FPGA+RT Architecture and Design Decisions

Hi guys.

I have a question specifically relating to the sbRIO-9651 that I am working on, but would also be interested in more general answers if all RT and FPGA devices work the same.

My first question relates to the architecture of the hardware. Is the RT and FPGA in parallel or in series? So does the signal go Windows PC -> RT -> FPGA or would it go PC->RT and PC ->FPGA?

My second question is, what is the purpose of having both RT and FPGA, and how do you decide which one you wish to use? If you wish to use both, why is that?