The HD DVD Format
HD DVD is an optical disc storage technology which competed with Blu-ray in the post-DVD high-definition/high-storage market. Like Blu-ray, HD DVD uses a blue laser used instead of red to increase storage capacity.
HD DVD was backed by a group of manufacturers and content providers (led by Toshiba) calling themselves the DVD Forum. The DVD Forum decided upon HD DVD as their preferred format in 2003.
A single-layer HD DVD can hold 15GB of data, a dual-layer disc can hold 30GB. Prototypes have been demonstrated up to 45GB and the theoretical limit is 60GB. Although this is a big improvement over DVD, it is well short of Blu-ray's capacity.
Initially HD-DVD touted advantages over Blu-ray such as being fully backwards-compatible and cheaper to produce, although the compatibility issue was quickly countered by Blu-ray. See HD DVD vs Blu-ray for more information.
Toshiba announced an end to its HD-DVD production in February 2008, effectively ending the format war.