Third-generation optical discs

Major third-generation optical discs are designed for holding high-definition video, enabled by the use of short-wavelength visible light lasers (blue-violet for BluRay and HD-DVD, the most common formats so far).

Blu-ray is a new optical disc standard based on the use of a blue laser rather than the red laser of DVD players. The standard was developed collaboratively by Hitachi, LG, Matsushita (Panasonic), Pioneer, Philips, Samsung, Sharp, Sony, and Thomson. Toshiba and NEC are among the companies promoting a competitive optical format, HD-DVD.

The blue laser has a 405 nanometer (nm) wavelength that can focus more tightly than the red lasers used for writable DVD. As a consequence, a Blu-ray disc can store much more data in the same 12 centimeter space. Like the rewritable DVD formats, Blu-ray uses phase change technology to enable repeated writing to the disc.

Blu-ray's storage capacity is enough to store a continuous backup copy of most people's hard drives on a single disc. The first products have a 27 gigabyte (GB) single-sided capacity, 50 GB on dual-layer discs. Data streams at 36 megabytes per second. Single-sided Blu-ray discs can store up to 13 hours of standard video data, compared to single-sided DVD's 133 minutes.

Blu-ray disc players (BDPs) are available from a number of manufacturers, including Panasonic, Pioneer, Samsung and Sony. Sony's Playstation 3 also has a Blu-ray drive installed.

HD-DVD (high-density DVD) is a high capacity optical storage medium. A single-layer HD-DVD provides up to 15 gigabytes (GB) of storage capacity and the double-layer disc offers up to 30 GB. A standard single-sided, single-layer DVD offers 4.7 GB storage capacity.

A double-layer HD-DVD can contain up to 48 hours of standard-definition television programming. The data transfer rate of an HD-DVD drive is approximately 36 megabits per second (Mbps) -- more than sufficient to accommodate digital TV signals which are transmitted at 24 Mbps.

HD-DVD and Blu-ray are the two formats most often predicted to replace conventional DVD. A higher-capacity holographic storage medium called HVD (holographic versatile disc) is expected to reach the consumer market in 2008.

HD DVD/ Blu ray comparison

Blu-ray has a higher disc capacity per layer (25 GB vs 15 GB). However the majority (over 80%) of Blu-ray titles are in 25 GB single layer format while almost all (over 90%) HD DVD movies are in 30 GB dual layer format.

In terms of audio/video compression, HD DVD and Blu-ray are similar on the surface: both support MPEG-2, VC-1, and H.264 for video compression. Virtualy every HD DVD released uses an advanced codec (VC-1 or H.264) for video compression, reducing the required space for equivalent quality video. In terms of audio, there are many differences. With HD DVD support for the new Dolby Digital Plus audio codec is mandatory for HD DVD players, but optional for Blu-ray players. Furthermore HD DVD requires players must be able to decode the new lossless audio codec Dolby True HD, but this is optional for Blu-ray players.