writes "What do you do when you're getting close to the limits of 2-dimensional optical technology? Well, how many dimensions do we have to work with?"
From the Ars Technica article: "How much greater data density? In the Hitachi Maxell device, a single disc about 1 cm larger in diameter than a CD will buy you 300GB. By way of contrast, HD-DVD currently offers a maximum of 30GB on a 2-layer disc, and Blu-ray tops out at 50GB. Although upgrades are in the works that promise to increase the capacity of both of those formats, even the most pie-in-the-sky predictions fall short of what is planned for merely the first commercial generation of holographic storage. Future plans for that medium include boosting the capacity to 800GB in two years, and 1.6TB per disc by 2010."