How do you calculate how much of a difference dual channel makes over single channel?

[Cyber Akuma]

So I have apparently been understanding how Dual Channel works completely wrong for years now. I know that it means putting each RAM stick in a different channel, so that you get more throughput over two channels together than just congesting one, but I used to think that meant the reason a 3600Mhz kit would show up as 1800 for example was because each one in a channel was running at that speed to add up to 3600. I found out that I was completely wrong about this, and that the reason RAM appears as half it's advertised speed is because due to modern RAM being double-data-rate, it's accessed twice per clock tick on both the rising and falling edge, so that it is running at 1800 but able to run like that twice per tick.

So this made me try to look up what precisely Dual Channel does since I had it all wrong, but I surprisingly couldn't really find proper answers on this. I saw one claim that it doubles your throughput so if you were reading and writing to them at 16GB/s, it would be 32GB/s. I saw others saying it's somewhat of a "10-15% performance increase" but that doesn't really explain much, and I have no idea if neither or even both of these are true.

With how much talk I have seen of being sure to get dual-RAM kits and to put them each in a different channel for Dual Channel, and how you are leaving performance on the table if you don't do that, I would have expected it would not be hard to Google exactly how it's making a difference and how much of a difference it makes.

 

[pitingres]

The performance difference will depend on what you're doing, and I'd guess it's typically in the single digit percentage points for most games. There are a few youtube comparison videos, check out something like "single channel vs dual channel" on youtube.

The more cache-friendly a program is, the less improvement it's likely to show with dual channel memory.

 

[whateverer]

The performance difference will depend on what you're doing, and I'd guess it's typically in the single digit percentage points for most games. There are a few youtube comparison videos, check out something like "single channel vs dual channel" on youtube.

The more cache-friendly a program is, the less improvement it's likely to show with dual channel memory.

On the flip-side, if you're gaming on integrated graphics, dual-channel makes a big difference!

 

[Cyber Akuma]

I see. I have to admit, with how adamant I see it being brought up when a system is using only one stick of RAM instead of two or when someone is using the wrong channels, I thought it would be a lot more straightforward how much of a difference it makes, or at least easier to calculate the difference. Seems like it's mostly "Eh, it depends" for something that people have been so adamant about for many years now and with no good real way to measure it without just benchmarking on a per-app basis.

 

[serpretetsky]

I see. I have to admit, with how adamant I see it being brought up when a system is using only one stick of RAM instead of two or when someone is using the wrong channels, I thought it would be a lot more straightforward how much of a difference it makes...

Probably the main reason people are adamant about it is because without some other reason, why wouldn't you go dual channel (Note there may be some actual reasons, certain memory on sale for example, but otherwise just get dual channel).

 

[dasa]

Large open world games can see a larger CPU performance gain from the doubling of bandwidth that comes from dual channel.
While the likes of counterstrike can mostly fit in a large CPU cache making RAM speed less relevant.

Also since it only affects CPU performance (unless you run out of VRAM) any GPU bottlenecked gameplay will see no change from the increased CPU performance dual channel can bring.

Here is some tests I ran a long time ago and you can see 6700k with slow single channel RAM is slower than 3770k with fast RAM.

https://www.overclock.net/threads/3...-2133c9-ddr4-2133c15-3000c12-4000c17.1611359/

 

[bigddybn]

The short answer is it doubles your effective memory bandwidth. Double is your answer. That's how much of a difference dual channel makes over single channel.

The long and much more relevant answer is it depends on what task you are looking for an improvement in and how much that memory bandwidth benefits that particular task. If the memory bandwidth wasn't a bottleneck to begin with then doubling it isn't going to make much difference. If it was then how much so will be the determining factor. That bandwidth is pretty good to begin with on modern memory so even running single channel mode is often "enough" for most things people use their machines for.

No good reason not to do it unless $$$ is just that tight and 2 smaller can often be found a cheaply or cheaper than a single larger module, especially when in the common desktop capacities.

 

[funkydmunky]

Put two cheap 4GB in my arcade cabinet as that is plenty. I thought I must always have dual channel. What I run on my cabinet does not need dual channel at all and now I want to do a few other things my two RAM slots are filled. If I just bought an 8GB stick (for cheaper then 2x4GB) I could easily and cheaply double my RAM and be happy. Lesson learned.