I have a GTX470 and use the Cuda Cores to aid in video compression. If my mb supports SLI, will buying an additional GTX470 effectively double my CUDA cores to be used by my video compression program? I believe the GTX470 has 448 CUDA cores.
The simplest answer is no. If the software you are using hasn’t been specifically written to use multiple GPUs, then adding a second card won’t change anything. SLI has nothing to do with CUDA.
I am waiting for someone to program a transparent CUDA wrapper that simply splits the grid and distributes it across several devices. This might work for some kind of applications (the embarrassingly parallel type).