Originally Posted by
GarageYears
I cannot say definitively, but the latest simulators generally use the SAME software load, delivered as a binary, as the aircraft.
I think it's generally safe to assume that a full-flight Level D simulator uses at least a direct derivation from the FMC load. There are quite a few different 737 simulator models out there, built by numerous companies, and you would need to know the specifics of the simulator in question.
Some simulator manufacturers design "hardware in the loop" simulators running the actual flight-qualified aircraft FMC hardware (and hence the actual software binaries, loaded using aircraft-representative methdos). Some start with the binary software load, and run it through a software conversion to make it compatible with the simulator host computer. Some create simulations from scratch based upon the known operation of the aircraft, although that's uncommon on commercial full-flight simulators; it's much more common in the military simulation world.
Using flight-qualified software and hardware in a simulator can present some challenges, by the way. Aircraft FMC and navigation software generally doesn't like simulator freezes, resets, and repositions, which are common in training. If the FMC software doesn't provide "hooks" for telling it to play nice in a simulator, it can be necessary to simulate the software instead of implementing it directly. I've seen some pretty odd simulator behavior because the FMC didn't understand why it was suddenly 28,000 feet higher and 400 miles away from its last known position.