SLI Question

I have a pc with the following specs - i7-4790K and 2x GTX780Ti SLI

I've noticed in the SLI configuration under PhysX settings > Processor you can set card 1 or 2 and Dedicate to PhysX. This gives varied performance depending on the game. I have to play around with this by way of trial and error to get smooth 60FPS VSYNC. I don't understand why some games run better with Card 1 and some with card 2 and what does dedicating a card to PhysX do? Sorry for the noob questions, I am new to the "PC Master race".

Ignore those options and leave it as automatic or GPU 2 if need be.

GPU accelerated PhysX is a physics API that is rarely used.

• When you are given the option to select a card to do PhysX processing, you are just telling the driver which one is going to do the PhysX processing while SLI remains in tact. (in a game that uses GPU accelerated PhysX).
• When you are dedicating a card to PhysX, you are disabling SLI in that config and telling the driver to ONLY use that card for PhysX processing. This is best used when you have a weaker Nvidia card or a spare card and just want it do to PhysX.

Just don't choose "Dedicate to PhysX".

k...

Hey thanks a lot, this clears up a lot. Is this why some people use 3 way SLI? 2 cards for SLI and the third dedicated to PhysX? I don't mind spending a lot of money to get the optimal performance but it seems a bit excessive to get another 780Ti just to dedicate to PhysX when it is rarely used.

Yup, this is only done when you buy some low end GTX GPU for PhysX use alone.

No, don't do that, people that use 3-4 way SLI is either for benchmarking or 4k display (any resolution above 1440p)

People run 3 - 4 Way SLI to be able to run a 4K resolution or X3 1080P monitors. These kind of setups require lots of GPU power.
Your system with X2 GTX 780 Ti's is way more then enough power even for 1440P.
It'd be a waste of money to get a third GTX 780 Ti. Spend that on something else like a 1440P monitor if you don't have one.

No. When you see someone having two 780TI in SLI and a weaker card like a 750Ti in one system, it usually means that they are using the 750 Ti for PhysX and the two 780Tis for game processing.

You can use any cheapo Nvidia card for PhysX as long as it has enough CUDA cores. It doesn't have to match your primary cards, but now a days it's silly to have since so few games actually use PhysX.