Sigmet is correct. You will get very in depth discussions about the technical aspects of the 747-400 on the aerowinx (if it's still like it was a few years ago when I monitored it for a bit).
Precision Simulator is by all accounts a very accurate and complete simulator. The outside world is very skimpy but the controls and systems of the 747 are far superior to what you can get from other software which usually based on MS FS and is constrained by it. The complex interactions between all the systems are all there and you can program endless emergency situations. The FMC is similarly more-or-less the same as the real thing - even varying between airlines and engine types.
If you are at all interested in the 747-400 I would recommend you consider purchasing this product.