I'm thinking your wanting the difference between 64bit and 32bit operating systems. Well imagine this, a 32 bit arcetecure is like a 4 lane highway, you can move a lot of cars in either direction with little slow down. However, a 64 bit arcetecutre is like an 8 lane highway, now you can move twice as much traffic in both directions. So 64 bit = better. Now that being said, at this time there isn't a whole ton of programs that can fully use this technology, but as time goes on it will. So in short, go with the 64 bit as long as you have a 64 bit processor, otherwise your processor is going to waste.