Systems on a chip today reach ghz speeds, far beyond what the old consoles could do.
http://beagleboard.org/
But IBM processors and such (what the PS3 and 360 runs on, anyway) build upon people's expectations of getting exponentially better and more features added on.
I forget what it is, but there's some sort of chip-making law that maintains a theoretical limit on the amount of circuits or whatever on today's silicon-based doohickeys, so... organic computers in the future that you have to feed?
At this point, I'm just talking out of my ass, so what the fuck ever.
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