My recommendation if unsure of the number of GPUs in a windows system is to check Device Manager. Alternatively, if you have physical access to the system, look at the I/O area of the case and count the cards, or open the box and count the cards.
Also note that in device manager, GPUs like Tesla K10 and GeForce GTX 690 (and there are some others) will show up as 2 GPU adapters, even though there is only one physical card. However, for logical and programming purposes, these devices will show up as 2 separate adapters. Likewise, CUDA will enumerate them as 2 separate GPUs, so that you can for example use cudaSetDevice()
to select one or the other. Cards like these are effectively two GPUs in one.