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AMD APUs cannot do 4 dual-rank DIMMs @ 2133MHz?

Question asked by rkvd on Nov 18, 2016
Latest reply on Nov 26, 2016 by rkvd

First, some background.


I already had a 2x8GB, DDR3-2133 memory kit (G.Skill F3-2133C11D-16GXL) working fine at 2133MHz. For whatever reason I wanted more RAM and found another cheap 2x8GB G.Skill kit (F3-2133C10D-16GXM). I saw the difference in voltage (1.6 vs 1.5) and timings and thought, well, it will be fine as long as I make all of them work at the same specs.


Well, they do work, but they aren't stable at all, and no fiddling with timings help. If I downclock them to 1866MHz, they work flawlessly. Even if I set everything to "Auto" in Setup, they are still fine with it.


In my tests I mixed modules from the two kits (one stick of each) and could run them at 2133MHz with no trouble. It's only when I put all four sticks on the motherboard at 2133MHz that they crap out.


CPU-Z says that they're all dual-rank DIMMs. I found this


DDR3 memory frequency guide


in the AMD website but it wasn't updated for Kaveri. I couldn't find anything on Google about it either. My motherboard is an MSI A88XM-E45, running an A10-7800 APU.


So, anyone else here faced the same issue? Would things be different if the sticks were all single-rank? Is that MSI's fault?


(By the way, I didn't see any significant performance drop, maybe because I could get the timings much lower than with 2133MHz.)