Can someone tell me; when I’m using two or three cards in SLI mode, will CUDA make use of the two or three GPU’s simultaneously.
I’m planning to buy a new PC with two or three cards to have more power for Premiere Pro in combination with CUDA to create H.264 1080p full HD movies.
I don’t know where els to place this question.


CUDA and SLI are mutually exclusive. The SLI link doesn’t function with CUDA at all (not that it would be all that useful in any case because it is not an especially high bandwidth bus).

But will CUDA use the multiple GPU’s for e.g. redering in Premiere?

That is completely a question for the developers of Premiere. CUDA doesn’t automagically use more than one GPU, if that is what you are asking. For an application to run on multiple cards simultaneously, the developers must implement some form of multi-GPU scheme themselves, CUDA cannot do it for them.

SLI is a technology for use multi-GPU for Rendering. You can use multi-GPU configuration on Cuda, since the 2.3 version, a SLI block is no see as one device. Now a day, you cannot direcly copy data beetween gpu without use CPU buffer (a mapped portable allocation is the well designed). An other possibility of multi-gpu programmation is to use OpenCL but is hight level and conssequently less optimal than Cuda.