Well, it's like this. I have a PowerBook G4 with 1 GB in RAM. I checked the memory in about this mac and got this: So, I purchased an extra stick (1 GB) and when I was about to install the new stick I found that the lower slot wasn't empty, it had another stick of RAM in it. These two sat together making 1 GB of RAM, but showing it as only one in the about-section. How come? I also tried to make use of my newly bought RAM and thought "1,5 GB is better than 1 GB..." but the lower slot still claim it's empty and therefore the "about this mac" tells me I'm down to just 512 MB of RAM. I'm very confused!