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Blu-ray Disc
Blu-ray Disc (also known as BD or Blu-Ray) is an optical disc storage medium designed to supersede the standard DVD format.
Its main uses are for storing high-definition video, PlayStation 3 video games, and other data, with up to 25 GB per single layered, and 50 GB per dual layered disc. Although these numbers represent the standard storage for Blu-Ray drives, the specification is open-ended, with the upper theoretical storage limit left unclear. 200 GB discs are available, and 100 GB discs are readable without extra equipment or modified firmware.[3] The disc has the same physical dimensions as standard DVDs and CDs.
The name Blu-ray Disc derives from the blue-violet laser used to read the disc. While a standard DVD uses a 650 nanometer red laser, Blu-ray uses a shorter wavelength, a 405 nm blue-violet laser, and allows for almost ten times more data storage than a DVD.
During the format war over high-definition optical discs, Blu-ray competed with the HD DVD format. Toshiba, the main company supporting HD DVD, conceded in February 2008, and the format war ended;[4] In late 2009, Toshiba released its own Blu-ray Disc player.[5]
Blu-ray Disc was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. As of June 2009, more than 1,500 Blu-ray disc titles are available in Australia and the United Kingdom, with 2,500 in Japan, the United States and Canada
History
A blank rewritable Blu-ray Disc (BD-RE).
Commercial HDTV sets began to appear in the consumer market around 1998, but there was no commonly accepted, inexpensive way to record or play HD content. In fact, there was no medium with the storage required to accommodate HD codecs, except for JVC's Digital VHS and Sony's HDCAM.[8] Nevertheless, it was well known that using lasers with shorter wavelengths would enable optical storage with higher density. Shuji Nakamura invented the practical blue laser diode; it was a sensation among the computer storage-medium community, although a lengthy patent lawsuit delayed commercial introduction
Reverse side of a Blu-ray Disc
Media type High-density optical disc
Encoding MPEG-2, H.264/MPEG-4 AVC, and VC-1
Capacity 25 to 50 GB (single-layer)
50 to 100 GB (dual-layer)
Block size 64kb ECC
Read mechanism 400 nm laser:
1× @ 36 Mbit/s (4.5 MByte/s)2× @ 72 Mbit/s (9 MByte/s)
4× @ 144 Mbit/s (18 MByte/s)
6× @ 216 Mbit/s[1] (27 MByte/s)
8× @ 288 Mbit/s (36 MByte/s)
12× @ 432 Mbit/s (54 MByte/s)
Developed by Blu-ray Disc Association[2]Usage Data storage1080p High-definition video
High-definition audio 3D steroscopic Quad HD 2160p
future possibility Ultra HD
Laser and optics
Blu-ray Disc uses a "blue" (technically violet) laser, operating at a wavelength of 405 nm, to read and write data. The diodes are InGaN (Indium Gallium Nitride) lasers that produce 405 nm photons directly, that is, without frequency doubling or other nonlinear optical mechanisms. Conventional DVDs and CDs use red and near-infrared lasers, at 650 nm and 780 nm, respectively.
Panasonic Internal Blu-ray ROM notebook drive. Ships with select Sony VAIO notebooks
The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD-size disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85, and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. For Blu-ray Disc, the spot size is 580 nm. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the capacity. (See Compact Disc for information on optical discs' physical structure.)
Hard-coating technology
Since the Blu-ray Disc data layer is closer to the surface of the disc compared to the DVD standard, it was at first more vulnerable to scratches.[58] The first discs were housed in cartridges for protection, resembling Professional Discs introduced by Sony in 2003.
Using a cartridge would increase the price of an already expensive medium, so hard-coating of the pickup surface was chosen instead. TDK was the first company to develop a working scratch-protection coating for Blu-ray Discs. It was named Durabis. In addition, both Sony and Panasonic's replication methods include proprietary hard-coat technologies. Sony's rewritable media are spin-coated, using a scratch-resistant and antistatic coating. Verbatim's recordable and rewritable Blu-ray Discs use their own proprietary hard-coat technology, called ScratchGuard.
All Blu-Ray Disc media are required by specification to be scratch-resistant.[59] DVD media are not required to be scratch-resistant, but since development of the technology, some companies, such as Verbatim, implemented hard-coating for more expensive lineups of recordable DVDs.
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