Overclocking RAM for an APU

Hello everyone!
Today I wanted to ask a question about how to overclock my RAM.

I currently have 1 stick of 4gb Gskill DDR 1600 (F3-12800CL9S-4GBRL), and about to buy my second stick in 1-2 weeks.
I also have an APU A10-6800K, with it's graphics module (HD 8670D) overclocked to 950 MHz.
My motherboard is a basic one, MSI FM2-A75MA-P33, so voltages may not be completely accurate (and I can't even set the CPU voltage)

So far I've been able to find 2 stable overclocks for my ram, and those are:
1866 9-10-9-28 at 1.5v
2133 10-11-10-30 at 1.65v

(I still have to try to lower timings a bit more, any recommendations?)

As you may know, APU's performance is really dependent on RAM speed and timings, and I would like to know which setting is the most beneficial for my current hardware. Should I stick with 1866 with low timings, or is the 2133 setting better?
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  1. Best answer
    GPU/IGPs have mostly linear RAM access patterns which makes them almost entirely dependent on RAM bandwidth. That's how GPUs can afford to use GDDR5 RAM with timings like 22-22-22 or even worse yet still deliver high performance.

    CPUs have highly non-linear access patterns and that's why things like VisualStudio Firefox or GCC Linux Kernel build benchmarks (or just about anything else related to compilers, interpreters, emulators, etc.) are much more heavily dependent on low latency.
  2. InvalidError gives some great details on some very important concepts in a very accurate fashion. However, you may also find this useful: According to the ROG forums there's this formula to help: (CAS Latency/Speed)*2000 gives you a value in nanoseconds to compare memory (lower is better, so for your two setups it would be:
    (9/1866)*2000= 9.6463 nanoseconds vs
    (10/2133)*2000= 9.376465 nanoseconds
    giving the 2133 setup a slight edge. Hope this helps!


    Justin S.
  3. So, you're trying to say that the integrated GPU from my APU will get better results working with 2133 CAS 10, rather than 1866 CAS 9?
    If that's so, I will choose the faster transfer rate.
    I know the difference I will see is minimal, so I also wanted to know a bit about voltage and reliability. With a cheap motherboard like mine, is it safe to use the 1.65v setting?
    I know the big change in performance will come when I get my second RAM stick, so I'll be able to use dual-channel, but in the meantime I'm trying to squeeze every bit of performance I can get (and at the same time practice my overclocking).

    So, I should choose the higher value (2133), right?

    By the way, thank you very much for that information, it's great to learn something that specific, I had no idea about GPU and CPU access patterns.

    Oh, and according to the second reply, the 2133 CAS10 has even better timings than the 1866 CAS9, so I guess there's no doubt left, Ill just choose that one.

    Thank you both very much!
  4. According to newegg (no I don't work for them) your board is listed to support 2133 ram:
    So as long as your temperatures are within the normal range I wouldn't worry about it. If you want longevity obviously you can choose to give up some of the performance gain to ensure cooler running temps (if that's what you observe). It's up to you to determine if this gain in performance outweighs the temperature gains. Based on your statement that you want to "squeeze every bit of performance you can get..." then you should stick with the 2133 setup if your system can remain stable and at reasonable temps.
  5. So far I haven't seen any temperature issues, and I don't plan on using this system for longer than 1 year (if I'm lucky with my job), so I believe I will stick with the 2133 setting. Thank you very much, not only for your help, but because you both also taught me something very useful which I'll be able to use next time I encounter a similar question.

    At first I regretted buying 1600 ram instead of 1866, but it ended up being a great deal with these new settings :D
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