Hi, I bought a refurbished Mac Pro (8 core) from the apple store and added 4 Gb (2x2Gb) to the 2 Gb tht came installed. I am having a peculiar problem in seeing all four of the memory modules. The only setup that shows all 6 Gb of the memory is to have the modules in the following format: a) 2Gb modules on Riser A, positions 1 and 3 plus 1 Gb mods on Riser B positions 1 and 3; b) 2 Gb and 1 Gb mods on Riser A positions 1 and 3, respectively, and the same on Riser B. When I put them in the logically (and aesthetically better) intuitive configuration of paired mods in positions 1 and 2 of each Riser, I can only see the modules that are in position 1 of each riser. Is this something expected in the new MacPros? Is there a disadvantage of keeping this configuration? I note that a memory installation video on line stated that the way memory is installed in the early 2008 Mac Pros has changed. Does this issue result from that change?