Hardware stats revealed at keynote address.
by Erik Brudvig 
Andrew Fitzgibbon, Principal Researcher for Microsoft Research, discussed the specifics. "What Natal does, is it evaluates effectively trillions of body configurations every frame. We've made it do that 30 times a second." This is done through a combination of software and a camera that tracks the body's motion in three dimensions.
Though Natal will evaluate the room 30 times a second, that does not necessarily mean that the games will also run at that rate. That will be the effective number of times the game can receive new input from the user, however.
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