Dual channel, different number of sticks but same capacity?

[Sergei Tachenov]

Sorry if it was asked before, but it's kind of hard to google for this specific question.

 

Will the following configuration work in dual channel mode?

 

A1: empty.

A2: dual-rank 32 GB stick.

B1: single-rank 16 GB stick.

B2: single-rank 16 GB stick.

 

Assuming all other specs match and there's no compatibility problems due to the silicon lottery. My understanding is that it should work perfectly as a single dual-rank stick in a channel is pretty much the same as two single-rank sticks, for all intents and purposes except maybe extreme OC when actual physical topology begins to matter. Am I wrong? Does the actual number of physical sticks matter for dual channel?

 

And a follow-up: will it work if the number of ranks per channel doesn't match, but the capacity per channel is still the same?

[YoungBlade]

In theory, with a modern DDR4 system, that should work. In practice, there are a lot of variables, so it's going to be a case-by-case thing.

 

I've always had great luck with memory, and I currently run 48GB with 8GB+16GB in each channel. No issues. Yet I've seen others on this forum struggle to get a second stick to work when they bought one that was seemingly identical to the first.

 

The ranks are an important consideration, so I would recommend the configuration you suggested to give each channel the same number of ranks, although you may need to fiddle with trying sticks in different slots if it doesn't work immediately. Even then, there's no guarantee.

 

I would recommend just getting 4x16GB sticks or 2x32GB ones, as that is much more likely to be successful.

[themctipers]

it should work in dual channel (as in, there is nothing logical about it not working) but you never know until you try it. some memory controllers/boards will just crap out on you despite it supposed to be working. neither the ranks per channel or capacity per channel should matter

[RMTM]

59 minutes ago, Sergei Tachenov said:

Sorry if it was asked before, but it's kind of hard to google for this specific question.

 

Will the following configuration work in dual channel mode?

 

A1: empty.

A2: dual-rank 32 GB stick.

B1: single-rank 16 GB stick.

B2: single-rank 16 GB stick.

 

Assuming all other specs match and there's no compatibility problems due to the silicon lottery. My understanding is that it should work perfectly as a single dual-rank stick in a channel is pretty much the same as two single-rank sticks, for all intents and purposes except maybe extreme OC when actual physical topology begins to matter. Am I wrong? Does the actual number of physical sticks matter for dual channel?

 

And a follow-up: will it work if the number of ranks per channel doesn't match, but the capacity per channel is still the same?

This might work. Though I am not sure how stable your system will be. And aside from ranks, timings should also be considered for all RAM sticks as well.

 

For in my experience in mixing RAMs of different sizes(GB) with the same timings, dual-rank sticks should be on the first dual channel slots. For dual-rank sticks are slower in cycles compared to those single-ranks. 

 

But in your case, one stick will not have a pair to link with. I am not sure if your motherboard will read all 3 as single channel array.

With RAM parameters set on auto in BIOS, you can try and do a trial and error. You only have 4 slots to mix anyway. I am not sure how to guarantee it though.

[TrigrH]

Ranks do not equal channels, that single stick with have half bandwidth

[YoungBlade]

11 minutes ago, TrigrH said:

Ranks do not equal channels, that single stick with have half bandwidth

I don't think you understood the question. The OP is asking about running 3 sticks - 1 dual-rank 32GB stick in the first channel, and 2 single-rank 16GB sticks in the second channel.

[TrigrH]

23 minutes ago, YoungBlade said:

I don't think you understood the question. The OP is asking about running 3 sticks - 1 dual-rank 32GB stick in the first channel, and 2 single-rank 16GB sticks in the second channel.

I don't think you did.

Quote

as a single dual-rank stick in a channel is pretty much the same as two single-rank sticks, for all intents and purposes

This is what he asked and he is wrong.

[YoungBlade]

1 hour ago, TrigrH said:

I don't think you did.

This is what he asked and he is wrong.

I'm 99% sure he meant 2 single rank sticks in the same channel, which is basically correct.

 

2 hours ago, Sergei Tachenov said:

A1: empty.

A2: dual-rank 32 GB stick.

B1: single-rank 16 GB stick.

B2: single-rank 16 GB stick.

 

[Sergei Tachenov]

2 hours ago, YoungBlade said:

I'm 99% sure he meant 2 single rank sticks in the same channel, which is basically correct.

