Single Vs Dual Rank Memory

[AGTDenton]

Yesterday I loaded CPU-Z to get the model/spec of my RAM for the Cinebench results, as Corsair don't display the model or spec in their own software

Whilst flicking through the RAM slots in CPU-Z I noticed a couple of differences despite the part number being identical.



The first is the DRAM manufacturer differs between kit and secondly the Ranks configuration is different.

I'm curious as to whether there would be any real world performance differences.

This site is quite useful in covering the basics of single & dual rank RAM, however, it doesn't cover what happens when mixing ranks.
https://history-computer.com/single-vs-dual-rank-ram/

I can't find anything concrete as to what performance gains or losses I might incure.
There's just a mixture of comments on various forums that either say it's fine or others complaining of stability issues. No mention of any performance related info.

I bought the RAM (2x 32GB Kits) 3 months apart so some supply changes occured during that time.

I'm not in anyway worried or think I should run out the door to replace my RAM any time soon, I have no known stability issues.

[ik9000]

So, firstly, corsair advise you to check 3 different codes on their RAM sticks to check for a true match:


Single vs dual rank do behave differently SFAIK. In simple terms (which is as good as I understand it) it's to do with how the data goes along the pipeline with dual rank addressed in two lines rather than one. This is crucial's attempt to explain it: https://www.crucial.com/support/arti...-a-memory-rank

Which is better depends on your motherboard and CPU. I think Ryzen has a marginal boost with dual rank, but not enough to really matter in real world usage. Single rank is liked by extreme overclockers as it is said to give better stability when you crank it.

As to how SR and DR behave when paired? It will be down to how well the controller handles it. Presumably you need to ensure the SR and DR modules are paired together or the channel won't function. I think most modern mobo can handle SR and DR in independent channels and still provide dual channel mode.

[DanceswithUnix]

I noticed a couple of differences despite the part number being identical.

I've pretty much given up on Corsair ram at this point, they just seem too lucky dip.

Anyway...

If I'm reading this right, you have 4 sticks of ram in there? So if you started with 2 sticks, and they went into DIMM slots A2 and B2 like the manual says, and then you filled in the gaps when you bought the extra 2 DIMMs then the BIOS should be happy with that and configure itself optimally. A memory benchmark should show if you are getting interleaving, though frankly with modern multi core machines I'm not sure that really matters as there is always something for a memory channel to do.

What you are doing shouldn't be any more mismatched than, say, having a pair of 8GB sticks and then adding a pair of 16GB sticks, and that sort of thing happens all the time.

[AGTDenton]

I've pretty much given up on Corsair ram at this point, they just seem too lucky dip.

It does seem that way! Interesting, I'd have not thought to check prior to today simply because previously I would have bought say 16GB to replace 8GB and usually so much time had passed that the original model would not have been available to pair the original 8GB. I'd also never have expected configuration differences within the same part number, different DRAM chip manufacturers yes, but not different ranks.

If I'm reading this right, you have 4 sticks of ram in there? So if you started with 2 sticks, and they went into DIMM slots A2 and B2 like the manual says, and then you filled in the gaps when you bought the extra 2 DIMMs then the BIOS should be happy with that and configure itself optimally. A memory benchmark should show if you are getting interleaving, though frankly with modern multi core machines I'm not sure that really matters as there is always something for a memory channel to do.

You're correct, I should have made that clearer in the first post I have 4 sticks of 16GB as two 32GB kits. I'd bought 32GB (2x16GB) in roughly August then decided to get a further 32GB (2x16GB) in November. And yes installed the first 2 as one pair into A2 & B2 and the second pair into A1 & B1.

What you are doing shouldn't be any more mismatched than, say, having a pair of 8GB sticks and then adding a pair of 16GB sticks, and that sort of thing happens all the time.

Sounds logical to me.

So, firstly, corsair advise you to check 3 different codes on their RAM sticks to check for a true match:
[image...]

Single vs dual rank do behave differently SFAIK. In simple terms (which is as good as I understand it) it's to do with how the data goes along the pipeline with dual rank addressed in two lines rather than one. This is crucial's attempt to explain it: https://www.crucial.com/support/arti...-a-memory-rank

Which is better depends on your motherboard and CPU. I think Ryzen has a marginal boost with dual rank, but not enough to really matter in real world usage. Single rank is liked by extreme overclockers as it is said to give better stability when you crank it.

As to how SR and DR behave when paired? It will be down to how well the controller handles it. Presumably you need to ensure the SR and DR modules are paired together or the channel won't function. I think most modern mobo can handle SR and DR in independent channels and still provide dual channel mode.

Thanks useful information there. Though I'm not sure it buys anyone anything because you can't confirm it on the site you're buying from. As DWU points out, it's pot luck!
They'd be better off having a different part number.

[ik9000]

Thanks useful information there. Though I'm not sure it buys anyone anything because you can't confirm it on the site you're buying from. As DWU points out, it's pot luck!
They'd be better off having a different part number.

You'd think they'd just use a new part number wouldn't you. Problem is Corsair (and I imagine others but we know Corsair do it) regularly swap the memory chips presumably depending on what they can get for what price. They seem to do it so often that not even the version number is enough - you have to look at the lot code too. That suggests A LOT of changes. Why they don't just add another couple of digits to the part number to specify rank and chip manufacturer I don't know. Crucial seem able to do that.

