I recently grabbed a Power Mac G5, and I got it with 4.5GB of RAM: two 1GB modules, two 256MB modules and four 512MB modules. I'm trying to upgrade it just for fun. I can swap three modules: replace the 256MB modules with 512MB modules and one 512MB module with one 1GB module. With this configuration, it'd be three 1GB modules and five 512MB modules. It's my understanding that the modules need to be installed in pairs, but so far, every configuration of memory modules I tried has yielded no success. First, it dropped to 3GB of RAM, then 1GB and every one in between. I'm swapping the modules between slots to figure out which is correct. I've also found a diagram online that displays the identifiers for the RAM slots, so I'm trying to match them up. Can someone help me out? Can I even do three 1GB modules?