Yes, that's exactly what I meant: two single-rank sticks in a channel, or one dual-rank stick of the double capacity in the same channel.

 

It's not that I have the sticks, it was just a theoretical question, as I got curious about this after a discussion on Reddit.

 

Does anyone has a credible source that elaborates on this topic? I'd like to understand it better, as there seem to exist different opinions on this. Even some motherboard manuals, ASRock for example, explicitly say that dual channel is not available when three sticks are installed, without going any further into detail.

[YoungBlade]

1 hour ago, Sergei Tachenov said:

Yes, that's exactly what I meant: two single-rank sticks in a channel, or one dual-rank stick of the double capacity in the same channel.

 

It's not that I have the sticks, it was just a theoretical question, as I got curious about this after a discussion on Reddit.

 

Does anyone has a credible source that elaborates on this topic? I'd like to understand it better, as there seem to exist different opinions on this. Even some motherboard manuals, ASRock for example, explicitly say that dual channel is not available when three sticks are installed, without going any further into detail.

@TrigrHDo you have any insight into this?

[TrigrH]

7 hours ago, Sergei Tachenov said:

Yes, that's exactly what I meant: two single-rank sticks in a channel, or one dual-rank stick of the double capacity in the same channel.

 

It's not that I have the sticks, it was just a theoretical question, as I got curious about this after a discussion on Reddit.

 

Does anyone has a credible source that elaborates on this topic? I'd like to understand it better, as there seem to exist different opinions on this. Even some motherboard manuals, ASRock for example, explicitly say that dual channel is not available when three sticks are installed, without going any further into detail.

Stop talking about the rank. Its not the same as having them in dual channel. Rank counts are only comparable when both compared configurations are in the same channel type (single, double etc).

 

If you do this:

 

The typical behavior is the following:

The 16gb sticks will operate in dual channel.

The 32gb stick will operate in single channel.

 

In some cases:

All sticks may operate in single channel.

 

[Sergei Tachenov]

6 hours ago, TrigrH said:

Stop talking about the rank. Its not the same as having them in dual channel. Rank counts are only comparable when both compared configurations are in the same channel type (single, double etc).

I don't think we're on the same page yet. I'm talking about situation where we have dual-rank 32 GB in one channel and dual-rank 32 GB in the other channel, but in different number of sticks: two single-rank sticks in one channel and one dual-rank stick in the other.

 

Change your picture to one of the following:

• 16, 16, nothing, 32;
• nothing, 32, 16, 16.

I am talking about ranks only to highlight that I'm describing a situation with two ranks per each channel.

[TrigrH]

2 hours ago, Sergei Tachenov said:

I don't think we're on the same page yet. I'm talking about situation where we have dual-rank 32 GB in one channel and dual-rank 32 GB in the other channel, but in different number of sticks: two single-rank sticks in one channel and one dual-rank stick in the other.

 

Change your picture to one of the following:

• 16, 16, nothing, 32;
• nothing, 32, 16, 16.

I am talking about ranks only to highlight that I'm describing a situation with two ranks per each channel.

I give up. the number of ranks DOES NOT MATTER, the single stick will run at half speed.

 

Ranks are ranks, they are added no matter what memory config you have.

[Sergei Tachenov]

All right, maybe I shouldn't have mentioned ranks in the first place. It apparently only adds confusion.

 

1 hour ago, TrigrH said:

the single stick will run at half speed.

Care to elaborate? We have 32 GB in one channel (as a single stick), 32 GB in the other channel (2x16 GB sticks). What do you mean by saying the 32 GB stick will run at half speed? Will we have dual channel in this configuration or not? And, most importantly, why?

[TrigrH]

4 minutes ago, Sergei Tachenov said:

All right, maybe I shouldn't have mentioned ranks in the first place. It apparently only adds confusion.

 

Care to elaborate? We have 32 GB in one channel (as a single stick), 32 GB in the other channel (2x16 GB sticks). What do you mean by saying the 32 GB stick will run at half speed? Will we have dual channel in this configuration or not? And, most importantly, why?

If a stick does not have a pair, that stick will run in single channel. 

[Sergei Tachenov]

1 hour ago, TrigrH said:

If a stick does not have a pair, that stick will run in single channel. 

So it's physical sticks that are paired in dual channel configuration? I was under impression that what matters is how RAM chips are logically organized in a channel, not how they physically distributed among sticks. That's why I brought up ranks in the first place, as I had this idea that a single dual rank stick is logically the same as two single rank sticks placed in the same channel.

