I don't know if you are asking to compare systems or you are looking to upgrade the amount of RAM you have but remember you can only use RAM that your motherboard supports. If your Mobo supports DDR then you use DDR, same with RAMBUS. If your motherboard uses 16 bit RAMBUS (the ones where you have to have two sticks at a time) it won't support 32 bit RAMBUS (it is physically different.)