4x single ranked dimms vs 2x dual ranked vs 4x dual ranked on Z370 platform?

From my understanding, 4x single ranked dimms in a dual channel setup should be identical to 2x dual ranked dimms? Wouldn't the 4x dimms overclock better due to less signal interference though? Since each rank of memory has its own dedicated set of traces to the IMC.

Another thing: shouldn't 4x dual ranked dimms provide the max bandwidth? Or are there too many ranks and switching around all the time causes a performance hit?

I'm trying to figure out whether it's better to use 4x 8GB samsung B-dies or 2x 16GB. I don't plan on upgrading past 32GB so the empty slots won't matter.

Thanks in advance!

There are limits of ranks on 2 channel boards. Regardless if you use 2x dual rank, 4x dual rank or 4x single rank then max bandwidth ( in programs that can use it ) will be the same. However, dual rank memory is overclocking worse but the same 4 memory modules overclock worse. Still 4 single rank modules should overclock higher as long as your motherboard is good.
Good 2x16GB will make ~3600 C16 at 1.35V. 4x8GB will make 4000 at 1.35V but there are other factors that affect stability so it's never guaranteed. There are 4x8GB 4266 kits too but on most motherboards they won't work.

Woomack said:

There are limits of ranks on 2 channel boards. Regardless if you use 2x dual rank, 4x dual rank or 4x single rank then max bandwidth ( in programs that can use it ) will be the same. However, dual rank memory is overclocking worse but the same 4 memory modules overclock worse. Still 4 single rank modules should overclock higher as long as your motherboard is good.
Good 2x16GB will make ~3600 C16 at 1.35V. 4x8GB will make 4000 at 1.35V but there are other factors that affect stability so it's never guaranteed. There are 4x8GB 4266 kits too but on most motherboards they won't work.

Click to expand...

Thanks for the reply but there seems to be some contradicting info out there regarding single ranked interleaving. According to this article: http://frankdenneman.nl/2015/02/20/memory-deep-dive/

Rank interleaving is disabled when any single ranked dimm is installed in that memory channel. So 4x single ranked dimms in a dual channel setup will not get any rank interleaving bandwidth boost?

I can't be sure generally, but in my ram limited compute cases, running 4x SR modules over dual channels gives the same performance boost as 2x DR modules in dual channel. Both of those cases are significantly faster than single rank dual channel. Having 2 rank per channel seems to give the benefit regardless if it is arranged in one or two modules. I haven't tested above 2 rank per channel.

In tests, results using 4x single rank modules and 2x dual rank are about the same. It's based on various benchmarks. However many programs run as fast on single rank as on dual rank memory. For instance barely any game runs faster on dual rank memory. In benchmarks you can see higher bandwidth in memory copy but Windows calculates memory performance based on memory copy as I noticed ( if you run winsat mem command then results are close to what AIDA64 is showing as memory copy ).

Personally I would get 2x16GB 3200 CL14-14-14 or CL15-15-15 as these kits are always good and let to OC at least up to 3600-3733 at low timings. Right now I'm using 4x16GB on X299 at 3733 17-17-17 1.35V.

On server boards I've seen dual rank as fast as quad rank but octa rank was slower than dual/quad.

Omegaboost said:

Thanks for the reply but there seems to be some contradicting info out there regarding single ranked interleaving. According to this article: http://frankdenneman.nl/2015/02/20/memory-deep-dive/

Rank interleaving is disabled when any single ranked dimm is installed in that memory channel. So 4x single ranked dimms in a dual channel setup will not get any rank interleaving bandwidth boost?

Click to expand...

the article you linked does not say that you dont get the benefits of rank interleaving if you use single ranked dimms. it says you dont get the benefits if you MIX dimms of different rank. its saying dont throw single rank dimms in with dual or quad ranked dimms. 4 single rank dimms is exactly the same as 2 dual rank dimms except one or the other might overclock better or worse.

i know this is an old thread but i found it looking for info and i thought it was worth appending to the thread

TLDR: Given the same memory clock speed and total capacity, in a dual channel setup 4 single rank DIMMs will result in the same performance as 2 dual rank DIMMs.

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When you introduce overclocking into the equation, people have always argued that 1 DIMM per channel is the best. 2 DIMMs for dual channel and 4 DIMMs for quad channel. Though it didn't seem like anyone really knew why.

For a given CPU/Motherboard chipset there is a specified limit to the number of ranks per channel before memory speed needs to be reduced. 2 Examples just because I happened to be looking at them recently:

--Intel Xeon E5-2600 v2 CPUs support DDR3 1866/1600MHz, but if you install more than 4 ranks per channel then only 1066Mhz memory clock speed is supported.

--AMD Ryzen 7 X370 setup supports 2667MHz DDR4 with one single rank DIMM, but that supported speed is reduced down to 1866MHz with two dual rank DIMMs per channel. Though AMD seems to be quite conservative with memory speed limits since it seems that people still hit 2400+MHz regardless of ranks.

So increasing the number of ranks can limit your higher memory clock speed. The inverse of that would be that fewer ranks could increase the the clock speed limit of your memory.

So if you're overclocking it makes sense to stick to the fewest # ranks per channel.

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Single rank DIMMs with 2 DIMMs per channel gives you 1 way rank interleaving. Dual Rank DIMMs with 1 DIMM per channel gives you 1 way rank interleaving as well.

2way rank interleaving (2 Dual Rank or 4 Single Rank DIMMs per channel) supposedly only gives you 5-10% increase in memory performance over 1way rank interleaving.

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Since a 10-40% drop in memory speed would quickly overshadow a 10% gain from rank interleaving, your better off getting fewer ranks if it allows your memory to run at a higher speed.

All this boils down to -> Get at least 1 DIMM per channel and limit the # of ranks per channel to where it doesn't reduce the memory speed you want to run.