You see, the physics card is somewhat like a preparation tool. It takes the event that will shortly be produced on the screen and does all the calculations that will increase the fidelity, scale, interaction, and sophistication of the scene, as stated above. That, however, is the limit of the PPU’s involvement. The PPU does not aid in the visual production of the event on the screen; that is a task that is still handled 100% by the video card. Think of it like this: the physics card has just created a far more realistic explosion, but the video card still has to render all of those extra particles. The end result is a much more believable visual effect, at the cost of system performance due to the increased graphics load.

To view videos of the explosions with and without the PhysX effects, download the following file: shoes_physx_grawvideos.zip (17.3MB, .wmv)

It is a tradeoff then; a more realistic visual effect for a significant drop in FPS. This, again, might seem counter-intuitive. Why not just crank up the visual effects in the game and lose the same amount of FPS and save yourself the cost of a roughly $250 ASUS PhysX P1 card? Well, the fact of the matter is that cranking up the visual effects in the game will result in added video card load, and that load will be generated by enhanced texture detail, shading, and shadows – no physics. If there was an option to increase game physics, the reality is that the impending drop in performance due to increased CPU load would likely cause a larger FPS drop than we have witnessed here with the PhysX card.

Curious as to exactly what amount of work is being offloaded from the CPU to the PhysX card, we ran a performance monitor log during these scenes as well. The results of these tests indicated an insignificant difference in terms of CPU usage time. See for yourself:


The difference between the CPU usage with and without the PhysX processor was less than one tenth of a percent (The usages being 53.09% and 53.18%, respectively). Even with the tremendously powerful processors that we have nowadays, this CPU load would not even account for an increase by 1 frame per second. These results really left us with a sense of confusion. It does not make sense that there would not be a higher physics load on the CPU without the PhysX card. The only possible explanation for this is that the Physics effects in GRAW are relatively insignificant, or that they are “pre-loaded” so to speak in the constant processor load, meaning that there will be no spike in CPU usage when a physics-intense event occurs. If this is the case, the GRAW might simply not be a very good indication at all of the abilities of the ASUS PhysX P1 physics card.

As stated before, however, there really is no excellent way to test the abilities of these add-in physics cards due to the lack of sufficient software support. The largest scale of physics use that we know about can be found in a game called CellFactor. In this game you are an elite soldier-type guy who has weird psy-op abilities and a futuristic machinegun/grenade launcher. It is a fun game insofar as you get to make stuff blow up on a scale never before seen in any game. You can launch a grenade into a mound of oil drilling equipment stuff, and watch it be blown to smithereens. We would LOVE to see the difference in performance that the PhysX card affords in this game, simply because it is so intensely based on physics. However, without program code modifications, there is no way to play this game without the PhysX card installed. Therefore we are not in a much better position than when we started.