Toshiba HD DVD
The need for a higher-capacity, high-resolution video disc format was recognized by both Sony Corporation and Toshiba. Sony came up with the Blu-ray format, while Toshiba (in concert with NEC) developed the HD DVD format. These two formats, however, are incompatible with each other -- and, in fact, are competing in the marketplace.
Despite their incompatibilities, the two formats have a lot in common. For example, both HD DVD and Blu-ray discs are the same thickness as standard DVD discs. HD DVD even uses similar construction to today's discs, with a data layer is sandwiched between two polycarbonate layers. (This common construction enables HD DVD to be backwards compatible with today's DVD discs; a single player can play both HD DVDs and standard DVDs.) The extra capacity in the HD DVD format comes from smaller pits in the data layer; with HD DVD, the pits are just 0.15 microns long, about half the size as those on a standard DVD.
A Blu-ray disc has the same 1.2mm thickness, but the construction is much different. A Blu-ray disc places the data layer on the very bottom of the disc, with a thick protective polycarbonate layer on top. This puts the data closer to the laser beam during playback, which allows for more pits to be encoded on the data layer. It also makes for a more difficult production process; manufacturers have to invest heavily in new equipment to create Blu-ray discs, where HD DVD discs can be produced in current DVD manufacturing plants with less new investment.
Both Blu-ray and HD DVD players utilize blue lasers, which have a shorter wavelength than the red lasers used in traditional DVD players. The smaller blue beam can focus more precisely than the older red beam, enabling it to read information in either format's smaller pits.
The end result is that both Blu-ray and HD DVD discs can handle high-definition video in either 1080i or 1080p resolution. In addition, both formats deliver higher-quality digital audio than you get with current DVDs, via the new Dolby Digital Plus, Dolby Digital TrueHD, and DTS HD high-bitrate surround sound formats.
Michael Miller is a writer and commentator on technology and digital lifestyle topics. 
