Just to expend slightly on that, it's the FMC position which is being refined from all of the inputs described above. It likes GPS best, then DME/DME and so forth. It's constantly comparing and refining the pos. It navigates, then using the derived pos. The pilot interfaces with the FMC through his CDU and tells the system where it's to go, but the heavy lifting is all gone now. Even on non prec. approaches now you use the FMC to fly the approach and do a cursory monitor of raw data as a gross error check.