I just purchased a Mac Pro. Its fabulous, does everything crazy fast, but will not recognize all of the RAM. I have run the hardware tests, and everything passed. For further background info, the Mac Pro came with a standard 2 GB (2X1GB) and I bought 8 GB (4X2GB) from OWC for a total of 10 GB. To simplify things, when I refer to slot 1, I mean the combined total of slot 1 in both RAM cards. Here are some tests I've done. Configured this way: Slot 1: 2GB Slot 2: 4GB Slot 3: 4GB Slot 4: 0GB It recognizes 6 GB Configured this way: Slot 1: 4GB Slot 2: 2GB Slot 3: 4GB Slot 4: 0GB It recognizes 8 GB Configured this way: Slot 1: 2GB Slot 2: 0GB Slot 3: 4GB Slot 4: 4GB It recognizes 6 GB I have come to the conclusion that the slots 2 and 4 are broken. Is there any other possibility?