It works the same as the ATI technology with up to 2.8x the performance of a single graphic cards solution.
In order for SLI To run, your PC needs to be equipped with an SLI-Certified Motherboard and 2 or 3 SLI-Certified GeForce GPUs. It is also recommended that you used an SLI-Certified power supply and chassis for its maximum stability.
SLI Performance chart:
As you can see, the chart shows the performance of the SLI almost 3x the performance of a single graphic card solution.

