DVD and Blu-ray Glossary

DVD

DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than compact discs while having the same dimensions.

Pre-recorded DVDs are mass-produced using molding machines that physically stamp data onto the DVD. Such discs are known as DVD-ROM, because data can only be read and not written nor erased. Blank recordable DVDs (DVD-R and DVD+R) can be recorded once using a DVD recorder and then function as a DVD-ROM. Rewritable DVDs (DVD-RW, DVD+RW, and DVD-RAM) can be recorded and erased multiple times.

DVDs are used in DVD-Video consumer digital video format and in DVD-Audio consumer digital audio format, as well as for authoring AVCHD discs. DVDs containing other types of information may be referred to as DVD data discs.

DVD capacity and nomenclature

SS = single-sided, DS = double-sided, SL = single-layer, DL = dual-layer

Designation		Sides	Layers (total)	Diameter	Capacity
				(cm)	(GB)	(GiB)
DVD-5	SS SL	1	1	12	4.70	4.37
DVD-9	SS DL	1	2	12	8.54	7.95
DVD-10	DS SL	2	2	12	9.40	8.75
DVD-18	DS DL	2	4	12	17.08	15.90

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DVD-Video

DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in Asia, North America, Europe, and Australia.

DVD-R

DVD-R is a DVD recordable format. A DVD-R typically has a storage capacity of 4.71 GB.

Data on a DVD-R cannot be changed, whereas a DVD-RW (rewritable DVD) can be rewritten multiple (1000+) times.

DVD+R

DVD+R is a format for optical data storage. It is similar to, but incompatible with, the older DVD-R standard. A DVD+R is a write-once optical disc with 4.7 gigabytes (GB) of storage, generally used for non-volatile data storage or video applications.

DVD-RAM

DVD-RAM (DVD–Random Access Memory) is a disc specification presented in 1996 by the DVD Forum. DVD-RAM media have been used in computers as well as camcorders and personal video recorders since 1998.

DVD-RW

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.

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. From a business standpoint, the DVD+RW format was created largely in order to avoid paying royalties to the DVD Forum for the competing DVD-RW format. 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.

Blu-ray Disc

Blu-ray Disc (official abbreviation BD) is an optical disc storage medium designed to supersede the DVD format. The standard physical medium is a 12 cm plastic optical disc, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs (50 GB) the norm for feature-length video discs and additional layers possible in the future.

There are a few formats of Blu-ray Discs available or in the works including BD-ROM, BD-R and BD-RE. Although HD DVD has had combo discs (one side HD, other side standard DVD), Blu-ray has not yet created such a format, but is planning to introduce it soon.

Videos will be stored on either MPEG-2 (enhanced for new HD), MPEG-4/AVC (High Profile standard) or on the best of all three, VC-1 (HD standard based on Microsoft's Windows Media Video (WMV) technology.)

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BD+

BD+ is the name given to an experimental Digital Rights Management (DRM) mechanism that will be included on BD-ROM discs. The Blu-ray Disc Association was forced into providing this extra layer of protection following pressure from Fox. The HD DVD group did not agree to provide Fox with such a DRM over AACS. The fears about BD+ surround the possibility of studios like Fox theoretically being given the power to restrict Mandatory Managed Copy (a system that allows users to make digital copies of movies and send them around a home network).

BD+ allows for dynamic encryption schemes, meaning that if the protection were to be cracked, manufacturers could simply change the encryption scheme on new discs, so on single crack could not open up all BD-ROM discs. This is, of course a major advantage over the Content Scrambling System (CSS) protection used on DVD discs which was cracked years ago. All old and new DVDs containing CSS can be ripped from the disc to a HDD, or software is available to simply remove CSS on-the-fly.