Well, our Mac Mini server 2010 has a mere 4GB of memory and we wanted more of course. However PC8500 ram is very expensive, so we got the much cheaper ($180 for 2x8GB PC8500 vs $120 for 2x8GB PC12800). But the problem is putting in both doesn’t work.
It appears that the Mac Mini needs one stick of PC8500 ram in the bottom socket otherwise it won’t boot properly. Maybe because the chipset can deal with PC12800 but not the Mac Mini.
Testing (at Macrumors Forum) shows that it can also run 1333 MHz (DDR-12800) if there is only one stick of RAM in the bottom socket, so it looks like the easy maximum is 10GB for right now until we find some more spare DDR-8500 memory around. But it works now at 10GB 🙂
Most interesting is that with a single stick, it will actually boot in 1333MHz mode, so you can either
Slot 1(bottom) Slot 2(top) Boots Speed 1G 1G Yes 1067MHz Standard Installation 1G empty Yes 1067MHz Testing configurations empty 1G Yes 1067MHz Testing configurations 4G empty Yes 1333MHz 4G 1G Yes 1067MHz 1G 4G Yes 1067MHz empty 4G No Single Beeps 4G 4G No Single Beeps