the 790i ultra chipset supports 8gb of mermory max. And there were no 4GB dimms made when that board was made...so there are no 4GB dimms that will work for that board. keep in mind that the newer dimms are made for the i7's and i5's (1156 socket) are not fully compatable for the older 775 socket motherboards. you need the 1.8-2.0v ram that is getting harder and harder to find. Not only that, but just to run 8GB of ram (all slots populated) the speed and timing of the memory sucks. I have patriot DDR3-16000 2000MHz ram made for this board and it will run at 2000 MHz with just 2 slots occupied, but when I put in all 4 chips...I have to change the speed to 1067MHz! This is common with our boards.