I was recently asked to upgrade the RAM in a G5 tower from 4 GB to 8 GB. My understanding is that while the G5s with PCI only allow upgrades to 4 GB, the PCI-x models (which were the top-of-the-range at each release) allowed up to 8 GB to be installed. This is one of the PCI-x models, so I bought 8 compatible 1 GB chips and chucked them in, expecting the machine to happily see them. But, it only recognised 4 GB. Funny thing is, I then had a look at the old chips I took out - there was already 8 x 1 gig chips in it, and it was only recognising 4 GB of them as well! Anyone have any ideas why I'm only having 4 gigs recognised? Is that all this machine can take? Is it just recognising one of the 2 groups of RAM slots? Has anyone else had this issue?