Is a single stick better with AM5 / Ryzen 7?

[ElT]

When reading through Anandtech's review of Ryzen 7 I came across this:

AMD Zen 4 Ryzen 9 7950X and Ryzen 5 7600X Review: Retaking The High-End

www.anandtech.com

As for memory speeds and capacities supported, while AM5 enforces the use of DDR5, ultimately it’s the individual memory controllers that determine the rest. For AMD’s Ryzen 7000 desktop processors, which are based on the Zen 4 Raphael design, these chips offer support for official (JEDEC) speeds at up to DDR5-5200 for a 1 DIMM Per Channel (DPC) configuration. But, like all other DDR5 products we’ve seen thus far, 2 DPC comes with a significant penalty; in that case the maximum JEDEC speed is reduced to just DDR5-3600.

So as was the case with Intel’s Alder Lake platform, system builders are going to need to put a lot more thought into how they go about adding memory, and how they’re going to handle future memory expansion, if at all. While Ryzen 7000 can drive a 2 DPC/4 DIMM setup, you’re going to lose 31% of your memory bandwidth if you go that route. So for peak performance, it’ll be best to treat Ryzen 7000 as a 1 DPC platform

Not being wise in the ways of memory this completely caught me off-guard. I had imagined Ryzen 7 had some dual-channel set up and I could put in two sticks or four sticks and happy days.

I'm not gaming. It's compiling software and other CPU intensive tasks. And just general system responsiveness. So, am I actually better off just having a single stick rather than multiple of I can get the amount of RAM I need on one chip? I was considering 64GB if I make the jump to Ryzen 7.

 

[Rroff]

It isn't clear from the article but I'm gonna assume you lose ~31% of your peak 1 DPC bandwidth but gain more than 31% going to 2 channel - just don't get as much performance uplift from 1 channel to 2 channel as you do with other platforms - but I might be wrong on that.

 

[Tetras]

I think you may be misreading what they said, DPC means 1 DIMM Per Channel, so they mean two sticks and that 2 sticks per channel (4, in other words) is problematic (and AMD only rate it at much lower speeds), but we already saw that with 12th gen so is nothing new.

 

[ElT]

It isn't clear from the article but I'm gonna assume you lose ~31% of your peak 1 DPC bandwidth but gain more than 31% going to 2 DPC - just don't get as much performance uplift from 1 channel to 2 channel as you do with other platforms - but I might be wrong on that.

Ahhhhh, that would make more sense. But does this mean you're still facing a drop off if you go beyond two sticks?

I think you may be misreading what they said, DPC means 1 DIMM Per Channel, so they mean two sticks and that 2 sticks per channel (4, in other words) is problematic (and AMD only rate it at much lower speeds), but we already saw that with 12th gen so is nothing new.

It is entirely likely I'm misreading it. Though I think it is a little confusing. So that kind of confirms what I wrote in response to Rroffs, post? It's either full clock speed with 1-2 sticks but if you go with 4 sticks you have to lower the speed? Well, unless you can overclock to make up the difference. Does that sound right?

 

[Rroff]

I think you may be misreading what they said, DPC means 1 DIMM Per Channel, so they mean two sticks and that 2 sticks per channel (4, in other words) is problematic (and AMD only rate it at much lower speeds), but we already saw that with 12th gen so is nothing new.

I managed to mix it up a bit there - but yeah. The article doesn't really put it very clearly - would have been better if they supported it with benchmarks of the different configurations.

 

[Tetras]

It is entirely likely I'm misreading it. Though I think it is a little confusing. So that kind of confirms what I wrote in response to Rroffs, post? It's either full clock speed with 1-2 sticks but if you go with 4 sticks you have to lower the speed? Well, unless you can overclock to make up the difference. Does that sound right?

Correct, but it has been the same with DDR4 (and now DDR5) since release. I think anandtech mention it, just because AMD rate the memory controller for much lower speeds than in the 1 DPC configuration. Buying DDR5 and only getting 3600 would be ridiculous.