The DVD boasts substantially
higher density recording when compared with previous types of optical
discs. The width of the grooves and size of the pits formed on the
disc substrate are considerably narrower and smaller. Moreover the
thickness of the DVD substrate, at O.6mm, is half that of the 1.2mm
used for CDs.
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For the DVD to realise its high recording density, it uses a red
laser with a shorter wavelength than that of CD-R. Compared with
CD-R and CD-RW, with their wavelength recording of 780nm, the DVDs
wavelength is shorter, from 635 to 650nm. When the next generation
DVD, with a 15GB capacity or greater is realised in the near future,
it will make use of a blue laser with an even shorter wavelength
(in the 400nm range).
‘The DVD Forum’ sets the standards for DVD technologies
and has endorsed 3 different recordable DVD formats; DVD-RAM, DVD-R
- Panasonic, Toshiba and Hitachi are backing DVD-RAM.
- Pioneer is the corporate force behind DVD-R and its rewritable
- A fourth format, DVD+RW, is backed by Philips, Sony, HP, Ricoh
and Yamaha, but has not yet been approved by the Forum.
The three different flavours of recordable DVD trying to become
the digital home video format of the future are DVD-RAM, DVD-RW
and DVD +RW
Each has approximately the same recording time using Mpeg compression
- between two hours at DVD quality and five hours at VHS quality
– and can all be re-recorded up to 100,000 times.
However, they are not interchangeable, so the chances are only
one will survive as a domestic format. Just which one that will
be is still wide open.
The main roadblock to arriving at a single DVD recordable format
has been DVD-Video/DVD ROM cross-platform compatibility.
What is the difference between DVD-ROM, DVD-Video, DVD-RAM, DVD-R,
DVD-RW and DVD+RW?
DVD-ROM is a play-only optical disc similar to today’s CD-ROM.
The DVD-ROM has a much higher storage capacity (4.7Gbytes per side).
DVD-Video is a play-only disc that will hold a full length feature
film. The DVD-Video will hold 135 minutes of high quality video
and will add extra’s like multi-language support, subtitles
and even interactivity. The DVD-Video quality is higher than laser
discs and VHS. DVD-Video titles can be played in DVD players and
computers with DVD-ROM players and MPEG2 decoder boards.
DVD-RAM is a rewritable version of DVD. Panasonic launched DVD-RAM
to the PC market over two years ago but the lack of domestic DVD-RAM
video machines has meant that its first mover advantage has been
lost. The recordable disc is held within a caddy - this protects
the media from dust contamination but means the discs will not work
with existing DVD players. It uses a phase-change recording principle.
TDK has developed a new type of phase change recording material
called AVIST (Advanced & Versatile Information Storage Technology).
It is expected that major DVD-ROM drive manufacturers will soon
release DVD-RAM readable DVD-ROM drives, which have a standard tray
DVD-R is a write-once recordable version of DVD. It uses an improved
cyanine dye, similar to the material used in CD-R. DVD-R can be
used for both DVD-ROM and DVD-Video applications.
DVD-RW: Pioneer’s DVD-RW format is a naked disc that has
been developed from CD-RW technology using a phase changing dye
between disc layers. Thanks to AVIST, TDK has already completed
development work on a phase-change layer that is ideal for the DVD-RW
format. Although current DVD players will not replay DVD-RW discs,
next generation players may well do as the format has the backing
of the DVD Forum in Japan. The first domestic recordable DVD players
to market (early this year) are likely to be DVD-RW.
DVD+RW: Developed by Sony, Philips and Hewlett-Packard, DVD+RW
is another naked disc format but has the advantage of being more
compatible with existing DVD drives. DVD+RW promises full backward
compatibility with existing DVD-ROM drives and DVD-Video players.
However, the DVD Forum does not sanction this format as yet –
this will delay compatible players coming to market, but both Sony
and Philips are active members of the Forum.
What is the difference between Type I, Type II and Type III DVD-RAM?
Basically, Type II DVD-RAM has a hinged slot on the cartridge to
allow removal of the disc inside – Type I does not (the disc
is housed in a sealed cartridge).
Therefore Type II has the advantage of being able to use the media
in jukeboxes type applications (nb. Disc cannot then be put back
The latest version, Type III, is a bare disc that is placed in
an ‘open cartridge’ for recording.
CURRENT TDK DVD MEDIA LINE-UP-
DVD-RAM 2.6GB – Single-sided Type II
DVD-RAM 5.2GB – Double-sided Type I
DVD-RAM 4.7GB – Single-sided Type II
DVD-R47S (General purpose)
The last 2 items, DVD-R47S and DVD-R47SV20 are new and available
DVD-R47S is 100% compatible with Pioneer’s DVR-301 and Panasonic’s
SW-9501 recorders. Both recorders are compatible with the DVD-R
for GENERAL USE V1.0 spec.
DVD-R47SV20 can only be used on the Pioneer DVR-201s. Fully compatible
with the DVD-R for AUTHORING v2.0 standard. Target customers for
this item are professional authoring houses, document archival systems,
DVD replicators etc.
Both media types are NOT interchangeable.
(DVD-R395 will also only work in the Pioneer DVR-S201)
Future products include;
DVD-RAM 9.4GB – Double-sided Type I