HD vs Blue ray
CD and DVD as data storage and delivery media, lasted successfully for decades and seems to be alive and kicking .As we speak, a new format war has begun, this time over the future of in-home media. On one side is HD-DVD, a format created by Toshiba and NEC; on the other side is Blu-Ray, created by Sony, Matsushita, and Philips.
A Blu-ray Disc (also called BD) is high-density optical disc format for the storage of digital information, including high-definition video.
The name Blu-ray Disc is derived from the blue-violet laser used to read and write this type of disc. Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser. A single layer Blu-ray Disc can store 25 gigabytes (GB), over five times the size of a single layer DVD at 4.7 GB. A dual layer Blu-ray Disc can store 50 GB, almost 6 times the size of a dual layer DVD at 8.5 GB
HD DVD is a high-density optical disc format designed for the storage of data and high-definition video. It is derived from the same underlying technologies. It can store about 3 1/2 times as much data as its predecessor.
HD DVD-ROM has a single-layer of 15 GB, a dual-layer capacity of 30 GB, and a 51 GB single-sided triple-layer disc. HD DVD-R and HD DVD-RW has a single-layer capacity of 15 GB, a dual-layer capacity of 30 GB. The HD DVD-RAM has a single-layer capacity of 20 GB. Like the original DVD format, the data layer of an HD DVD disc is 0.6 mm below the surface physically protecting the data layer from damage. The numerical aperture of the optical pick-up head is 0.65, compared with 0.6 for DVD. All HD DVD players are backward compatible with DVD and CD.
Both Blu-ray and HD-DVD use the same kind of 405 nanometer wavelength blue-violet laser. That means both can focus more sharply than the 650 nanometer red lasers used in current DVD players, and so both can store much more information on the same surface area of a disc.
But there are important differences between them.
Blu-ray packs data into a tighter single spiral on the surface of a disc than HD-DVD. That means a single disk can carry more digital "pits" - the tiny zeroes and ones that are translated into audio and digital content when a disc is played.
A standard double-layer DVD has 9 gigabytes (GB) capacity. HD-DVD is capable of holding 30GB of data - or a full-length high-definition movie, plus extras - on a double-layer disc, but Blu-ray launched with 50GB capacity.
It means that the two competing systems must use a different coating on their discs - HD-DVD uses a surface layer that is 0.6mm thick. Blu-ray's is much thinner at 0.1mm.
This is the root of what makes Blu-ray more expensive to produce - the thinner surface means standard DVD plants need to be re-tooled. A special hard coating must also be added to protect the information stored on a disc's surface.
Blu-ray is the more sophisticated format - and is being hailed as a "leapfrog" technology. That advance comes at a price, however.
The cheapest Blu-ray player weighs in at about €450 (€399 if you count Sony's PlayStation 3 console, which comes with Blu-ray on board). The cheapest HD-DVD player costs about €220 (or €110, if you count the add-on HD-DVD player for Microsoft's Xbox 360 games console - though to use it, you must already have bought an Xbox 360, which now retails from about €180).
