"The Great thing about the Quad SLI PC that you see behind me is
it gives gamers kind of an idea of what the quality is gonna be like with the Playstation 3"

It's on http://www.gametrailers.com, Check the last minute of the Quad SLI interview.

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I guess the PS3's RSX is really powerful after all.
What do you guys think? Why is the RSX equivalent to four Graphics Card?

I personally think it's probably because it's a multi-core GPU, look here for RSX specification.