In this article, Guru3D explains how to use Multi-GPU with NVIDIA PhysX under Windows XP and Vista. There are 3 ways to use GeForce GPU with PhysX:
Standard – one GPU renders both graphics + PhysX (not ideal as you’ll need a lot of GPU horsepower).
SLI mode – have two GPUs render both graphics + PhysX (SLI motherboard required)
Multi-GPU mode – GPU1 renders graphics and GPU2 renders PhysX (SLI motherboard not required)
Now the trick to use Multi-GPU mode with Vista:
Now there’s a thing you will need to be aware of in the Multi GPU mode, it’s actually a Vista limitation but a second monitor must be attached to enable PhysX running on the second GeForce GPU. You must extend your Windows Vista desktop onto that monitor.
To bypass that issue, most monitors have a standard VGA and a DVI connector, right? Just use both. This limitation is related to the Windows Vista display driver model (WDDM). This limitation does not exist in Windows XP. In NVIDIA’s upcoming drivers, they will be offering a workaround to improve the experience for Windows Vista users.
With a single card or two cards in SLI mode you will not have this problem.
The PhysX Pack provided by NVIDIA contains a PhysX fluid demo:
The primary purpose of the NVIDIA PhysX Fluid Demo is to illustrate Smooth Particle Hydrodynamics (SPH)-based particle simulation technology accelerated by the NVIDIA GPU.
The pack also contains the Unreal Tournament III PhysX Mod:
The PhysX pack will be publicly available on August 12, 2008. The package consists of a new graphics driver that will enable PhysX on graphics cards equipped with GeForce 8, GeForce 9, and GeForce GTX GPUs, a downloadable PhysX software pack containing free Unreal Tournament 3 maps, the full version of NetDevil’s Warmonger, NVIDIA demos, and a first look at Object Software’s Metal Knight Zero and Nurien Software’s Nurien social-networking service.
FiringSquad takes a look at PhysX performance with GeForce 8/9/GTX200 based graphics cards by testing several games that support PhysX (Unreal Tournament, Warmonger, NKZ, Nurien). The first conclusion is that PhysX is really accelerated on GeForce and the difference between CPU PhysX and GPU PhysX is notable:
Futuremark has now decided to update its Hall of Fame to exclude all results using PhysX on a GPU, simply because this was not how they intended it to work.
With NVIDIA releasing their GeForce PhysX drivers, users of the PhysX accelerating GeForce cards were at an advantage over their Radeon counterparts, reason being that in a certain CPU test routine of the 3DMark Vantage benchmark, the physics processing abilities of the computer are tested, and since the physics API used happens to be PhysX, users of GeForce get higher scores despite not having a physics processor device such as an Ageia PhysX card. This differs from a real-life scenario where a GeForce accelerator does both graphics and physics and the overhead of physics processing affects the graphics processing abilities.