Please confirm/refute several statements about RAM

Coolio

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Hi guys,

I'm going to build my first PC and though I spend a lot of time to find out the details myself, I'll be grateful if you kindly help me to double-check several points with you.

Just in case: 99% that my future CPU will be AMD Ryzen 5000 [Zen 3]; I know what the Infinity Fabric and Coupled Mode are 🙂; my PC usage scenario is 50/50 (gaming/office)
  1. Single stick dual-rank RAM is faster than a single stick single-rank
  2. CPUs perform best when their memory controllers access to 2 ranks per channel (i.e. 4 ranks in total) and this can be achieved by 2 single stick dual-rank RAM modules
  3. Are there any requirements to the motherboard from the dual-rank RAM modules support perspective? I mean not the clock rate compatibility here, but the RAM dual-rank technology compatibility with MoBo.
  4. High-performance RAM uses factory overclocking feature (XMP profiles in BIOS). Is it true that both CPU and MoBo should support the MAX clock rate set in XMP (= Profile #2 settings)?
  5. To extend RAM lifetime is it possible (and does it make sense at all) to use middle-level profile (XMP Profile #1) for regular work (office apps, browser) and high-level profile (XMP Profile #2) for gaming?
  6. Addition to point #4: I've heard that the "MoBo clocks should be equal to those of the RAM" rule of a thumb was valid in the past, when RAM connected to CPU via the Front Side Bus/Northbridge Chipset. In modern days, when CPU/RAM are connected directly via QPI, this rule makes no sense, as MoBo automatically decreases RAM clocks (if they're too high) to those of MoBo itself or of the CPU (whichever MAX clock rate is lower). Is this true or the gossip?
Thank you guys and have a nice weekend!
 

ashmelev75

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1-3) don't bother too much about that. Single rank v vs dual rank difference is a few percent at most.
4) XMP profiles provided by manufacturer only depend on what they want to sell. Same physical chips can be soldered to modules with different XML profiles. As long as you're not trying something exotic like 6000MHz CL50 DDR4 why does it even matter?
5) Run the memory on standard DDR4 voltage and it will serve for decades. Using higher voltage may damage memory chips over time.
6) match DDR clock to Infinity fabric clock and you're fine, and even if you don't do that it is not a big deal
 

Coolio

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Spasibo, Mr. Shmelev! ;)

1-3) don't bother too much about that. Single rank v vs dual rank difference is a few percent at most.
Well, #1-2 I'll google more to see if there's (no) significant difference between "single/dual" rank RAM modules. However, #3 was about compatibility of components - I can't just not bother about that. Do you say there's no MoBo incompatibility issue with the "dual-rank" RAM technology itself?

Run the memory on standard DDR4 voltage and it will serve for decades. Using higher voltage may damage memory chips over time
#4-5 - honestly I've thought XMP (or DOCP or A-XMP - for AMD MoBos) was not overclocking, but smth. else. Taken that tons of YT videos demostrate that RAM overclocking makes almost no sense (as opposed to CPU overclocking!) I guess playing with XMP profiles won't significantly change productivity of my machine, so in this particular case it really makes sense not to bother. :)
 

ashmelev75

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Well, #1-2 I'll google more to see if there's (no) significant difference between "single/dual" rank RAM modules. However, #3 was about compatibility of components - I can't just not bother about that. Do you say there's no MoBo incompatibility issue with the "dual-rank" RAM technology itself?

#4-5 - honestly I've thought XMP (or DOCP or A-XMP - for AMD MoBos) was not overclocking, but smth. else. Taken that tons of YT videos demostrate that RAM overclocking makes almost no sense (as opposed to CPU overclocking!) I guess playing with XMP profiles won't significantly change productivity of my machine, so in this particular case it really makes sense not to bother. :)

Considering that
a) Dual rank modules are everywhere, there's no special support needed
b) You'll have trouble finding single rank DDR4 modules at any high capacity, most of them are just OEM trash
c) You are not going to use one single or one dual rank module in a computer (that's just silly)
you are focusing on issues that are not real. Two single rank modules, each on its own memory channel would be better than one dual rank module on a single memory channel, but two dual rank would be faster than two single rank modules.

SPD/XMP is just a table with timing and voltage profiles that always include some JEDEC ones (<=1200 MHz @ 1.2v or less and a few 'overclocking' ones (>1200MHz at >=1.35v). Higher clock modules usually have profiles for lower frequencies and better timings (example 3800 CL20 + 3600 CL18 + 3200 CL16). Usually those XMP profiles are quite loose and can be tightened down a few notches. Example is buying 3200 CL16 module and running it at 3600 or higher with the same CL16 and same voltage.
Ram overclocking does increase overall transfer rates, but that is not something you'll ever notice just by playing a video game. Some people don't even notice their fancy RAM is running at default JEDEC speeds for years.
 

