Try placing the largest memory module into Slot 1. 8GB in slot 1 and 4GB in slots 2,3, & 4. The worst thing that can happen is the Mac Pro won't boot. If it does start up, then OS X will notify you if the memory is installed in the correct confiuration.why was i told by owc that i cant they toled me that it has to be 4 gb all of them. Will i get any problems if i place another 8 gb with 3 sticks 4 gb i will have 20gb if i do this
In the early days of the 4,1 8GB DIMMs could not (and they were not available even to use or test in early 2009) - but that changed in the year afterwards, maybe by the time the Mid-2010 came out.You can't do that, no. 8Gb DIMMs can't be mixed with smaller modules, the Mac Pro won't pass POST if you try.