When I purchased this motherboard, I purchased 2 GB DIMMs. I have need to increase to 4 Gb but when I put a DIMM into either of the DIMM 1 sockets, the computer will not boot. I thought it might be compatibility, so I just ordered (4) 1 GB DIMMs from G.Skill. Again, with DIMMs in the DIMM 0 sockets, they work and I have 2 Gb, but if I add any to the DIMM 1 sockets it will not boot. I've placed each of the 4 DIMMs into the 0 socket and they all work. I checked for current BIOS and I have the most recent for this board.