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Questions for a 3900x build

Hi guys,

I am going to be building a Ryzen 3900 based PC but since it has been a few years since I have actually built a PC of my own I was just hoping you guys could clarify some technical questions so I buy the right parts.

  1. I am aware that with Ryzen 3000 the IF runs 1:1 with ram up to 3600 (or is it 3733 I kept seeing this speed being referenced when Ryzen 3000 was first announced) and after that the bus works at a different ratio. If my understanding is correct one could manually set IF clock so if I had memory say clocked at 3800 I could set the IF clock to 3800 (as long as the CPU can manage it) to maintain 1:1 clock ratio to avoid any latency hits. Is my overall understanding of this correct?

  2. In the past running more than two DIMMS would mean you couldn’t run the memory at higher speeds. Is that still the case with Ryzen 3000? I am a software developer so I could use 32 GB’s of ram so I am wondering if I could get a 4 dimm kit and run at the rated speed. For example there are 4 dimm kits that are rated at 3600 mhz of Trident Z Neo which from what I understand are designed for Ryzen 3000. Does that mean if I picked up one of these kits the ram will run at the rated speed in my system? If it maters I am looking at getting the Gigabyte Aorus Master mother board.

  3. Previous Ryzen CPU’s had issues running past 3200 from my understanding, if I was to use a x470 based motherboard with the 3900x should I be able to run at 3600 MHz ram? Or are the memory traces also better to support higher speed ram on newer motherboards.

  4. Lastly how likely is it possible to run memory past 3600 MHz on the 3900x? From what I am seeing running the memory at 3800 MHz should be very possible.

Thanks in advanced.

The speed that the infinity fabric decouples from the 1:1 ratio is at 3800 or faster, so 3733 is the fastest you could clock the RAM up to before this occurs.

However it also appears that for many apps the ram speed from 3000 up to 3600 doesn’t seem to make a lot of difference.

Many would say that 3200 is probably the sweet spot for speed.

As for running 2 sticks vs. 4 sticks, these seems to be less of an issue with the 3000 series CPU’s as they seem to have a much better memory controller along with many improvements to the BIOS.

Also there are higher density RAM modules now, pretty sure you can get 32GB modules but pricing may not be very good due to the higher density RAM cells.

Thanks for the response!

That clarifies the 3733 figure I kept seeing. A question I have this once the speed is decoupled could I manually set the IF to keep the 1:1 ratio? Ie if I could OC the ram to 3800 (not sure how practical this is but I have seen posts saying certain 3200 kits can be oc’ed pretty high) could I bump the IF manually to 1900 to maintain the 1:1 ratio?

Thanks again!

edit: Mistakenly made it sound like I expected the IF to run at 3800, so modified my wording in the last question.

I don’t think so, this is due to how the infinity fabric works timing wise.

Seems to be a good rule of thumb to keep that speed at exactly half the RAM speed, so if you have 3600 speed RAM then the infinity fabric should be clocked at 1800.

I’ve also seen that many of the CPU’s may not be able to clock that high so the infinity fabric has to be clocked lower or you just clock the RAM speed lower to make it stable.

So maybe the CPU can clock the infinity fabric to say 1600 or 1700, then you could clock the RAM at 3200 or 3400 respectively.

Hi thanks again, oh ok I was under the impression that all CPU’s would be able to clock the IF bus to at least 1800. So I assume the only guaranteed clock would be 1600 since the official supported ram speed is 3200?

Thanks again

Correct, it appears however that the 3900x has the better memory controller, probably due to the AMD Binning process for the higher core count CPU’s.

Let me chime in and also advise to pick 2x16GB instead of 4x8GB. First of all it will run in dual channel (if you wamt quad channel, picl threadripper) and second, chances are that you’ll get dual rank RAM and Ryzen 3 seems to strongly profit from it.

Also, I’d recommend these two vids:

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I too am looking for Ryzen 3900x info thanks.
So much to consider in this generation like the ram MHz/timing

Anyone know much about the difference in memory brands they all come from Micro, Samsung, Hynix.

I’ve been looking at gskill kits is the
G.Skill Ripjaws V 32GB 2X16GB DDR4 3200MHz CL16
model: F4-3200C16D-32GVK
the same as the

G.Skill Ripjaws V 32GB 2X16GB DDR4 3200MHz CL16
model: F4-3200C16D-32GTZR
?

It is possible but its also possible that the system randomply crashes, has WHEA ERRORS or other “funny things”. If you are aware of that, you can try it.

That is a general technical limitation due to the high frequencys we are having on the boards.

