I still use XP Home 32 bit, so I am limited in the amount of RAM that I can use. I had been using 2GB (2 x 1GB DDR-800) and that was "ok", but I felt I could do better. RAM is cheap these days, so I purchased new memory, 2 x 2 GB DDR-800, so I would have 4 GB. My operating system reports seeing 3.5 GB and this is normal for a 32 bit OS. Moving from 2 GB up to 4 GB did not improve my frame rates, but it seems to have greatly reduced stutters. In short, I think if you are running a 32 bit operating system, then go ahead and install 4 GB of RAM, preferably two 2 GB sticks as that configuration uses less energy, generates less heat and usually runs slightly faster than four 1 GB sticks. If you have a 64 bit operating system, then you should not have anything less than 4 GB of RAM.