered depends on the type of disc: in read-only discs, for instance, a physical indentation (pit) is made; in some others an organic dye changes color; in DVD+RW discs a metal compound changes phase.

DVDs are the same size as the earlier optical discs called CDs (Compact Discs) but hold about up to about 5 times as much data. CDs were developed to hold an "album" of music (ie to replace the LP). DVDs were developed primarily as a successor to VHS tapes — as a medium for selling (and, later, recording) TV programs and films.

DVD format names

"DVD" originally stood for Digital Video Disc until their potential for storing other data was recognized in the re-branding as "Digital Versatile Discs". The most basic type is simply called "DVD". It is (to the consumer) read-only, and these are the discs on which commercial recordings are distributed.

All other types of DVD are all to some extent "writeable", and various extra symbols are used after "DVD" to distinguish them. The two main groups are indicated by either a plus or minus sign. This symbol is followed by either be an "R" or "RW". "R" means "Recordable": the consumer can record to a blank disc once only (to back up a data store, or a precious home movie, for example). "RW" means Rewritable: the consumer can overwrite the information (up to about 1000 times). Any of these four basic types (DVD+R, DVD-R, DVD+RW, DVD-RW) may take the suffix "DL" (Double Layer) to indicate an approximately double-density disc which stores data at two different layers (depths). A completely different type of DVD is called DVD-RAM to indicate its potential similarity of use to that of solid-state memory chips.

DVD+RW

DVD+RW (and DVD+R) discs store about 4.7 GB of data (interpreted as ? 4.7 · 10⁹, actually 2295104 sectors of 2048 bytes each).

DVD+RW supports random write access, which means that data can be added and removed without erasing the whole disc and starting over (up to about 1000 times). DVD+RWs can thus be treated like removable hard disks making them comparable with the CD-RW standard. (In contrast, DVD-RW discs must be erased before re-writing can take place).

DVD+RW was primarily developed for holding discrete data sets (which change with time) or as recyclable discs for backing up collections of files. However, they (and DVD-RW) are less popular for computer use than DVD-R or DVD+R discs, because they are not suitable for permanent backup files (because of security considerations and because mail order or bulk pricing of non-rewritable media is significantly cheaper). For similar reasons, rewritable discs are not as widely used for permanent storage of home DVD video recorders as DVD-R and DVD+R.

On the other hand, DVD+RW or DVD-RW make an inexpensive medium for multiple temporary recordings: they can be used for the daily discs of a backup cycle (which are overwritten after a number of days or weeks), and became very popular for their convenience and cheapness as a medium for time-shifting TV (recording programs for a single later viewing and erasing), DVD+RW discs are now playable in three quarters of today's DVD players, many of them Hybrid (DVD±RW) drives.

Windows XP can read DVDs and can burn recordable discs; but it cannot burn rewritable DVDs without add-on software. However, most new and upgraded PCs have a drive (and software) which can read and write all formats, except DVD-RAM, which fewer people use at the moment.

All rewritables (DVD+RW, DVD-RW, and DVD-RAM) can be burned natively from the Windows Vista and Mac OS X operating systems, and the GNOME and KDE desktop environments (the latter using K3b).

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).

History of the DVD+RW standard

The rewritable DVD+RW standard was formalized earlier than the non-rewritable relation DVD+R (the opposite was true with the DVD- formats). Although credit for developing the standard is often attributed unilaterally to Philips, it was "finalized" in 1997 by a coalition of corporations known as 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 5GB) and commercial products started to arrive (initially, only cheaper and "no-name" recorders) even though the standard was not approved by the DVD Forum (which produced a competing standard, DVD-RW)

However, the "random" rewriting made the DVD+RW format popular. Originally, the branded manufacturers except Philips only made pure DVD-RW recorders and players, but they could not ignore consumer preferences indefinitely.

External links

Understanding Recordable & Rewritable DVD by Hugh Bennett
DVD+RW Alliance

This computer-storage-related article is a stub. You can help Wikipedia by expanding it.

@@ Line 19: / Line 19: @@
 DVD+RW (and DVD+R) discs store about 4.7 [[gigabyte|GB]] of data (interpreted as ? 4.7 · 10<sup>9</sup>, actually 2295104 sectors of 2048 [[byte]]s each).
-DVD+RW supports [[random access|random]] write access, which means that data can be added and removed without erasing the whole disc and starting over (up to about 1000 times). DVD+RWs can thus be treated like removable hard disks* making them comparable with the [[CD-RW]] standard. (In contrast, DVD-RW discs must be erased before re-writing can take place).
+DVD+RW supports [[random access|random]] write access, which means that data can be added and removed without erasing the whole disc and starting over (up to about 1000 times). DVD+RWs can thus be treated like removable hard disks making them comparable with the [[CD-RW]] standard. (In contrast, DVD-RW discs must be erased before re-writing can take place).
-''* Note: You must use burning software to erase, edit, or add data, unlike a removable hard disk.''
 DVD+RW was primarily developed for holding discrete data sets (which change with time) or as recyclable discs for backing up collections of files.  However, they (and DVD-RW) are less popular for computer use than [[DVD-R]] or [[DVD+R]] discs, because they are not suitable for permanent backup files (because of security considerations and because mail order or bulk pricing of non-rewritable media is significantly cheaper).  For similar reasons, rewritable discs are not as widely used for permanent storage of home DVD [[video recorder]]s as [[DVD-R]] and [[DVD+R]].