If I'm not mistaken, the PC3 is based off the speed of the ram since the motherboard is either 100 or 200 mhz. You take it double it twice. The PC3 should be on the actual RAM stick itself. However, I would recommend getting a combo set. In theory, getting the same exact RAM should work, but you can run into problems. I'm giving you both options, because if one fails, you can try the other.