ryzen Ryzen 5000 memory layout - 2x8GB vs 4x8GB vs 2x16GB - Single Rank vs Dual rank?

[SapphironZA]

Gamersnexus video on memory config with Ryzen 5000
I saw Steve from GN’s video( on some quite significant performance differences between 2x8GB and 4x8GB performance differences when using Ryzen 5000

They mentioned speaking to Wendell about it and he indicated that 2x16GB of single rank was the best config he has seen. He also mentioned interweaving playing a role (I don’t understand how).

I am curious as to the fundamentals impacting this. Without Wendel’s observation on 2x16GB, I would immediately assume that GN’s observation meaning that Dual Rank memory would be faster that single rank. but I also realized that its normally the opposite.

 

Should I stick with my 2x16GB memory order?
I have a 5950X with a Aorus Master X570 board and 2x G-skill Ripjaw 16GB 3600mhz CL16 memory on order.

 

I am doing a mix of IT, media and data production work and some nighttime gaming (usually grand strategy).

 

I would hate to leave performance on the table, since I am ordering all new parts. Also, if I need to upgrade to 4x 16GB RAM later, would I be seeing a drop in performance and should I rather go with 2x 32GB now?

Anyone else have some more information about this?

[Skiiwee29]

I would expect a deep dive video piece from gamers Nexus on this very subject in the next week. Its going to be a huge factor in performance and with the information starting to come out, hes going to want to jump on it while the iron is hot. I would wait until that comes out to make any purchase to get more in depth information. 

[SapphironZA]

1 minute ago, Skiiwee29 said:

I would expect a deep dive video piece from gamers Nexus on this very subject in the next week. Its going to be a huge factor in performance and with the information starting to come out, hes going to want to jump on it while the iron is hot. I would wait until that comes out to make any purchase to get more in depth information. 

Thx, that is the plan, but I was hoping someone might have seen other outlets already covering it

[Arrogath]

considering the I/O die is the same this generation as last there will be downsides to using very high capacity dimms, namely lower stable memory frequency with looser memory timings being necessary. If you are doing workloads that actually use large amounts of memory it may be a good idea to at least start with 2x16 gb so you can upgrade to 64 down the line if you find you need it. If you want a breakdown of memory bandwidth for a multitude of different memory setups Buildzoid from actually hardcore overclocking has a very well put together piece using the 3000 series processors that should still be relevant given the same memory controller on 5000

 

edit: from what I was seeing, dual rank was where performance seemed to stop climbing quickly with how difficult it was to get quad rank stable at fast speeds and tightish timings

[Mateyyy]

10 minutes ago, SapphironZA said:

2x16GB of single rank

2x16GB will be dual-rank.

16GB DDR4 sticks are dual-rank.

10 minutes ago, SapphironZA said:

Should I stick with my 2x16GB memory order?

Yes, I don't see why you wouldn't.

[porina]

Maybe I should start watching GN again... not kept up to date with the ongoing testing on Zen 3, but as a generalisation ram differences are relatively small in the overall picture. Unless you have a use case where every last drop of performance is really critical, then I wouldn't overly worry about it. About the only use cases where such ram consideration might be applicable are compute intensive tasks (if you dedicate a system 24/7 doing the same work, and want to optimise for it), and competitive benchmarking.

[SapphironZA]

2 minutes ago, porina said:

Maybe I should start watching GN again... not kept up to date with the ongoing testing on Zen 3, but as a generalisation ram differences are relatively small in the overall picture. Unless you have a use case where every last drop of performance is really critical, then I wouldn't overly worry about it. About the only use cases where such ram consideration might be applicable are compute intensive tasks (if you dedicate a system 24/7 doing the same work, and want to optimise for it), and competitive benchmarking.

Generally, I would agree with you, but in this case it does seem to make a 5-10% difference.  While spending double RAM might not seem worth it for 5-10%, when you are spending $1500+ on CPU, Board, 280mm AIO cooler and RAM, an extra $50 for 5-10%  is worth it.

