SimGuruGraham has just confirmed that The Sims 4 will utilize a 32-bit executable. This means that if you have a 64 bit operating system, the game will only access 4GB of memory (RAM), even if you have more.
I asked about this recently. We won’t have a 64 bit exe; it’s fairly uncommon for games. Our lead ENG explained to me why Sims 4 wouldn’t particularly benefit from it and it sounded quite reasonable, but I’m not comfortable enough discussing tech to try and repeat his explanation.