Home » DVD Replication: High Definition Blu-Ray & HD-DVD

DVD Replication: High Definition Blu-Ray & HD-DVD

(The following text is an edited extract from http://en.wikipedia.org/wiki/Dvd)

There were two plausible successors to DVD being developed by different consortia. Sony and Panasonic's Blu-ray Disc (BD) and DVD Forum's HD DVD; the "official" successor designed by Toshiba.

The two formats were engaged in a format war from 2006 to 2007, but in January and February, 2008, nearly all studios and large stores dropped support for HD DVD, and on February 19, Toshiba announced that they would discontinue the development of HD DVD. However, unlike previous format changes (i.e. vinyl records to compact disc, VHS videotape to DVD), there is no immediate indication that production of standard DVD will be immediately discontinued.

Both Blu-ray Disc and HD DVD players will play standard DVDs, and DVD release news websites such as TVShowsonDVD.com continue to list upcoming standard DVD releases well into 2009. In addition, in announcing its abandonment of HD DVD, Toshiba indicated it will still continue to produce standard DVD players and recorders.

Meanwhile, Wal-Mart, in announcing its decision to stop selling HD DVD in favour of Blu-ray Disc a few days before Toshiba's announcement, specifically singled out standard DVD in its announcement, indicating the mega-retailer has no plans to stop selling the older format as it adopts the new one.

Blu-Ray Laser and optics

Blu-ray Disc uses a "blue" (technically violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and near infrared 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, 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. 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

Because 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. The first discs were housed in cartridges for protection. Advances in polymer technology eventually made the cartridges unnecessary.

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 sprayed with a scratch-resistant and antistatic coating. Verbatim's recordable and rewritable Blu-ray Disc discs use their own proprietary hard-coat technology called ScratchGuard.