For some reason it will not let me edit my posting above I just went back and found this document that makes it look like there may be two series of motherboards in the z400. One with only four memory slots and one with 6 memory slots. If this is truly the case then you can use three four GB memory modules BUT of course you will not be getting triple channel bandwidth. And I suspect that you would be better off using 4,4,2,2 configuration rather than 4,4,4,0. Besides it would be cheaper for only buying 2 each 4 GB modules
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