I am thinking of upgrading memory in my Mac Pro 4,1 single processor and I am wondering if anyone has tried or knows of any negative effects of using rank 4 Memory? I have spent a few hours on the Web and all I could find was that most Max Pro approved memory modules are dual rank (rank 2). I also read on a couple sites that higher rank memory chips can reduce your max ram capacity. I don't quite understand the meaning of rank nor if it effects a Mac Pro. Any help will be appreciated.