Question Single/dual channel, Single/dual rank and XMP - clarification needed

Jan 8, 2021
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Hi guys,

I've read quite a lot on the topic, but will also appreciate if you share your expertise. I am going to buy AMD Ryzen 5000 (Zen3) CPU and 16Gb of RAM.

After hours of research I came to the conclusion that the factors which have direct impact on memory performance can be ranked as follows:
  1. dual-channel config (i.e. 2x8Gb is better than 1x16Gb)
  2. locked in XMP profiles (called DOCP/A-XMP profiles in my "AMD scenario"), i.e. RAM speeds upped
  3. dual rank RAM sticks
Moreover, as far as I understand #1 + #2 are responsible for 85% (roughly) of the final result.

With all the above-mentioned considered and taken that Zen3's Infinity Fabric (IF) supports clocks up to 1900MHz, DDR4 3733MHz 2x8Gb seems to be the best choice (higher clocks will result in CPU unstability and latency issues). However there are some questions:
  1. Am I right that with DDR4 3733MHz I only have to secure via XMP menu that my RAM clocks are not below 3733MHz - in other words I only have to ensure the factory clock speed is achieved? My assumption is that "speeding up" RAM would have made sense if my RAM clocks were below (e.g. 3200MHz) the maximum supported by CPU, but as 3733MHz is that very maximum supported by Zen3's IF - there's no sense to go above factory clocks. Is that correct?
  2. Haven't compared prices for single/dual rank RAM modules yet, but based on YT videos dual-rank modules show more or less significant advantage in file copying only. Am I right there's no much sense to overpay for dual-rank modules unless I move huge amounts of data on a regular basis?
  3. MoBo should support RAM/CPU clock rates (this is obvious), but there are no specific requirements to MoBo from the dual-rank RAM module perspective (i.e. all MoBos support dual-rank RAM sticks), correct?
Thank you for sharing your thoughts!
 
so... for best ram performance u need 2 sticks for dual channel that is correct
they need to be single sided (1R - 1 rank), as 2R rams are faster, but put more strain on memory controller, which results in lower overclock then with 1R modules (two 2R sticks are about same as 4 single sided sticks running in dual channel, ram bandwith is much higher thanks to memory interleaving, memory interleaving need either 2 dual rank stick or 4 single rank sticks - btw almost zero difference for gaming)

3733MHz isnt limit for ryzen 5000, thats limit for infinity fabric, infinity fabric runs at same clock as your ram, u can with ryzen 5000 make it half speed of your ram speed for further ram overclock (but ull get worse performance if u do that)

as for XMP, its a overcloking profile, factory preconfigured ram settings which that stick can handle.
XMP will not work with every mainboard, you should always check memory support page for ram QVL list
in this list u can see RAM modules which were tested, and it also contains how many sticks u can use and max ram speed with XMP settings, make sure u select corret mainboard and correct CPU for QVL list.
u can also check RAM maker web page to find sticks u like, they also should have QVL list for supported mainboards with those sticks (not all ram makers have it)
 
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Jan 8, 2021
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Thank you @kerberos_20 !

I did some research and came to the conclusion that 1R/2R is not only the technology (with physical chips being on 1 or 2 sides of the RAM stick), but also the architecture, where 4 1R sticks being placed in 4 slots (which form 2 channels, e.g. 2 green slots = channel #1, 2 black slots = channel #2) shape the same 2 rank construction as 2 2R sticks placed in 2 slots (of the same channel of course!).

Is that right? What about 4 2R sticks in 4 slots/2 channels - shall they push the productivity even further? (capacity in Gb will be higher, this is obvious)

2R rams are faster, but put more strain on memory controller
Taken that my system will be AMD-based, what are the risks of this strain and under which scenarios?
 
Thank you @kerberos_20 !

I did some research and came to the conclusion that 1R/2R is not only the technology (with physical chips being on 1 or 2 sides of the RAM stick), but also the architecture, where 4 1R sticks being placed in 4 slots (which form 2 channels, e.g. 2 green slots = channel #1, 2 black slots = channel #2) shape the same 2 rank construction as 2 2R sticks placed in 2 slots (of the same channel of course!).

