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Digital
Versatile Discs
Formats
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 |
DVD-RAM
DVD-RW
DVD+RW
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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.
Compatibility
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
http://www.dvdrw.com
DVD Forum
http://www.dvdforum.org/forum.shtml
*The WAVE Report
is not responsible for content on additional sites
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