After reading about RAM configurations and how to install them, I purchased 4x1GB modules from OWC and kept the stock 2x512MB RAM. Here's how I arranged them: Riser A: 2x1GB at the front, 2x512MB at the back Riser B: 2x1GB at the front, none at the back For a total of 5GB. After booting up, the Mac only recognized 4GB. I thought something might be dead, so I took out the 2x512MB modules and booted again, and it told me 4GB, which is correct. My question is, was my system supposed to recognize the 2x512MB modules, or are they not supposed to be there in the first place?