According to ATI's John Swiminer, the GPU (codenamed Hollywood) will not be based on any current PC architecture. There's even musings it may be a totally new design in comparison to it's cousin driving the Gamecube.

"It is designed the same as the Flipper was - from the ground up for a specific console. [It's a] totally different sort of architecture from what you might find on the PC. Certainly, there are some underlying values - you know, how you get graphics on the screen - that's there. It's not, for example, like we took a PC design and said 'oh, you know what? If we tweak this and test this, it will work in a console'."

The question still remains as to just how powerful the Revolution will be - and Swiminer didn't shed any more light on the issue, reiterating only that the focus of the design and the manufacturing of the Revolution is centred around gameplay and innovation rather than technical prowess and flash graphical functionality.