I upgraded the CPU in my 4 year old PC (Dell Inspirion 660) that had an Intel Pentium Dual-Core SR10H with a quad core i5-2500S. PC works better, though it no longer likes a ram memory card in the second slot (doesn't get past the POST, beeps twice, meaning ram issue)(had a pair of 4GB cards before). The machine is Win 7 64 bit, so the 32 bit limit of 5GB shouldn't be a factor. Can't find any reason for this yet... Tried putting the old CPU back, machine still doesn't like the 2nd memory card (I did try both cards, one at a time in the 1st slot, both work). PC works better with the quad core despite less ram, though I'd like to be able to have the 8GB I used to have.