Is that right? What about 4 2R sticks in 4 slots/2 channels - shall they push the productivity even further? (capacity in Gb will be higher, this is obvious)
using 4 dual rank rams wont give u any benefit on dual channel ram controller (only more ram benefit)
switching to tripple/quad/etc channel is another matter (hedt/server platforms)

Taken that my system will be AMD-based, what are the risks of this strain and under which scenarios?
well that strain means, ram may not work (system wont boot or half ram hardware reserved)
for ram compatibility u should check mainboard QVL list for supported rams, theres differences in that list based on cpu selected (as AMD is still refining mem controller each gen they produce)
and between mainboards there may be some differences aswell as they have differences in traces between dim slots and cpu

as for your question about amd support on 4 dual ranked slots
example rog crosshair VIII dark hero lists those sticks under 5000 series as compatible
https://www.amazon.com/HyperX-Black-3600MHz-HX436C18FB3K4-128/dp/B089QSL19K
so i guess 5000 serie chips have decent ram controller (as those rams have micron chips and not samsung b-die)
 
Jan 8, 2021
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@kerberos_20 Thank you dude!

In order to summarize:

Regardless of the fact that...
i guess 5000 serie chips have decent ram controller
Still...
using 4 dual rank rams wont give u any benefit on dual channel ram controller
Is that right?

those rams have micron chips and not samsung b-die
Good point. Are Micron-based DIMMs in general better than Samsung-based ones? I mean regardless of 1R/2R/1ch/2ch/whatsoever topic?

well that strain means, ram may not work (system wont boot or half ram hardware reserved)
for ram compatibility u should check mainboard QVL list for supported rams
Sorry, but it's still not clear whether the 2R "puts more strain on memory controller" is the conceptual problem (= 2R puts strain. Period.) or this is the problem of compatibility (= 2R puts strain only on unsupported MoBos)? Possibly my bad, but I can't read your message clearly from this perspective.
 
Good point. Are Micron-based DIMMs in general better than Samsung-based ones? I mean regardless of 1R/2R/1ch/2ch/whatsoever topic?
hmm not really, samsung usualy provides better overclock with lower latencies
but if u compare micron e-die dual rank vs samsung b-die single rank, then u get about same speed there

Sorry, but it's still not clear whether the 2R "puts more strain on memory controller" is the conceptual problem (= 2R puts strain. Period.) or this is the problem of compatibility (= 2R puts strain only on unsupported MoBos)? Possibly my bad, but I can't read your message clearly from this perspective.
think of it like this, ram controller is piece of hardware which has its own physical limits
1R has 8 chips (banks)
2R = 16 chips
2sticks 1R = 16chips
2sticks 2R = 32 chips
4sticks 1R = 32chips

more chips = more power ram controller has to provide to keep it stable, which can be corrected with voltages/resistances...but there are physical limits what that controller can provide (max voltage/resistances u can set before blowing it up) and also some mainboards doesnt like it when u overvolting (4layered mobos)
so u can mix:
low amount of banks x high speed and low latencies
low amount of banks x even higher speed at higher (slower) latencies
high amount of banks x lower speed than u can get with lower amount of banks

well it depends on ram controller what it can provide, thus looking at mainboard QVL list for said cpu serie
that gives rough idea on what u can expect from it, and said ram will work without fiddling with bios settings to make ram stable
 
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If you are just looking for information on what ram kit to buy for Ryzen 5000, you should just get 2x16GB 3600 CL16-19-19 for a decent balance between price, performance and capacity. That's assuming you need 32GB of ram now or in the future, otherwise cheaper 2x16GB 3600 CL18 will be fine.

If you happen to get 2x8GB and then another 2x8GB later, you will probably still be able to run 4x8GB 3600 CL16 with Ryzen 5000, but mixing kits is not recommended and may force you to run at 3200. The majority of users won't even notice the difference between 3200 and 3600 unless benchmarking, so don't over think it.
 
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Thank you @kerberos_20 ! That's a good thing you've explained about chips/banks - it clearly shows why 2x2R is equal to 4x1R. (y)
Taken that I need 32Gb built from one of those 2 variants, do my examples below correctly depict the logic of your 3 scenarios?

so u can mix:
low amount of banks x high speed and low latencies 4x8Gb 1R 3600MHz
low amount of banks x even higher speed at higher (slower) latencies 4x8Gb 1R 3733MHz
high amount of banks x lower speed than u can get with lower amount of banks 2x16Gb 2R 3200MHz
As my CPU will be Ryzen 5000, which Infinity Fabric supports up to 1900MHz clocks I was strongly focused on buying a 3733MHz DIMMs (don't want to bother with overclocking). Based on what you've said looks like I can't have (or better not have) this frequency in 2x16Gb 2R version...? :confused_old: I'm sorry to possibly look dumb, but RAM turned to be much more complicated (unexpectedly!) topic to me that MoBo and CPU together.