[TrigrH]

22 minutes ago, Sergei Tachenov said:

So it's physical sticks that are paired in dual channel configuration?

physical sticks that are paired = dual channel configuration.

Quote

I had this idea that a single dual rank stick is logically the same as two single rank sticks placed in the same channel.

For counting ranks yes. for performance no.

 

So a better comparison is:

 

4x 8gb single rank

vs

2x 16gb dual rank

 

Both configurations have dual channel and 4 ranks of memory. They will perform the same.

 

2x 16gb dual rank will overclock better as most motherboards are daisy chain.

 

[YoungBlade]

10 minutes ago, TrigrH said:

physical sticks that are paired = dual channel configuration.

For counting ranks yes. for performance no.

 

So a better comparison is:

 

4x 8gb single rank

vs

2x 16gb dual rank

 

Both configurations have dual channel and 4 ranks of memory. They will perform the same.

 

2x 16gb dual rank will overclock better as most motherboards are daisy chain.

 

But will a 32GB+2x16GB configuration, with the single 32GB stick in slot 2 and the 2x16GB sticks in slot 3 and 4 function in dual-channel mode?

[Sergei Tachenov]

I begin to think that I need some serious reading about how RAM works. Can anyone recommend any decent books or something?

[TrigrH]

9 hours ago, YoungBlade said:

But will a 32GB+2x16GB configuration, with the single 32GB stick in slot 2 and the 2x16GB sticks in slot 3 and 4 function in dual-channel mode?

Half of the 32gb stick will be in dual channel (if it boots)

https://www.intel.com.au/content/www/au/en/support/articles/000005657/boards-and-kits.html#flex

9 hours ago, Sergei Tachenov said:

I begin to think that I need some serious reading about how RAM works. Can anyone recommend any decent books or something?

 

[YoungBlade]

43 minutes ago, TrigrH said:

Half of the 32gb stick will be in dual channel (if it boots)

https://www.intel.com.au/content/www/au/en/support/articles/000005657/boards-and-kits.html#flex

 

Why would it operate in flex mode if the capacity of both channels is identical? I thought that two sticks in the same channel were treated like a single, multi-rank stick from the perspective of the memory controller.

 

The example shown there is the equivalent of a 32GB stick in slot 4 and a 16GB stick in slot 2 without slot 1 or 3 occupied at all.

 

9 hours ago, Sergei Tachenov said:

I begin to think that I need some serious reading about how RAM works. Can anyone recommend any decent books or something?

I found this PDF from CMU that gives a general overview of how computer memory works, although it doesn't deal with your original question. Perhaps it could be a good starting point for further research.

 

https://course.ece.cmu.edu/~ece740/f13/lib/exe/fetch.php?media=seth-740-fall13-module3.5-main-memory-part1.pdf

[TrigrH]

10 hours ago, YoungBlade said:

But will a 32GB+2x16GB configuration, with the single 32GB stick in slot 2 and the 2x16GB sticks in slot 3 and 4 function in dual-channel mode?

10 hours ago, YoungBlade said:

Why would it operate in flex mode if the capacity of both channels is identical?

Its not. the first channel has 16gb the second channel has 48gb.

[YoungBlade]

36 minutes ago, TrigrH said:

Its not. the first channel has 16gb the second channel has 48gb.

I thought for most motherboards slot 1 and 2 are for channel A and slots 3 and 4 are for channel B, hence why they're also called A1, A2, B1, and B2.

 

What if we had 2x16GB sticks in one channel and 1x32GB stick in the other channel?

[TrigrH]

1 hour ago, YoungBlade said:

I thought for most motherboards slot 1 and 2 are for channel A and slots 3 and 4 are for channel B, hence why they're also called A1, A2, B1, and B2.

 

What if we had 2x16GB sticks in one channel and 1x32GB stick in the other channel?

 

On 2/27/2022 at 9:44 AM, TrigrH said:

 

If you do this:

 

The typical behavior is the following:

The 16gb sticks will operate in dual channel.

The 32gb stick will operate in single channel.

 

In some cases:

All sticks may operate in single channel.

 

 

[YoungBlade]

45 minutes ago, TrigrH said:

 

 

If the two 16GB sticks are in the same channel, how do they operate in dual channel mode?

 

Also, that picture is showing the two 16GB sticks in two different channels, so I don't know what you're getting at.