I didn’t care too much when the VHS/Betamax wars were going on because of my age. Today’s format war has gone into swing – HD-DVD/Blu-Ray (BD) will prove to be an interesting mix. Personally I would like BD to take the title, and not just because Microsoft supports HD-DVD! Both technologies are a step in the right direction of storing more information on a medium that consumers are comfortable with: the 12 cm diameter flat disc. The Blu-Ray folks have approched the problem with a revolution, not just an evolution, of the current media. Both systems use a 405nm blue-violet laser for reading/writing data, but the optics used in the BD system are of a higher quality and can focus the laser to a 0.60õm dot while HD-DVD is at a 0.76õm dot.à This allows a single-layer BD disc to hold up to 27GB of data!à Meanwhile, a single HD-DVD disc can hold 15GB of data.à For movies, this difference won’t mean much – since that much storage isn’t needed for HD versions of movies.à For storing data it’s an entirely different matter!

From the HD-DVD wikipedia article
Why haven’t we seend DVD’s with more than two layers?Ã I don’t know for sure, but my guess is because they are working with a legacy environment.Ã The DVD spec was created in the early 1990’s, with the dual-layer option added later.Ã The optics had to work in the 650nm and 780nm wavelength (for DVD’s and CD’s respectively), and the smaller dot size was largely an issue of focusing by moving the lens in closer to the disc (someone correct me if I’m wrong).
Both HD-DVD and BD have 2 lens systems, but because of BD’s superior optics, the focusing can be much more precise.Ã TDK showed a 100GB, four-layer BD disc which, as best I can tell, is possible thanks to the higher quality optics in the Blu-Ray system.Ã I think these kinds of advances will make Blu-Ray a better option for the large consumer base – not just movies, but computing too!
All of this was inspired by this article: ICv2 News – ‘Serenity’ First Universal Title on HD DVD
Of course, I REALLY hope these guys come out with a viable solution soon too. Ã Imagine 1.6TB with 120MB/s data rates from a 12cm disc!Ã Ahh holography – isn’t physics fun!