But the real answer is: Depends on the Board, if they are designed for max. performance with one DImm per Channel (Daisy Chain) or the T-Thingy for optimal performance with 2 Sticks per Channel.
But DDR4-3600 might be pushing it, though with the right Boards, that might be possible.
The bad part is that it IIRC isn’t listed on the Spec part of the Motherboard. So you have to dive deep into that stuff.

That was more of a Board issue than a CPU Issue, mostly (cheap) 300 series had problems with that.
And also the Memory was also a part of that. Some older Sticks only worked on Intel. But in that case, if it still doesn’t do with a modern BIOS Update, you either have a shitty board that can’t do it (ie Biostar X370GT7 or so I’ve heard. Can’t say anything about it because it died before I got my DDR4-3200 Memory).
But with a good X470 Board, it should work without issues.

It is.
But the real question is:
Is it worth it. And here the answer looks to be: NO!
DDR3200-3466 with low latency seems to be a better idea than faster memory. Hardwareunboxed and others made Ryzen Memory Videos/Articles recently. ANd it shows an advantage of lower latency but slower memory.

Hi all,

Thank you for all the responses.

I am aware it will run in dual channel, I just wanted to be aware if I am locked into 2x16 or if I could go 4x8. In my admittedly short search for memory I think I noticed that higher density ram tended to be slower, I am probably wrong about that though. In my short search I was having problems finding ram.

Thank you for the info I was not aware of that.

Thanks I will have to look into and take this into consideration. Would it be better to get a 3200 low latency kit and then clock it to that range as that does seem to be a doable number to hit or would it be better to get something like a 3600 with a higher latency kit and then down clock it and adjust the timings to lower the latency.

Thanks

This is more or less correct, but is single rank vs dual rank. single rank tends to clock higher.

That said, it really doesnt matter man. The difference is so small now that you can clock infinity fabric separately from ram clocks. You’re really looking at speed differences that are next to unnoticeable. Technically higher clocks on ram are better for communication between cores because by default IF is running at half the data rate of RAM. This isnt a problem on zen 2 though.

cl14 3200 is technically faster than cl16 3600 but I wouldnt really concern myself with that.

Interesting, I would have thought the speed increase for the IF would be more beneficial. I guess intercore communication isn’t as much of a bit deal as it was for the first Ryzen.

Anyways thank you very much!

The speed increase is more beneficial if the CPU is actually moving information core to core.

cl14 3200 is a smidge better but as was discussed, you can just increase IF clocks to say 1900 and reap the benefits of both.

  • Asus does state that they use Daisy chain memory topology on all their X570 boards.

  • Asrock x570 boards are all T-toplogy.

  • Gigabyte not fully sure about all their boards.
    But i suppose they use Daisy chain as well.

  • Msi not sure, but likely also daisy chain.
    Still need to re-search this.

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According to choosing a board for a 3900X,
i would personally just go with a decent X570 board really.
I mean why would you limit your nice highend cpu,
with a previous gen mobo, that does not have pci-e 4.0 support.
Also you are looking to get the best stability from a memory OC,
so then i would certainly go for a decent X570 board.

If you want to run 4 dimms, then Asrock X570 Taichi,
is a very great bang for buck board.

If you want to run 2x16GB dimms, then you likely going to,
be better off with a different mobo brand,
if you want to get the best OC out of your memory.
But of course this also depends on the said memory modules,
and of course a bit of luck.
Nothing is really guaranteed when it comes to OC.

  • Asus crosshair 8 Hero.
  • Gigabyte X570 Aorus Master.
  • Msi X570 MEG ACE.
  • Asus X570-E Strix.
  • Asus Pro WS X570 ACE.
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Why is the Taichi recommended for running 4 dimms? In my case I am only planning on using a x470 temporarily as I have one in hand and then moving over to a Aorus x570 Master. According to buildzoid the QVL for this motherboard has a lot of 4 dimm kits listed as supported. That said he didn’t actually test the board. Does anyone have experience with this board?

Thanks

Well Asrock is using T-topology on their X570 boards,
which ¨theoretically¨ should work better with 4 dimm configurations.
Most other brands use Daisy chain memory topology,
which should be better with overclocking 2 dimms.
But of course this is all theory, in the real world there are more factors in play,
like for example which particular memory kit you have, board compatibility,
and how much luck you got with your particular cpu.

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Indeed, many things can play into a kit using 2 or 4 DIMM’s along with any OC you may do.

Pretty sure one of the most important factors is the BIOS revision, many times updates will resolve not just compatibility issues with memory kits but also with any OC.

Mileage will vary of course.

The only benefit you’ll get after 3600 is bragging rights, there’s some good dual channel 32 gb kits 16 latency for a reasonable price … I don’t think you’ll see a noticeable benefit from anything faster than that…