[Percy1983]

There is a performance benefit to 2 ranks per channel, so either 2x 2 rank sticks or 4x 1 rank sticks.

So you will now have 2 ranks in one channel and 4 ranks the other, so who knows.

My setup is 4x16gb sticks and all are 2 rank (bought together) so I have 4 ranks in each channel.

Here is some testing: https://www.igorslab.de/en/performan...yberpunk-2077/

It seems single rank dual channel is a problem and everything else is ok.

[DanceswithUnix]

So you will now have 2 ranks in one channel and 4 ranks the other, so who knows.

Not quite, hence my asking for clarification on which slots the DIMMs went in on the motherboard.

The types are evenly spread, so we get a dual and single rank in each channel, so 3 rank per channel. Not something Igor covered in his testing, but I'm sure it's a common configuration and should perform well in theory at a given transfer clock rate.

OFC DDR5 throws this all out the window, so we are going to have to discover and learn a new set of memory quirks

[Percy1983]

Not quite, hence my asking for clarification on which slots the DIMMs went in on the motherboard.

The types are evenly spread, so we get a dual and single rank in each channel, so 3 rank per channel. Not something Igor covered in his testing, but I'm sure it's a common configuration and should perform well in theory at a given transfer clock rate.

OFC DDR5 throws this all out the window, so we are going to have to discover and learn a new set of memory quirks

Absolutely, but to say to dual and quad rank figures don't deviate to much a triple rank setup is probably fine.

I suppose if there is a certain application which is important you can always test a couple of configs.

[ik9000]

There is a performance benefit to 2 ranks per channel, so either 2x 2 rank sticks or 4x 1 rank sticks.

So you will now have 2 ranks in one channel and 4 ranks the other, so who knows.

My setup is 4x16gb sticks and all are 2 rank (bought together) so I have 4 ranks in each channel.

Here is some testing: https://www.igorslab.de/en/performan...yberpunk-2077/

It seems single rank dual channel is a problem and everything else is ok.

interesting article. There's me with 4x8GB SR Bdie . Ah well nothing i can do about it now.

[DanceswithUnix]

interesting article. There's me with 4x8GB SR Bdie . Ah well nothing i can do about it now.

You can probably clock it higher and tighter than you could with DR dimms, hence overclockers have tended to favour single rank.

[Percy1983]

interesting article. There's me with 4x8GB SR Bdie . Ah well nothing i can do about it now.

4x1R is great it will work great with 2 ranks per channel, you just don't want 2x1R leaving 1 rank per channel

[AGTDenton]

Thanks all

While I'm in no desperate need to change, I did a bit of a window shop as a what if.
The choice of DDR4 in the high end segment will start depleating now, so I'm thinking should I just bite the bullet and get the best I can.

What's clear is all our shops are dominated by Corsair at the high end. Scan don't even bother with any other brand.

If I do go for something I'm wondering, stick with 3600, but go with a CL16. Or go with a 4000Mhz and stay at CL18

[ik9000]

4x1R is great it will work great with 2 ranks per channel, you just don't want 2x1R leaving 1 rank per channel

ah, I'm with you now. Yes, the poor performance is with 2x1R not 4x1R. Phew!!

[ik9000]

You can probably clock it higher and tighter than you could with DR dimms, hence overclockers have tended to favour single rank.

at some point i'll have a tinker. Just got it running at 3600 CL16 stock xmp for now.

[DanceswithUnix]

What's clear is all our shops are dominated by Corsair at the high end. Scan don't even bother with any other brand.

I get the impression that Corsair do some cracking volume discounts, and at one time they had a good reputation so it didn't matter.

I've bought memory directly from the Crucial and Kingston memory shops in the past. It sometimes takes a week for the stuff to turn up, but they are often competitive on price, and you get more detail on what you are buying.

If I do go for something I'm wondering, stick with 3600, but go with a CL16. Or go with a 4000Mhz and stay at CL18

16/3600 = 4.44ns
18/4000 = 4.50ns

So about the same for latency at the ram end. Not sure if the infinity fabric on 5000 series cpus still have a sweet spot for 3600MHz though, I'm sure someone will chime in with that nugget. I'm running 3200 ECC here with a stupidly bad latency, so don't know

[ik9000]

I get the impression that Corsair do some cracking volume discounts, and at one time they had a good reputation so it didn't matter.

I've bought memory directly from the Crucial and Kingston memory shops in the past. It sometimes takes a week for the stuff to turn up, but they are often competitive on price, and you get more detail on what you are buying.



16/3600 = 4.44ns
18/4000 = 4.50ns

So about the same for latency at the ram end. Not sure if the infinity fabric on 5000 series cpus still have a sweet spot for 3600MHz though, I'm sure someone will chime in with that nugget. I'm running 3200 ECC here with a stupidly bad latency, so don't know

isn't the formula CL*2000/MHz? So 8.9ns vs 9ns respectively? That 0.1ns is like FOREVER man. If could add up those 0.1ns over your lifetime it;d be what? Enough time to sneeze and blink, maybe even take a sip of water.

5000 series are supposed to have improved use of the infinity fabric etc but the 3733 1:1 / 3800 2:1 transition to 2:1 decoupling still applies, so 3600 is the common sweetspot for 1:1 given the anecdotal lottery of getting 3733 to run stably.