Blu Ray - The Priciples
Blu-ray Discs (BDs) works on the same principles as regular DVDs, but by using more tightly compressed data, more information can be squeezed onto a disc.
The format is able to store and playback high-definition programming on today’s HD Ready TVs, at 720p, 1080i and 1080p (known as "Full HD") resolutions.
How it works
Blu-ray uses the same structure of "bumps" or "pits" as DVD and HD DVD. The BD disc is made of two 0.6mm discs sandwiched together.
Where the new discs differ is in the structure of the data layer. Blu-ray uses bumps that are less than half the size of those on a DVD, and which are even smaller than those used on HD DVD. This is because the recording layer on a Blu-ray Disc is just 0.1mm from the lacquer layer, as opposed to 0.6mm on an HD DVD. With the data layer being that much closer to the laser, less distortion is involved and greater density is possible.
Furthermore, tighter spacing between the data grooves on the disc (known as the "track pitch") from 0.4µm on an HD DVD to 0.32µm on Blu-ray (as compared to 0.74µm for regular DVD), allows still more data to be stored on a Blu-ray Disc – 25GB on a single-layered disc and 50GB on a dual-layered disc as opposed to 15GB/30GB on an HD DVD.
In order to read this tightly packed data, a blue-violet laser (usually just referred to as a blue laser) is employed. The red laser in a DVD player has a wavelength of 650nm, while that of a blue laser is just 405nm, meaning it can be more tightly focussed.
Blu-ray also has a data transfer speed that is superior to both DVD and HD DVD. A standard DVD can deliver up to 11.08Mbps (Megabits per second), while HD DVD can manage 36.55Mbps. Blu-ray has a bandwidth of up to 54Mbps, which is actually double the bandwidth of a high-definition broadcast.
The extra storage space on a Blu-ray Disc as compared to an HD DVD also means that high-definition programming can be encoded in MPEG-2. A single-layered BD can hold up to 135 minutes of MPEG-2 hi-def material as well as around two hours of standard-definition supplemental material. This is more than enough for most releases.
Blu-Ray Glossary
Blu-ray – A rival to HD DVD, offering more storage capacity but still delivering high-definition movies
DiVX – A video-compression format that can squeeze video files to a fraction of their normal space, allowing near-DVD quality movies to be downloaded from the internet and stored on a CD
HD DVD – A high-definition version of DVD technology
High-definition – A superior delivery format for TV that presents more lines of detail, resulting in a much sharper, more detailed image
Article from HomeCinemaUK.com
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