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Sli?

post #1 of 5
Thread Starter 
I read about this but just want some more clarification...
1)when you have 2 cards running does one have to be dedicated physics?
2)why cant you just let the cpu be dedicated physics and have the cards be processing all the other things? or is it redundant and doesn't work that way?
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post #2 of 5
1) With two identical cards, you'd be doing SLI. With non-matching cards, you have the option of dedicating PhysX to the weaker card. SLI is (in the vast majority of cases) the more practical option, and will get you better performance.
2) The GPUs are able to handle PhysX much, much better than the CPU can. This is just one small example, from here:


So it's better to let the GPU handle PhysX.
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post #3 of 5
1) No. Regardless of the number of cards installed in your system, you can still choose to process Physx with your CPU. Or, you can turn off Physx from within the game.
Take a look at your Nvidia Control Panel, you should have the option to choose either your GTX570 or your CPU to process the Physx.

2) Yes. You can go into Nvidia Control Panel and select CPU to process the Physx. Most of the time, this is not a good idea because the Physx effects are usually too heavy for a CPU to process, thus resulting in much lower framerate. Take a look at the chart below. Using a Phenom II X6 to process the Physx effects of Mafia II, the fps is only 14.8.

A side note:-
For certain games (eg Mafia II), if you have a higher end SLI system (eg GTX570 SLI), the framerate will be higher with the SLI disabled (ie with master card doing graphics rendering and the slave card doing Physx) than with the SLI enabled (ie with both cards sharing graphics rendering and with one card taking up Physx as well).

Edited by windfire - 10/24/11 at 6:53pm
post #4 of 5
Thread Starter 
so if i have 2 gtx 480s then i should dedicate one to physics and not let my cpu do the work?
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post #5 of 5
Quote:
Originally Posted by smokebaca View Post
so if i have 2 gtx 480s then i should dedicate one to physics and not let my cpu do the work?
Yes. Physx effects are always done better by a graphics card than by a CPU, at least up to now with my knowledge.

I would just choose 'Auto' and let the drive decides. Usually it will choose the slave card of the SLI pair.

As I mentioned above, for some games, it might be better to disable SLI and then select the slave (ie second) card to do Physx while letting the master (main) card to do the graphics rendering.
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