10 Replies Latest reply on Nov 27, 2016 8:20 AM by rkvd

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


      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.)

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

          This is the last line in the spec's for the memory you selected.

          "Combination with other memory kits or modules (even with same model number) is not recommended to avoid any compatibility issues"

          G.SKILL Ripjaws X Series 16GB (2 x 8GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3 17000) Desktop Memory Model F3-2133C11D-16GXL …


          It has always been the rule not to mix and match memory.  If you want 32GB of RAM, you need to purchase it as one set of 32GB.

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

              I know that. These kits are very expensive where I live, I don't want to burn money in one of them just to find out that I can't get it to work at the rated speeds.


              Maybe my original post was too long-winded, so here's a summary (the old kit is red, and the new kit is blue):


              Two sticks of the blue RAM @ 2133MHz = OK

              Two sticks of the red RAM @ 2133MHz = OK

              One blue stick and one red stick @ 2133MHz = OK

              All four sticks @ 1866MHz = OK

              Four sticks @ 2133MHz = trouble


              I test it with memtest. At 2133MHz, the memory passes all tests but the 7th one (block move).

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

                  AMD processor cannot handle 4 sticks at top speed so use 1866 and tweak the timings to perk up the performance

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

                      That's what I did and it worked great. However, I have been looking into other boards' specs and they claim to have run 4x8GB at 2133MHz. Of course I don't take their word for it (they could have just powered on the system without checking the stability to inflate their specs). The evidence I have does point to a motherboard issue, but I'd have to rule out the processor and I... don't want to bother with that anymore. I'll mark this as answered.

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

                          AMD does NOT claim that their CPUs/APUs will support 4 DIMMs above 1866 MHz. While some mobos/CPUs/APUs will run 4 DIMMs at 2133 MHz or higher frequency, this is always when using a matched set of DRAM rated for the higher frequency. Mixing DRAM automatically limits the ability of the DRAM to run at higher frequencies reliably because the DIMMs are rated as an individual DIMM or one DIMM kit. When you combine two DIMM kits with identical frequency ratings they are not likely to ever run at the stated frequency or timings as four DIMMS because you did not buy a matched set of four DIMMs in ONE DRAM KIT that were tested and confirmed to run reliably at the higher frequency. As such even with slower timings it's unlikely you will ever be able to run all four DIMMS at 2133 MHz. There might be rare exceptions but they would be few.


                          Now as a public service you will find with your own testing or accurate independent testing that DDR3 DRAM running at 1600 MHz. is NOT a system bottleneck on a single CPU desktop computer. A single APU powered desktop can use up to 2133 MHz. DRAM to help the GPU section of the APU process data faster. Any RAM above1833 MHz. for a single CPU and 2133 MHz. for a single APU powered desktop be it AMD or Intel, is a waste of money as the higher frequency DRAM provides NO tangible system performance increase. In addition DRAM timings on DDR3 DRAM provides even less system performance gains than faster DRAM which is effectively nothing so don't pay more for faster timing or higher frequency DRAM as you will see NO tangible system performance increase. If in doubt conduct your own test with your DRAM set at 1833 MHz. and a higher frequency running REAL applications, not using bogus benches. Beware that RAM benches assume the DRAM is saturated 100% of the time and thus show DRAM potential not actual real world system performance gains by using higher frequency DRAM than appropriate.

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

                              Actually Intel systems see a good fps advantage from using higher speed memory in gaming (that counts as real world right?)


                              AMD FX CPUs peak around 2133-1866Mhz (Mobo dependant), AMD APUs greatly benefit from high speed mem if you're using the iGPU.

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

                                  In the MSI command centre  there's an option to bump the DRAMM voltage. Worth a try, just don't get carried away.

                                  My MSI 88X board defaults to 1.5000 and 1.5100 is the next step.

                                  IIRC, my old gigabyte board needed .05v - .075v more to get 4 dimms error free at the desired speed.

                                  Also you might find some MSI insight  on their own forum... maybe..

                                  OTOH what techguy says regarding ram speed and real world effect is good advice.


                                  Good luck and be careful.

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

                                      As much as I like this board, it leaves a lot to be desired in regards to fine-tuning/overclocking. There's no small steps for anything (DIMM voltage is 1.35, 1.5, 1.65 and 1.8; there isn't much choice for memory speed as well (just the standard 800-1333-1600 etc.). No tinkering with timings or voltage helped anything: the errors are always random and non-repeatable, which suggests that whatever is holding the memory back (the mixed kits or something else) is out of my reach and control.

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

                                    I'd have to sell the two kits I have, the computer and one of my kidneys (and maybe a chunk of my liver) to buy a 4-DIMM kit, so I won't dispute whatever you're saying.


                                    (Tightening the timings did seem to help, though.)

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

                                  They can handle them if you are prepared to tweak them, 4 x 2133 sticks are fairly straightforward, 4 x 2400 on the otherhand is a little trickier.