High Definition ( HD) DVD, formerly Advanced Optical Disc ( AOD), is one of several optical storage formats. The other formats competing with DVDs are the Blu-ray Disc( BD), Ultra Density Optical( UDO), Professional Disc for Data( PDD), and Enhanced Versatile Disc( EVD). All of these formats feature enormously high storage capacity and use blue laser light.
The HD-DVD, which retains the physical layer structure of the DVD, operates at a wavelength of 405 nm. Because of the relatively thick cover layer of 0.6 mm, the aperture could only be increased to 0.65. The aperture of the DVD is also increased to 0.65 nm. This short-wavelength light causes the pits and lands to be much smaller than on DVDs that use red lasers, resulting in lower track density and thus greater storage capacity. The focal point diameter is 0.31 µm.
In the case of HD-DVD, this means a storage capacity of 15 GB with a 1-layer coating, and 30 GB with a 2-layer coating. Toshiba also offers a three-layer version as HD- DVD-ROM with a storage capacity of 45 gigabytes (GB). The data rate is 15 Mbit/s.
The HD-DVD is ideal for storing high-definition television, HDTV. Codecs for video are H.264, MPEG-2 and MPEG-4, and Microsoft's WindowsMedia 9(WMV9). Audio codecs are Dolby Digital Plus( DD+), Digital Theatre Sound High Definition( DTS-HD) and MLP 2 mandatory.
For different HD-DVD versions there are already adopted specifications. So for the HD- DVD-RW, whose storage capacity for a single layer version was specified with 20 GB. For the HD- DVD-R this was specified with 15 GB and for the HD-DVD-ROM in single layer version with 15 GB, as dual layer with 30 GB and with triple layer 45 GB.
After Toshiba announced in January 2008 that they would not further develop HD-DVD, this should be the end of HD-DVD technology.