HD DVD or High-Definition DVD is a new format of optical data and video discs.
HD-DVD was designed to be the successor to the standard DVD format.
HD DVD disc can store 15 GB per layer instead of 4.7 GB per layer for the first generation of DVD discs.
Blu-Ray disc is a new generation of optical (laser) discs. Blu-ray name comes from the blue-violet laser used to read and write this type of disc.
Capacity of single-layer Blu-Ray disc is 25 gigabytes. A dual-layer Blu-ray Disc can store 50 GB of data.
Future technologies promise up to 12 layers on Blu-Ray disc.
