These games are programmed with 32-bit instruction sets. Even you have memory more than 4 Gb and a 64bit OS, they will just took up at most 4Gb when they are running. There is not much 64-bit programes or games in the market, WinRAR have 64bit version and you can see some difference. The actual need of these memory is low, but when there are more 64 bit instruction applications roll out, there might be some difference. 64bit PC Architechture and OS have been avaliable for quite some years and basically most hardware are not 64 bit ready, but the infiltration rate of 64 bit programs never match up. Probably 90% of the games/applications are still 32 bit x86 instruction set. Check hard drive, how many are under Program Files (x86) and how many are under Program Files folder in a 64bit MS OS.