Coolio

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You are not going to use one single or one dual rank module in a computer (that's just silly)
Never said I will. Taken I need 16Gb in total my choice is either 2x8Gb (dual-rank) or 4x4Gb (single-rank) and this is what I'm trying to clarify in this post.

you are focusing on issues that are not real
The choice I've mentioned above is the point of concern of hundreds of people - based on # of YT views and article reads on the "single vs. dual rank RAM" subject.

Single rank v vs dual rank difference is a few percent at most.
two dual rank would be faster than two single rank modules
Finally - faster, but only a few %?

Ram overclocking does increase overall transfer rates, but that is not something you'll ever notice just by playing a video game. Some people don't even notice their fancy RAM is running at default JEDEC speeds for years.
Well, you can live the whole life with VW Passat 2002 which doesn't mean you won't like Mercedec SLK 2020. Moreover, having watched several videos since my 2nd post I start to doubt XMP is not worth a try. It seems like the "rank" of priorities (from their effectiveness perspective) is the following:
  1. dual-channel config (we both totally agree with that, right?)
  2. locked in XMP profiles (speeds upped)
  3. dual rank RAM sticks
And they claim #1 + #2 cover 85% (roughly) of the result.

Higher clock modules usually have profiles for lower frequencies and better timings (example 3800 CL20 + 3600 CL18 + 3200 CL16).
Example is buying 3200 CL16 module and running it at 3600 or higher with the same CL16 and same voltage.
OK, let's assume I have a Ryzen 5000 (Zen3) which Inf.Fabric supports clocks up to 1900MHz, so DDR4 3733MHz is the best choice here (higher clocks will result in CPU unstability and latency issues - this is obvious). Assuming my MoBo supports XMP (DOCP, A-XMP - whatever we call it) what exactly can I do in my UEFI?
  1. Increase RAM clocks? No sense to jump over CPU IF's maximums, right?
  2. Decrease RAM clocks to gain better timings (20 -> 18 -> 16)? No much sense unless you run heavy tasks (e.g. several virtual machines), which is not a consumer usage scenario.
Finally, my verdict will be: clock rate faster XMP profiles make sense, but only if RAM's factory clocks are lower than CPU IF's clock maximums (I'm only talking of AMD here - haven't studied Intel, as it's beyond the scope of my interest). Please correct me if I'm wrong here.
 

ashmelev75

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Never said I will. Taken I need 16Gb in total my choice is either 2x8Gb (dual-rank) or 4x4Gb (single-rank) and this is what I'm trying to clarify in this post.

Performance-wise there will be no practical difference. One dual rank module on single memory channel operates the same way as two single rank module on a single memory channel. Better performance comes from two memory channels and memory controller being able to interleave the available memory.

So, buy two or four matching memory modules to get the RAM size you want. If you can afford more expensive and higher clocked modules, get those and tighten the timings, or buy cheaper modules and overclock them.
Some tasks benefit from higher throughput, some benefit from lower latency. With a mixed bag like yours, it does not matter much.
 

MaZa

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I disagree with the above statement that single rank and dual rank difference is just a few percent. It is actually quite noticeable and very measurable performance bump (if all other things are equal, speed and timings). However this is ONLY the case only if you are CPU limited. In 99% of the cases you are GPU limited in games unless you are gaming in low resolutions and quality settings.

Should you get 2 sticks of dual rank or 4 sticks of single rank, it makes no real difference. If you run 4 sticks of single rank kits in dual channel system then you are turning them into dual rank in function. So get what is the cheapest or if you feel that you need to have two empty slots for possible future upgrades.

And don't fret about XMP profiles and lifetime of the memory. If the memory fails, it is not because of the XMP but because the kit was faulty from the start. Some motherboards do not play nice with XMP profiles on some kits but if that happens then that is just shitty luck. If that happens then go manual and tweak the timings yourself.
 

Coolio

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Thank you for your input MaZa !

I disagree with the above statement that single rank and dual rank difference is just a few percent.
After investigating this topic for a while I came across such a characteristics as Rank-Per-Channel (RPC), which I supposed to help me in understanding of all this memory logic. Coming back to what you guys say:

Should you get 2 sticks of dual rank or 4 sticks of single rank, it makes no real difference.
2x2R DIMMs being placed in 2 slots (which make 1 channel) result in RPC = 4, right? Following this logic 4x1R DIMMs being placed in 4 slots (which make 2 channels) should result in RPC = 2, which from my understanding should be less productive than RPC4 architecture. This is aligned with what ashmelev75 said earlier:

One dual rank module on single memory channel operates the same way as two single rank module on a single memory channel.
But as a newbie I could have misunderstood this RPC concept, because in the way I took it the architecture you've mentioned below....

