Back in 1990, I was looking forward to when holographic storage was available on every desktop. Of course, that day's still not here, and I was wondering what had happened to it. Well, it hasn't gone away entirely, and there are companies still working on it. Via MIT's Technology Review (not available without a subscription, I'm afraid):
You could store a whole lot of stuff on a one-terabyte computer disc--say a million novels, 250,000 MP3 song files, or hundreds of full-length movies. A Lucent Technologies spin-off is hoping to bring you that kind of capacity using a long-talked-about technology: holographic storage, in which a laser records data in three dimensions on a polymer medium. The technology can store up to 300 times as much data as traditional optical drives of the same physical size, and the startup, Longmont, CO-based InPhase Technologies, says it will start selling the holographic drives next year.
Unfortunately, it's not yet rewritable, although InPhase hopes it will be in a couple of years. And even then commercial availability looks to be four years away, and these estimates tend to be optimistic. InPhase Technology has a website, and the explanation of how holographic storage works is here.