The majority of users won't even notice the difference between 3200 and 3600 unless benchmarking, so don't over think it.
@Third-Eye Thank you for your input and recommendation on the exact model - appreciate that. I just want to understand principles themselves to be able to help others and not bother forum folks next time I need upgrade. :)
 
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You won't believe folks, but initially I supposed the goal is to concentrate RPC (rank per channel), while in fact it is to distribute RPC across channels so that all the channels are active - regardless of whether DIMMs are 1R or 2R.
So if my MoBo has 2 channels (A and B) presented by 4 slots (A1, A2, B1, B2) and I have 2 DIMMs I need to plug them to A1 and B1 - so that both channels are active. If I have 4 DIMMs I plug them to all 4 slots. There are so many articles which say to plug 2 DIMMs in A1 and A2, which made me 100% sure this is the right way - load 1 channel @ max and that's it!

I hope this is finally correct . I feel so stupid. :LOL:
 
You won't believe folks, but initially I supposed the goal is to concentrate RPC (rank per channel), while in fact it is to distribute RPC across channels so that all the channels are active - regardless of whether DIMMs are 1R or 2R.
So if my MoBo has 2 channels (A and B) presented by 4 slots (A1, A2, B1, B2) and I have 2 DIMMs I need to plug them to A1 and B1 - so that both channels are active. If I have 4 DIMMs I plug them to all 4 slots. There are so many articles which say to plug 2 DIMMs in A1 and A2, which made me 100% sure this is the right way - load 1 channel @ max and that's it!

I hope this is finally correct . I feel so stupid. :LOL:
sure, dual channel just need 2 sticks in order to run in dual channel, no matter rank
btw it is A2 + B2 slots if mainboard has 4 slots on both intel and amd
 
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btw it is A2 + B2 slots if mainboard has 4 slots on both intel and amd
Thank you! I hope there will be instructions in the MoBo manual too.

2R rams are faster, but put more strain on memory controller ... that strain means, ram may not work (system wont boot or half ram hardware reserved)
more chips = more power ram controller has to provide to keep it stable, which can be corrected with voltages/resistances
there are physical limits what that controller can provide (max voltage/resistances u can set before blowing it up) and also some mainboards doesnt like it when u overvolting (4layered mobos)
Does all that mean, that there's no need to check if MoBo supports this particular 1R DIMM module, while it surely makes sense to check its compatibility with 2R DIMM of the particular model? I'm not talking about overclocking here - just about buying DIMM which factory clocks are within the limits supported by Infinity Fabric.
 
Thank you! I hope there will be instructions in the MoBo manual too.
it should be there ;)

Does all that mean, that there's no need to check if MoBo supports this particular 1R DIMM module, while it surely makes sense to check its compatibility with 2R DIMM of the particular model?
if u buy sticks not listed in QVL, then u may get compatibiity issues (as they werent tested on that mainboard)

I'm not talking about overclocking here - just about buying DIMM which factory clocks are within the limits supported by Infinity Fabric.
most ram sticks u buy have base clock at 2133~2400MHz,
they have XMP profile to get them to advertised speeds which is overclock
cpu specs for ryzen 5000 is advertised as "ram support up to 3200MHz", which means, setting up xmp profile while reducing ram clock to 3200 = no overclock
going past that = overclock

mainboard specs usualy tells that aswell... for example dark hero mainboard:
AMD Ryzen™ 5000 Series/ 3000 Series Desktop Processors
4 x DIMM, Max. 128GB, DDR4 4866(O.C)/4800(O.C.)/4666(O.C.)/4600(O.C)/4400(O.C)/4266(O.C.)/4133(O.C.)/4000(O.C.)/3866(O.C.)/3733(O.C.)/3600(O.C.)/3466(O.C.)/3400(O.C.)/3200/3000/2933/2800/2666/2400(O.C.)/2133 MHz Non-ECC, Un-buffered Memory
tho im not sure why 2400 is considered there as oc
AMD RyzenTM 2000 Series Processors
4 x DIMM, Max. 128GB, DDR4 3600(O.C.)/3466(O.C.)/3400(O.C.)/3200(O.C.)/3000(O.C.)/2933/2800/2666/2400/2133 MHz Non-ECC, Un-buffered Memory
heres for ryze 2000 with support up to 2933MHz, clockin above (even if we know cpu can handle it) is overclock


