Overview |
 Blu-ray, also known as Blu-ray Disc (BD), is the name of a next-generation optical disc format jointly developed by the Blu-ray Disc Association (BDA), a group of the world's leading consumer electronics, personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson). The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data. The format offers more than five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc. This extra capacity combined with the use of advanced video and audio codecs will offer consumers an unprecedented HD experience. |
Disc Structure |
 Laser and opticsLike its rival format HD DVD, Blu-ray uses a "blue" (technically blue-violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and infared lasers at 650 nm and 780 nm respectively.The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized 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, using a higher numerical aperture (0.85, compared with 0.6 for DVD), higher quality, dual-lens system, and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused much more tightly at the disk surface. This produces a smaller spot on the disc and allows more information to be physically contained in the same area. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding, allowing for even more data to be packed in. Hard-coating technologySince the Blu-ray data layer is closer to the surface of the disk, compared to the DVD standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for protection. Advances in polymer technology eventually made the caddies unnecessary.TDK was the first company to develop a working scratch protection coating for Blu-ray discs. It was named Durabis. 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. |
FAQ | ||||||||||||||||||||||||||||||||||||
What Blu-ray formats are planned?As with conventional CDs and DVDs, Blu-ray plans to provide a wide range of formats including ROM/R/RW. The following formats are part of the Blu-ray Disc specification: BD-ROM - read-only format for distribution of HD movies, games, software, etc. BD-R - recordable format for HD video recording and PC data storage. BD-RE - rewritable format for HD video recording and PC data storage. There's also plans for a BD/DVD hybrid format, which combines Blu-ray and DVD on the same disc so that it can be played in both Blu-ray players and DVD players. How much data can you fit on a Blu-ray disc?A single-layer disc can hold 25GB. A dual-layer disc can hold 50GB. To ensure that the Blu-ray Disc format is easily extendable (future-proof) it also includes support for multi-layer discs, which should allow the storage capacity to be increased to 100GB-200GB (25GB per layer) in the future simply by adding more layers to the discs. How much video can you fit on a Blu-ray disc?Over 9 hours of high-definition (HD) video on a 50GB disc. About 23 hours of standard-definition (SD) video on a 50GB disc. How fast can you read/write data on a Blu-ray disc?According to the Blu-ray Disc specification, 1x speed is defined as 36Mbps. However, as BD-ROM movies will require a 54Mbps data transfer rate the minimum speed we're expecting to see is 2x (72Mbps). Blu-ray also has the potential for much higher speeds, as a result of the larger numerical aperture (NA) adopted by Blu-ray Disc. The large NA value effectively means that Blu-ray will require less recording power and lower disc rotation speed than DVD and HD-DVD to achieve the same data transfer rate. While the media itself limited the recording speed in the past, the only limiting factor for Blu-ray is the capacity of the hardware. If we assume a maximum disc rotation speed of 10,000 RPM, then 12x at the outer diameter should be possible (about 400Mbps). This is why the Blu-ray Disc Association (BDA) already has plans to raise the speed to 8x (288Mbps) or more in the future. What video codecs will Blu-ray support?MPEG-2 - enhanced for HD, also used for playback of DVDs and HDTV recordings. MPEG-4 AVC - part of the MPEG-4 standard also known as H.264 (High Profile and Main Profile). SMPTE VC-1 - standard based on Microsoft's Windows Media Video (WMV) technology. Please note that this simply means that all Blu-ray players and recorders will have to support playback of these video codecs, it will still be up to the movie studios to decide which video codec(s) they use for their releases. Will Blu-ray support mandatory managed copy?Yes, mandatory managed copy (MMC) will be part of the Blu-ray format. This feature will enable consumers to make legal copies of their Blu-ray movies that can be transferred over a home network. Please note that "mandatory" refers to the movies having to offer this capability, while it will be up to each hardware manufacturer to decide if they want to support this feature. Will Blu-ray be backwards compatible with DVD?Yes, several leading consumer electronics companies (including Sony, Panasonic, Philips, Samsung, Pioneer, Sharp and LG) have already demonstrated products that can read/write CDs, DVDs and Blu-ray discs using a BD/DVD/CD compatible optical head, so you don't have to worry about your existing DVD collection becoming obsolete. In fact, most of the Blu-ray players coming out will support upscaling of DVDs to 1080p/1080i, so your existing DVD collection will look even better than before. While it's up to each manufacturer to decide if they want to make their products backwards compatible with DVD, the format is far too popular to not be supported. The Blu-ray Disc Association (BDA) expects every Blu-ray Disc device to be backward compatible with DVDs. What is the difference between Blu-ray and DVD?
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