Asus PhysX P1

The CPU is massively overloaded when running a game, furiously calculating everything from artificial character intelligence to accurate physics modelling, as well as deciding what you need to be seeing of the current level. Just like a GPU, a PPU (physics processing unit) aims to take some of this load, while also producing better effects than the CPU is capable of. Naturally, comparisons have been made between the all-new AGEIA PhysX PPU and the Voodoo 1 GPU released toward the end of 1996. The trouble is that the benefits of hardware-accelerated graphics are easily shown, whereas hardware physics acceleration is a much harder sell.

AGEIA sees the PhysX chip as delivering "Advanced Gaming Physics", which it defines along four criteria: fidelity, scale, interaction and sophistication. Roughly speaking, that covers the accuracy of physics modelling and the size, type and number of objects modelled. While a CPU is able to model a box falling or cloth waving in the wind, AGEIA's selling pitch is that the P1 will be able to handle many more such effects than a CPU could - and more effectively - and so will dramatically improve the perception of realism.

The problem is that a CPU isn't massively parallel, has a relatively short pipeline and isn't ideal at calculating many high-precision 32-bit floating point operations. However, a GPU is exactly that and, when AGEIA announced the PhysX chip roughly six months ago, speculation was rife that it was just a tweaked GPU using a different API. This seems to have made AGEIA very circumspect about disclosing the details of the PhysX chip, with its accompanying white paper light on details. All we could wring out of AGEIA was that the PhysX chip is "a massively parallel interactive physics engine" with "multiple processing cores".

The lack of any detail into exactly how many cores it has, and how a recent start-up company has apparently managed to beat Intel and AMD to the public demonstration of multicore technology, makes us question the difference between a GPU pipeline and "physics processing core" on the PhysX chip. Six months ago, strong rumours gave the PhysX chip eight pipelines with no mention of a multicore design.

AGEIA still goes to great lengths to differentiate PhysX from a GPU, although it only gives one concrete figure: an internal bandwidth of nearly 2TB/sec. That's not such an important figure, though, so is never quoted by graphics chip manufacturers and thus there's no comparison to be made. Nonetheless, AGEIA claims that GPUs have significantly less internal bandwidth and so aren't capable of modelling as many physics-based effects. Then again, we've seen good physics-based effects performed in pixel shaders on GPUs, such as the smoke and fog effects in Call of Duty 2.

Further reasons given by AGEIA that a GPU isn't up to the job include difficulty parallelising some physics calculations, and the fact that a GPU's pipelines aren't optimised for physics. These arguments seem to be slightly spurious, however, as Nvidia recently demonstrated physics hardware acceleration on two GPUs in SLI using the new Havok FX API. Search for "SLI Physics" on www.nvidia.com to read more.

That Nvidia is developing hardware physics acceleration can only be good news for AGEIA, though, as it shows that at least one other major company sees the need for it. And AGEIA has been successful in signing developers up to its API (which is, tellingly, incompatible with the Havok FX of SLI Physics). Bundled with this Asus card is Ghost Recon: Advanced Warfighter, which requires the PhysX driver regardless of whether there's a card installed. This smacks of a last-minute addition and indeed we saw little difference between using the PhysX card and not. Some extra debris was added to explosions but, disappointingly, it all disappears within seconds. We also saw frame rates drop by a few fps. Among other currently or soon-to-be available games are Rise of Nations: Rise of Legends, Bet on Soldier: Blood Sport and - most interestingly - Unreal Tournament 2007.