[porina]

13 minutes ago, SapphironZA said:

Generally, I would agree with you, but in this case it does seem to make a 5-10% difference.  While spending double RAM might not seem worth it for 5-10%, when you are spending $1500+ on CPU, Board, 280mm AIO cooler and RAM, an extra $50 for 5-10%  is worth it.

Ok, now I remember why I stopped watching GN. I skimmed the video and may have missed stuff. To recap, Steve claims in talking with Wendell that 16GB single rank was best. his own testing with 8GB modules showed 4x8GB better than 2x8GB. I assume the 8GB modules are single rank as dual rank ones haven't been a thing for a very long time.

 

The overall clam at 8GB modules was that 4x8 was better than 2x8 by typically 8%, maybe 10% in more ram demanding workloads. This is very interesting to me, as I've seen similar on Zen 2 and Intel in compute workloads, but I never managed to show it in gaming in my very limited testing. Within the scope of my testing, I found 2 DIMMs per channel (DPC), or equivalently using one dual rank module per channel, with otherwise same speed and timings, there is an improvement over single rank/1DPC. In practical terms this seemed to be a tradeoff shown in synthetic benchmarks of increased effective bandwidth, at the cost of slightly increased latency. So how the application behaves depends on either may affect if there is a benefit or not. Rank interleave is a probably contributing factor, except when rank is not factor. There is a similar mechanism when running 2DPC.

 

The only 16GB modules I have are dual rank, so I've no experience of 16GB single rank modules. So back to your original question, there may or may not be something there depending on if the 16GB modules you're looking at are single or dual rank, but we don't have a comparison for that point. In my testing, 16GB dual rank module performance is within expectations of running lower capacity modules in 2DPC, or dual rank modules. So you'll probably be on the higher end. If 16GB single rank modules are even better, and by how much, we'll have to await further testing to tell.

[Arrogath]

4 minutes ago, porina said:

The only 16GB modules I have are dual rank, so I've no experience of 16GB single rank modules. So back to your original question, there may or may not be something there depending on if the 16GB modules you're looking at are single or dual rank, but we don't have a comparison for that point. In my testing, 16GB dual rank module performance is within expectations of running lower capacity modules in 2DPC, or dual rank modules. So you'll probably be on the higher end. If 16GB single rank modules are even better, and by how much, we'll have to await further testing to tell.

I would imagine the reason single rank 16 GB modules are better than dual rank is that when you run 4 of them you can maintain higher frequencies at agressive timings with all that extra memory

[porina]

3 minutes ago, Arrogath said:

I would imagine the reason single rank 16 GB modules are better than dual rank is that when you run 4 of them you can maintain higher frequencies at agressive timings with all that extra memory

Not going to rewatch but what I think I heard was that 2x16GB single rank was "best". That would possibly be a different mechanism than the one I saw using only 8GB or lower modules. Maybe there is something about high capacity chips that changes the way they are accessed, and that rank is not the significant factor, something else is.

 

Also I think to be fair when comparing configurations, the speed/timings should be kept constant. Speed and timings will provide extra variables to consider.

 

We need the test data to understand what is going on here for those seeking ultimate performance.

 

 

Forgot to mention before, the balance between CPU and ram isn't constant. Especially since Ryzen, the CPU potential has been increasing far faster than ram potential. Zen 3 being the overall highest performing core at the moment will be pushing the ram system harder, even with mitigations like L3 cache to try to take some load off it.

[Arrogath]

1 minute ago, porina said:

Not going to rewatch but what I think I heard was that 2x16GB single rank was "best"

you definitely heard right, it just sounded weird to me since most 16GB sticks are dual rank. Wendell may have been referring to the 4000 Mhz kit with 16 GB sticks that came out recently so it's hard to know exactly what is allowing for the performance benefit

[Jillorval]

There is a comment on the GN youtube video by Mirsad Redzovic that seems to explain everything