The format wars have begun , this time around the main contenders are blu-ray and HD  DVD , HD DVD has the backing of Microsoft and Toshiba among others , while Blu-Ray is being endorsed by the likes Sony and Poineer . To the average enthusiast the format itself means nothing , its what the format can deliver is what really matters .
There was once a time long(*100) ago when we used to see movies on VHS which used a Mylar tape running over a rotating head which itself ran at about 40 km/hr . How it works is a remarkable technological achievement and requires a few pages of information but the format in which the data is laid out is something like this


Dont bother about the image quality as Microsoft paint does not offer me much of a choice , well the red line and the green line are the control track and the Audio track and the diagonal lines represent the individual video tracks . the head reads this information and relays the information to the Television
Next came the digital media revolution ie. the CD and the DVD , The data is stored in microscopic pits and to the laser these pits look like small bumps , these bumps reflect the laser onto a lens which reads it as a series of ones and zeroes , this digital signal is sent to a DAC which converts it into an analog Signal and sends it to the display

A HD DVD is very similar to this but the pits are much smaller and the tracks are also very close together , another important difference is that DVD’s use Mpeg-2 format and HD-DVD’s primarily use Mpeg-4 compression( other formats are also supported). On the Hardware side the HD DVD reader uses a Blue -violet laser at 405nm wavelength as compared to a DVD which uses a red laser at 650 nm wavelength

The result of this is that an HD-DVD can on a single layer hold 15GB of data as compared to the DVD’s 4.7 GB further , the player itself can read the data and relay it to the display about three times faster that a DVD reader , all this increased data capacity enables a HD -DVD to deliver the 1125 lines of pixels ( from top to bottom) required for the signal to be classified as HD.

A very detailed technical description and heaps of information about HD-DVD can be found at the HD DVD promotion Website, those interested can visit the site , alternatively if you have a ge force 7 series and above video card ,you can download the nvidia pure video codec and some HD content and see what HD has to offer for yourself