I have a question about ram size modules: is possible to have something like (4GB + 8GB) + (4GB +8GB) ? or even (4GB + 4GB) + (4GB + 8GB) ? I have not tested :-( now I have a factory : 4 + 4 + 4 And I want to ask if: the bios is refusing the configuration ? or is only a performance issue? I have found out this: MacPro firmware prefers not mixing 8GB with other modules http://macramdirect.com/macpro.html thanks f.c.