so, if u stick with QVL and search for ram there, u will know which ram will be plug and play and will work just like that
if u buy sticks not listed there, u may have issues with clocking them to advertised speeds, or maybe just 2 sticks from 4 will work...or it may work fine as there are plethora of rams while theres no way to test them all
 
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most ram sticks u buy have base clock at 2133~2400MHz,
they have XMP profile to get them to advertised speeds which is overclock
So if I see DIMM is 3700, this isn't its default speed, but the overclocked one, however this speed is guaranteed by the manufacturer to work without bugs, right?

cpu specs for ryzen 5000 is advertised as "ram support up to 3200MHz", which means, setting up xmp profile while reducing ram clock to 3200 = no overclock
going past that = overclock
I can't remember the article (if I find it I will post it here), but the sweet spot for Ryzen 5000 is 4000. After that latencies start. This is the reason why I've chosen 3733 as the best possible clock rate in my particular case.
 
So if I see DIMM is 3700, this isn't its default speed, but the overclocked one, however this speed is guaranteed by the manufacturer to work without bugs, right?


I can't remember the article (if I find it I will post it here), but the sweet spot for Ryzen 5000 is 4000. After that latencies start. This is the reason why I've chosen 3733 as the best possible clock rate in my particular case.
The advertised frequencies and timings are only certified to work with that kit by the manufacturer and whether it works with your motherboard and CPU is another matter. For Ryzen 1000-3000 CPUs and 300/400 series motherboards, you would need to research the potential issues with using higher frequencies so you can either pick a different motherboard or a different ram kit.

For most users, Ryzen 2000 tops out at 2x8GB 3400-3466MT/s, Ryzen 3000 2x8GB 3733-3800 and Ryzen 5000 should be able to reach 2x8GB 4000MT/s, though I've read about many people having issues going over 3866 with 1:1:1 ram to memory controller to Infinity Fabric frequency. I forgot where I read it, but there is suppose to be a bios update coming soon for 500 series motherboards to fix Infinity Fabric, so it runs stable at 2000Mhz with 4000MT/s ram.
 
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I can't remember the article (if I find it I will post it here), but the sweet spot for Ryzen 5000 is 4000.
@Third-Eye Sweet spot is exactly 3733 (I wrote 4000 - my bad!). Here is the screenshot from this article:



there is suppose to be a bios update coming soon for 500 series motherboards to fix Infinity Fabric, so it runs stable at 2000Mhz with 4000MT/s ram.
Well, I'm a noob in these things so far, but looks like there will be latency with 4000 clocks, no?

By the way, which module will you buy if on the one hand you want to overclock to get 3733, but on the other hand you want to save a bit money: will a 3200 be your choice or other? Which timings/latency and why?
 
@Third-Eye Sweet spot is exactly 3733 (I wrote 4000 - my bad!).

Well, I'm a noob in these things so far, but looks like there will be latency with 4000 clocks, no?

By the way, which module will you buy if on the one hand you want to overclock to get 3733, but on the other hand you want to save a bit money: will a 3200 be your choice or other? Which timings/latency and why?
Not many games will benefit from faster ram and are likely to only gain 10-20 fps at 3800-4400 CL18-CL20 compared to 3200 CL14 or 3600 CL16 on Intel or Ryzen systems. Most games just don't really take advantage of speeds over 3600 with CL16 timings and the additional cost of the faster ram with tighter timings is not really worth it for only 10fps in most cases. So for most users right now, 2x16GB 3600 CL16 is the just about the "middle ground" and "sweet spot" of good capacity, good speed and good pricing with enough ram for future games and programs.

The only reason I would consider ram faster than 3600 CL16 is if I have production work and other work-loads that are memory sensitive and run better with faster ram. In those cases though, I might also need more than 32GB, which drives up the cost even more for faster ram and could possibly force me to run an Intel system if I need faster ram than Ryzen 3000/5000 or Threadripper can handle.
 

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