It is not clear in the manual.
In sample configurations, with 2 processors.
For 48 gb it says use 6 x 8gb.
But I have got
8 x Crucial 4GB DDR3L-1600 ECC UDIMM
4 x 4GB DDR3 - Synchronous Unregistered (Unbuffered) (came in system)
There are 12 slots and it says on Crucial, Max Unbuffered DDR3 SDRAM:48GB
if not what can I put where to get maximum ram?