If you run 4 sticks of single rank kits in dual channel system then you are turning them into dual rank in function.
.... is definitely a dual channel one, however its RPC is = 2, which should be less efficient than RPC = 4 (2x2R DIMMs on 1 channel). Where am I wrong? :unsure:
 

ashmelev75

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I disagree with the above statement that single rank and dual rank difference is just a few percent. It is actually quite noticeable and very measurable performance bump (if all other things are equal, speed and timings).

On a single channel and only if you're using one module. 1R x 8GB module accessible as a whole at vs 2R x 8GB module which is 4GB + 4GB which can only be accessed one at a time.

Should you get 2 sticks of dual rank or 4 sticks of single rank, it makes no real difference. If you run 4 sticks of single rank kits in dual channel system then you are turning them into dual rank in function. So get what is the cheapest or if you feel that you need to have two empty slots for possible future upgrades.

And that exactly what I said. When you have two memory channels it does not mater what kind of module you're using. In some cases using 2R x 2 memory channels is better, but it depends on the memory controller utilizing it properly.
 

ashmelev75

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But as a newbie I could have misunderstood this RPC concept, because in the way I took it the architecture you've mentioned below....

If your still confused look at that like this:

In your right hand you're holding a sheet of paper with something written on the front of it. That is a single memory channel with a single rank memory module. You can read what is written on the sheet easily without any issues.
Now imagine you're holding twice as small sheet where the content is written on both front and back. Same amount on content, but to read it all you need to flip the sheet to access it back side and that takes some effort and time and you can't access all the text at the same time.

Now imagine you're holding the same small sheets in both right and left hands. You have the same block of text, but it is distributed between left and right sheets - half on one and half on the other. You can read both at the same time without any issues, no page flipping is required.
 

Coolio

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ashmelev75 great explanation with sheets of paper, really! You won't believe but I just found out that my key mistake was that RPC should be concentrated in 1 channel if there are 2 DIMMs, while the idea is to distribute RPC across channels. So if I have channels A and B represented by slots A1, A2, B1, B2 and 2 DIMMs I need to plug them to A1 and B1, not to A1 and A2 like they write in some articles. This is what made all the situation so weird and me looking like a total dumb-ass.
Thank you for your patience guys, that was something. 🙄

I know there are some peculiarities in memory frequency in relation to whether DIMM is 1R or 2R. Like 1R has 8 chips/banks and higher clocks, while 2R has 16 chips and lower clocks.
Ryzen 5000 Infinity Fabric supports DIMMs up to 3733MHz, so I can buy either 4x8Gb 1R 3733MHz or 2x16Gb 2R 3200MHz. Which will be better and why?
 

ashmelev75

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So if I have channels A and B represented by slots A1, A2, B1, B2 and 2 DIMMs I need to plug them to A1 and B1, not to A1 and A2 like they write in some articles.

Actually read the manual. A1 and A2 slots can be on different channels, that is why some articles say that.

I can buy either 4x8Gb 1R 3733MHz or 2x16Gb 2R 3200MHz. Which will be better and why?
Look.. just buy this https://www.amazon.com/Crucial-Ballistix-Desktop-Gaming-BL2K16G32C16U4B/dp/B083TSLDF2
and tune the timing to 3733 CL16 and be done with it already.
 

BinarySynapse

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.
Like 1R has 8 chips/banks and higher clocks, while 2R has 16 chips and lower clocks.
A rank is 64-bits wide (72 for ecc). Chips that have 8 data lines (x8) require 8 chips to fill a rank. So 16 chips would indeed be two ranks.

However x4 chips would need 16 chips for just one rank, and x16 chips need only four.

(BTW, Bank is a similar term, but applies either to a chip’s internal configuration or the memory subsystem as a whole. Rank, while functionality the same as a bank to the system, refers only to a module’s configuration.)
 

ashmelev75

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This is 3200, they have a 3600 model too. Is there any benefit except price to buy lower clock DIMMs and overclock them vs. buying higher clock DIMMs and not bother with overclocking?
Most of the time it is exactly the same memory chips, just with an extra profile programmed for 3600 speed and loose timings.
You pay extra $40 for a small guarantee that the modules would work at stated speed. In reality the XMP profile flashed into those modules is quite loose. You can easilly tune 3200CL16 down to CL14 or up to 3600CL16 just by raiding the DDR clock.

