HD DVDs use the same blue laser
technology as Blu-ray Discs. This is why HD DVDs provide
more memory capacity than DVDs despite of its other
similarities.
The difference between Blu-ray and HD
DVD is the size of the aperture used on the optical pick-up
head inside drives and players. Blu-ray uses a 0.85 aperture
whereas HD DVDs only use a 0.65 aperture. Finally compare
that to current DVDs’ 0.6 aperture. The reason these are
different is because of the surface layer of the actual
discs. Their thickness limits the effectiveness of the laser
due to optical effects.
HD DVDs have a thickness of 0.6mm, the
same as current DVDs, which is why the aperture is only
marginally larger, thus limiting the discs capacity. BDs
have a surface that is only 0.1mm thick, which reduces
optical illusions, and enables the larger aperture to be
used.
Security
HD DVD-ROMs will include protection
which is expected to be produced by AACS LA. This
technology, called AACS, will also be included on BDs. AACS
is backed by companies supporting both Blu-ray and HD DVD
technologies. AACS uses similar security measures as CSS,
which failed in the past, thus raising concerns regarding
its effectiveness. The technology was in fact voted most
likely to fail by IEEE, the largest organization in the
world for ‘the advancement of technology related to
electricity’.
The difference between CSS and AACS is
that instead of having group decryption keys that were
allocated to a particular player model, every player will
have an individual ‘key’ used in a broadcast encryption
scheme. This allows licensors to identify individuals who
have leaked their keys. They can then disable a particular
player’s functionality with future media as well as carry
out legal action against a specific individual.
HD DVDs will also incorporate digital
watermarking to protect their products. Watermarking is a
process of hiding a copyright notice within digital media
that will prevent duplication or reproduction of media
without authorization.
Applications
HD DVDs will include the same
compression formats as BDs; MPEG-4 AVC, VC-1, and MPEG-2.
MPEG-2 TS has been used to allow direct recording from HDTV
broadcasts without picture quality loss. The current data
transfer rate is 36.55Mbps. It will of course be backwards
compatible with DVD and CD technology, this is where its
appeal lies, however that does not mean Blu-ray technology
is not backwards compatible.
The first lot of HD DVD players is
expected to arrive in March 2006. Microsoft did not include
a HD DVD player in their Xbox 360, but is said to be
releasing an external add-on drive late in 2006. There are
also many movie studios who will be releasing movies on both
HD DVD and BD formats by the end of this year.
