Blu-ray Disc
A Blu-ray Disc (also called BD) is a high-density optical disc format for the storage of digital media, 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 Blu-ray Disc can store 25 GB on each layer, as opposed to a DVD's 4.7 GB.Blu-ray Disc is similar to PDD, another optical disc format developed by Sony (which has been available since 2004) but offering higher data transfer speeds. PDD was not intended for home video use and was aimed at business data archiving and backup.Blu-ray Disc is currently in a "format war" with rival format HD DVD.The Blu-ray Disc system uses a blue-violet laser operating at a wavelength of 405 nm, similar to the one used for HD DVD, to read and write data. Conventional DVDs and CDs use red and infrared lasers at 650 nm and 780 nm respectively.
Because the Blu-ray Disc standard places the data recording layer close to the surface of the disc, early discs were susceptible to contamination and scratches and had to be enclosed in plastic caddies for protection. The consortium worried that such an inconvenience would hurt Blu-ray Disc's market adoption. Blu-ray Discs now use a layer of protective material on the surface through which the data is read.
The recent introduction of a clear polymer coating has given Blu-ray Discs substantial scratch resistance. The coating is developed by TDK and is called "Durabis". It allows BDs to be cleaned safely with only a tissue. The coating is said to successfully resist "wire wool scrubbing" according to Samsung Optical technical manager Chas Kalsi. It is not clear, however, whether discs will use the Durabis coating as standard or only in premium discs.
Both Sony and Panasonic replication methods include proprietary hard-coat technologies. Sony's rewritable media are sprayed with a scratch-resistant and antistatic coating. Verbatim recordable and rewritable Blu-ray Disc discs use their own proprietary hard-coat technology called ScratchGuard.
Although the Blu-ray Disc specification has been finalized, engineers continue working to advance the technology. Quad-layer (100 GB) discs have been demonstrated on a drive with modified optics. Furthermore TDK announced in August 2006 that they have created a working experimental Blu-ray Disc capable of holding 200 GB of data on a single side, using six 33 GB data layers.Such discs would almost certainly not work on some of today's Blu-ray Disc players, as these devices are only designed and tested on discs that meet the current specification.
