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Deregulation Smoke and Mirrors



Digital Versatile Discs


The Digital Versatile Disc (DVD) represents much more than just a better way to watch movies. With a storage capacity of 4.7 GB single-sided, and 9.4 GB double sided, the DVD represents a major step-up in affordable optical storage from the Compact Disc (CD), with its puny 650 MB capacity. Unfortunately, it also represents a step-up in format complexity. Compare the formats for each medium:

Application CD DVD
Pre-recorded consumer CD DVD Video
Pre-recorded PC CD-ROM DVD-ROM
Write-once, read many times CD-R DVD-R
Write many times, read many times CD-RW


Many people assume that physical similarities mean compatibility, but it's not always the case. Rewriteable discs such as CD-RW, in particular, will not play in all consumer players--limiting their usefulness to consumers. What good is a mix CD if your friend can't play it on her stereo? In some cases RW discs can only be played in the same type of drive that created them. This is acceptable when the discs are only used for data storage, and led to the development of the rewritable DVD standard, DVD-RAM. A data-centric solution, DVD-RAM takes advantage of the huge storage capacity of the discs, but is not playable in consumer players.

DVD-RW, another rewritable disc standard, does play in all consumer players, but does not act as a random-access data storage device as well as DVD-RAM. As digital cameras, PC-based editors, and DVD players grow in popularity, recording a DVD home video has become a realistic goal for many people. At the same time, PC users both professional and consumer will look to DVD's as a powerful way to store and back-up data. A rewritable DVD with full compatibility is needed. DVD+RW is a new rewritable DVD standard that solves the problem.


The burden of compatibility can either be placed on the writing device (called a DVD burner), or the reading device (a DVD player).

Placing the burden on the writing device indicates a manufacturer's burners will create discs that can be read by any DVD reader. The design goal is to produce rewriteable discs that are indistinguishable from pre-recorded, in a player. Because the disc itself is inert and can't change its properties, the only way to accomplish this is to ensure that the burner and discs conform to an established standard from the beginning of development. This way, the discs will play in any device that conforms to the same standard. In most cases that established standard is DVD Video.

Placing the burden on the reading device indicates a manufacturer's DVD players will be able to read discs conforming to multiple standards. In this case the machine itself will need to be able to detect and conform to multiple standards. The result is a more complex machine. The established base of DVD players will not be compatible to any new standards, either. This is a less-than-desirable situation for those in the consumer market.

Compatibility is a major technical challenge involving variables such as laser wavelength and media reflectivity. Because re-writable DVD's must be able to revert back to a blank state, they are physically very different from DVD's that can only be recorded once. By ensuring that the physical characteristics of the disc falls within the DVD Video standard, DVD+RW technology ensures compatibility across the installed base of players. The burden of compatibility is carried by the burner and disc, not the player.

DVD+RW versus DVD Multi

DVD Multi was created by the DVD Forum with the goal of universal compatibility. However, it is not a DVD format. DVD Multi is a logo--a system of certification that ensures a player can read all DVD formats. However, this places the burden on the player, leaving the installed base out of consideration. While this would achieve the same purpose as DVD+RW, it would most likely take longer, since it would be dependent on the rate at which users replaced their current DVD Video and DVD-ROM drives with DVD Multi drives. DVD+RW is also dependent on the same rate, but only in an authoring capacity. Once a DVD+RW is burned, any current DVD player could read it, no matter how old--an advantage over DVD Multi.

More info:

DVD+RW Alliance

DVD Forum

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Page updated 1/24/07
Copyright 4th Wave Inc, 2007