I am working on two different X51 builds from parts. I see the R1 has the 1155 socket as the R2 has the 1150 socket. One motherboard was bought after I got the first case, the second one was a used board I got. I got the parts several months back and was thinking the socket on the motherboards were 1155. I purchased a Pentium G2020 2.9 dual core for cheap to test the boards out. This goes into a 1155 socket. I can't get either board to post. Googling the numbers on the motherboards doesn't bring up a single hit, but when shortened I get way too many links with conflicting info. Is there any sure fire way to tell the difference between the R1 and R2 motherboards so I make sure I have the correct CPU before doing further testing.