Specifics have been murky about how the Blu-ray Disc format can succeed DVD by enabling the recording of high-definition content. But the companies behind the format have recently tipped their hand to their strategy, including future enhancements.
DVDs don't have the storage capacity to accommodate an entire movie in high-definition format but Blu-ray Disc does. That's largely because it uses blue lasers to read and write data on the disc, rather than the red lasers used by DVD. A blue laser makes a smaller spot on the disc surface, which means the space required for one bit of data is smaller--and more data can be fit onto a 12-centimeter disc.
News source: PCWorld.com