Flight Simulator 2004 and Flight Simulator X were programmed to run on 32-bit operating systems and until now there was no problem, but with the increased quality of the addons and if we maintain the Flight Simulator with a high level of graphic requirement, each time more often we will have a CTD (Crash To Desktop) because of the famous OOM (Out Of Memory). This is because although we are running a 64-bit operating system, Flight Simulator 2004 and Flight Simulator X works under 32-bit, so although we have 8 GB of RAM, if you use the 2.5 to 3 Gb. which is recognized by the 32-bit operating systems we will have an OOM.
Fortunately, users of 64-bit operating systems are in luck, as Daniel Pistelli has created a little free utility that makes the Flight Simulator working in 64 bits. The operation could not be easier, simply run the utility, select the executable file (fs9.exe or fsx.exe) and problem solved, bye to annoying OOM.
Although I personally have not noticed differences, some people have reported significant improvements in the performance of the Flight Simulator once patched. I had no news of any problem generated by the patch either, so I think it is advisable to use it.
In theory and although it is a 32-bit software, Prepar3D does not need this patch due to a better memory management
You can download the utility here