The available discs in both formats are 1080p resolution, the highest HDTV format available, but you don’t necessary need a 1,080p resolution TV to get a great picture from either of these formats. Few people can honestly and consistently tell the difference between 1080p, 1080i or 720p, so it’s not as important as it seems.
The two standard DVD audio surround sound formats, Dolby Digital and DTS, have also been upgraded for the new disc formats. From Dolby Digital we get Dolby Digital Plus, which adds two more channels for a total of 7.1. Another format, Dolby TrueHD offers completely lossless 7.1 audio. DTS has also pumped its output to DTS-HD, also lossless up to 7.1 channels. Not all the players currently available will handle the new formats equally, but both HD DVD and Blu-ray also support standard Dolby Digital and DTS.
While the discs all look the same, they are very different. Standard definition DVDs can hold 4.7GBs of data on a single side in one layer. Double layer discs bump this up to 8.5GBs per side. HD DVD can hold 15GBs in one layer. Blu-ray can go to 25GBs per layer. Double-sided and multiple layer discs increase the capacity of both formats. All this capacity means more space for high bit rates and lots of extra features. While DVD uses a 650nm red laser to store movies, while the blue lasers used in both Blu-Ray and HD DVD are much finer (405nm), which allows them to write more information in the same amount of space.