I got 2 GB ram when I bought the Mac Pro. I added 4 sticks of 2 GB to get 10 GB. I now suddenly found out that I had only 4 left in the second Riser. I opened the Mac and moved the 2 1 GB sticks from Apple to place 3 and 4 of Riser A. I moved the 2 2 GB sticks from 3 and 4 to 1 and 2 and now I've 8 GB ram. The 2 1 GB sticks from Apple show empty in the System Profiler. I'll remove them later. The Mac is out of warranty. Paul Moortgat