Not tried it in the full game but in the demo you just turned it on in the launcher. Crippled the frame rate though, even on my 4870x2.
nVidia have stop PhysX working on a second card if the main one is an ATi in the latest drivers.
Not sure if PhysX in Batman still works with the old drivers though?
You can turn it on with any card, but if you're using ATI it'll do the calculations on your CPU and kill framerates.
http://www.rage3d.com/board/showthread.php?t=33953012Ok, so it's hard to see, but Task Manager is showing CPU utilization of 14%, which means the game—and Nvidia's purportedly multithreaded PhysX solver—is making use of just over one of our Core i7-965 Extreme's eight front-ends and less than one of its four cores. I'd say that in this situation, failing to make use of the CPU power available amounts to sabotaging performance on your competition's hardware. The truth is that rigid-body physics isn't too terribly hard to do on a modern CPU, even with lots of objects. Nvidia may not wish to port is PhysX solver to the Radeon, even though a GPU like Cypress is more than capable of handling the job. That's a shame, yet one can understand the business reasons. But if Nvidia is going to pay game developers to incorporate PhysX support into their games, it ought to work in good faith to optimize for the various processors available to it. At a very basic level, threading your easily parallelizable CPU-based PhysX solver should be part of that work, in my view.
Because a Core i7 is more than capable enough of handling PhysX by itself (this is what the tweak does). It allows ALL Cores to be used for PhysX (nVIDIA.. in an attempt to try and claim CPUs can't run PhysX... generally relegate it to a single core). In fact a Core i7 is nearly as powerful (GFLOP wise) in double precision mode as an nVIDIA GT200b Graphics card: http://www.realworldtech.com/page.cf...WT090909050230. A Nehalen Architecture based CPU is capable of around 102GFLOP in single precision (stock) and 55GFLOP is Double Precision while a GT200b based nVIDIA GPU can handle 622-933GFLOP in single precision and 77GFLOP in Double Precision. My understanding of PhysX is that it uses quite a lot of Double Precision calculations (to calculate physical interactions). So on that front they're quite close in performance. This also explains why enablong CPU PhysX (using the tweak) results in all of the PhysX effect while remaining playable.
I'm playing the game with PhysX turned on (since nvIDIA won't allow me to use the 9800GT anymore for dedicated PhysX) and it's entirely playable (I haven't seen it dip bellow 30FPS with ALL the PhysX candy turned on). To prove the point I will upload an HD video on YouTube... keep in mind I am ALSO recording while handling PhysX and the game.. so the CPU is under a lot of pressure yet does it all effortlessly.