Higher clocked modules are another story. Usually they have to be hand-picked and assembled from the chips cut out of middle of the wafer and programmed with maximum allowed voltage and very very loose timings.
Ballistix 4400MHz comes with 1.4v and 19-19-19-46 timings
Ballistix 5100MHz comes with 1.5v and 19-26-26-48 timings
 

Coolio

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Most of the time it is exactly the same memory chips, just with an extra profile programmed for 3600 speed and loose timings.
You pay extra $40 for a small guarantee that the modules would work at stated speed
Higher clocked modules are another story. Usually they have to be hand-picked

Well I'd better save $40 - my case will probably cost $200-250, so $40 will matter a lot. And looks like overclocking RAM is not that hard if done carefully.
How do I know "regular" RAM, from "pseudo-fast" (XMP-profiled) and from "binned" (top) models? Can this distinction be traced from the clock rate or...?
 

ashmelev75

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How do I know "regular" RAM, from "pseudo-fast" (XMP-profiled) and from "binned" (top) models? Can this distinction be traced from the clock rate or...?

Depending on the manufacturer. There are top tier ones that use their own chips to make modules, such as Crucial using Micron chips.
There are second tier manufacturers, such as Kingston, G.Skill and others, buying cheap untested wafers from Samsung, Hynix and cutting/grading chips in house in order to make profit.

Essentially all 2600-5100MHz chips are cut from the same wavers, some chips end up better quality and are hand picked for mode expensive modules. See filet mignon vs ground beef trimmings.

You can guess the grade by looking at speed, timings and voltage.
The lower the timings for the same speed and voltage, the higher the chance that it was actually graded / tested. From better to worse:
3200CL14-14-14-34
3200CL16-16-16-36
3200CL16-18-18-38
3200CL18-19-19-42

Peformance-wise there's little difference between these outside of benchmarking.

Edit:
The wafer quality has improved significantly over years, I would not be surprised if I find out that Samsung slaps the excess of their prime grade b-die chips on some OEM memory modules labeled as 2666MHz.
 
Last edited:

Coolio

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There are top tier ones that use their own chips to make modules, such as Crucial using Micron chips.
As I know each DIMM has 2 clock rates: the "base/factory" one (e.g. 3200) and the max. guaranteed by manufacturer as bug-less (e.g. 3733). One can overclock them further of course, but it's another story. Is there any sense to buy DIMMs from top-tier manufacturers if I want to run them only at max. guaranteed speed (i.e. 3733) and do no further overclocking? Or any reputable brand (Kingston, etc.) will be fine for this scenario?

From better to worse:
3200CL14-14-14-34
3200CL16-16-16-36
3200CL16-18-18-38
3200CL18-19-19-42
OK, this I understand, but let's assume these are "factory" clocks, while the "max. guaranteed" by the manufacturer is 3733. Am I right the first one will be the best choice, as based on its timings (14-14-14-34) this must be a binned chip, so it will handle overclocking to 3733 better than others from this list. Is that correct?
 

ashmelev75

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OK, this I understand, but let's assume these are "factory" clocks, while the "max. guaranteed" by the manufacturer is 3733. Am I right the first one will be the best choice, as based on its timings (14-14-14-34) this must be a binned chip, so it will handle overclocking to 3733 better than others from this list. Is that correct?
I have Ballistix stick 3200CL16 running at 3800CL16 just fine.
 

Coolio

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ashmelev75 Damn, I won't sleep if I don't know the answer to the last question. This is surely one of the RAM cornerstones.

Your post clearly and persuasively explains the benefits of 1R vs. 2R DIMMs in terms of time needed to access data. It also confirms the statement "1R is faster than 2R, as when a computer accesses memory it only has to go around the track once vs. twice".

Today I've came across the article which says "the reason why dual-rank is faster is very simple, RAM (Random Access Memory) only does two things: It is accessed and it is refreshed, and one memory rank can only handle one of those operations per cycle. However, when a single stick has two ranks, one rank can be accessed while the other is being refreshed, and this is called Rank Interleaving. Most CPUs perform best when their memory controller has access to two ranks per memory controller channel or four ranks in total. Now this can either be done with two dual-rank modules or you can achieve the same rank interleaving by using four single-rank modules.".

You've also mentioned interleaving, but in relation to channels (which at some moment at last 🙄 became clear to me), while the guy talks about channels and (!) modules.

Finally, until today I thought that 2x1R in 2 channels are faster than 2x2R in 2 channels, as while the main goal (2 channels) is reached in both cases, the former config allows to "go around track once vs. twice. However, the guy says it's crucial that those 2 sticks are 2R - to activate Rank Interleaving tehcnology. Where the truth here? 😕
 

ashmelev75

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this can either be done with two dual-rank modules or you can achieve the same rank interleaving by using four single-rank modules.".

As it was said 4 times before. You're not going to buy a single stick of RAM, so why this confusion and dancing around? Buy a kit of two 2R modules (or a kit of four 1R modules) and put them on different channels. Done and done.
 
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