HD-DVD (high-density DVD) is a high capacity optical storagemedium. 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.
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A double-layer HD-DVD can contain up to eight hours of 1125-line high-density television (HDTV) programming or 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 stores more data by:
- Using lasers with shorter wavelength: 405 nanometers (nm) in the visible blue range for HD-DVD compared with 650 nm in the visible red range for conventional DVD.
- Employing a more sophisticated data compression: An HD-DVD player can reproduce data from disks that use either the MPEG-2 standard or the more robust MPEG-4 AVC and VC-1 compression standards.
- Spacing tracks more closely together. A conventional DVD has a track pitch (spacing) of 0.75 micrometers, while HD-DVD uses a track pitch of0.40 micrometers.
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.