Yes, they are both ECC, I double checked just to make sure. I tried putting them in and they wouldn't fit so i went and looked them up. Then powered down thinking maybe i made a stupid mistake putting them in backwards, but they still don't fit. The only difference I can find in the RAM is the ones I ordered are buffered and the ones installed right now are not. I'm not worried about the new ones working with my original ones, im just looking to replace the old ones. Maybe the buffered RAM is slightly different? I have never dealt with buffered memory. Anyone? Thanks in advance.