http://en.wikipedia.org/wiki/Blu-ray_dvdBlu-ray Disc is a 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 six times the size of a dual layer DVD at 8.5 GB.
Blu-ray was developed by the Blu-ray Disc Association, a group of leading companies representing consumer electronics, computer hardware, and motion picture production. The standard is covered by several patents belonging to different companies. As of March 2007, a joint licensing agreement for all the relevant patents had not yet been finalized.<1>
As of November 25, 2007, 415<2> titles had been released on Blu-ray Disc in the United States (32 of those titles have since been discontinued). As of October 9, 2007, 179 titles had been released in Japan, with 55 more titles planned for release.<3>
The Blu-ray standard is currently in a format war with its rival HD DVD, to determine which (if either) of the two formats will become the leading carrier for high-definition content to consumers.
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The primary rival to Blu-ray disc is HD DVD. Due to the format war, both sides are currently vying to promote their format as the best choice for studios and consumers. The technical details of each format do not differ much and should not affect the average consumer. Both formats are superior to DVD and produce quality HD video playback.
There is no Region Coding in the existing HD DVD specification; titles from any country can be played in any player. Some Blu-ray discs have Region Coding and will only play in players sold in the corresponding geographic region.
An estimated 1.97 million HD DVD discs have been sold between spring of 2006 and September 2007, compared to 3.01 million Blu-ray discs.<97> Sales of these two high-def disc formats accounted for only 2.5% of overall disc sales during the first half of 2007.<98>
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http://en.wikipedia.org/wiki/Comparison_of_high_definition_optical_disc_formats