2 GPUs
Regarding the dual gpu quesion from Kenny Millar, they're getting ready fro the next version (Snow Leopard). Specifically, the OpenCL functioanlity http://www.apple.com/macosx/snowleopard/ check the botom of thep page.
Do a search around WPA being rendered obsolete when using GPU's to accelrate the brute forceing attempt to get n idea of the impact of the general availability of general GPU acceleration will bring...
eventually.
Reqwrites will bbe necessary.
OpenCL is open source so will be availabe on Linux and Windows. also. I'm looking forward to it.
http://en.wikipedia.org/wiki/OpenCL
Biting the hand that feeds IT
