How to tell if RAM is dual rank when none are listing the R next to the number of sticks?

[Azurael]

When looking on newegg is does not show an R and the specs don't seem to say duel rank single rank or other wise.

[RONOTHAN##]

TL;DR: It's complicated. 

 

It depends on the type of RAM which you need. If you're on DDR5 at this moment in time (this is subject to change), 8GB sticks will be 1Rx16 (effectively half rank), 16 and 24GB sticks will be 1Rx8 (single rank), and 32 and 48GB sticks will be 2Rx8 (dual rank). On DDR5 though, there isn't really a benefit to dual rank in the vast majority of workloads, so unless you need the capacity there's not much point in looking for a dual rank kit over single rank, especially since it tends to reduce the max clock speed significantly (at least on Intel, on AMD it doesn't really seem to matter). Just avoid the 8GB sticks of DDR5, those are noticeably worse. 

 

If you're on DDR4, however, it gets a bit more complicated. 2GB sticks will be 1Rx16 and are very rare; 4GB sticks will be either 1Rx16 or 1Rx8; 8GB sticks could be either 1Rx16, 1Rx8, or 2Rx8; 16GB sticks could be either 1Rx8 or 2Rx8, and 32GB sticks are guaranteed 2Rx8. To differentiate between those though is a little more complicated. Getting a 1Rx16 based kit in a non-OEM kit doesn't really happen (at least on DDR4), so don't worry about that. Telling whether a kit is 1Rx8 or 2Rx8 though is a bit more nuanced. For 8GB DIMMs, unless they're very early in the DDR4 life cycle (pretty much exclusively in 2016) they're going to be 1Rx8. For 16GB DIMMs, you need to take into account when it was made, who made it, and what memory bin it's in. If it's made before ~2018-2019, odds are it'll be dual rank. If it's made after 2020, odds are it's going to be single rank. If it's in a Samsung B die bin like 3200 CL14-14-14 or 4000 CL17-18-18, it's guaranteed to be dual rank. If the kit is made by Kingston, there's likely to be a datasheet available for it that you can find that will confirm whether it's dual rank or single rank. If the kit was made by Corsair, they do seem to have a tendency to keep kits as dual rank, so if you want to play the odds you've got a better chance getting dual rank with a Corsair kit than a G.Skill kit for instance, but unless you're in an aforementioned B die bin neither is guaranteed. Other than those though, the only way to find out is to buy it and see what shows up. 

[Azurael]

1 hour ago, RONOTHAN## said:

TL;DR: It's complicated. 

 

It depends on the type of RAM which you need. If you're on DDR5 at this moment in time (this is subject to change), 8GB sticks will be 1Rx16 (effectively half rank), 16 and 24GB sticks will be 1Rx8 (single rank), and 32 and 48GB sticks will be 2Rx8 (dual rank). On DDR5 though, there isn't really a benefit to dual rank in the vast majority of workloads, so unless you need the capacity there's not much point in looking for a dual rank kit over single rank, especially since it tends to reduce the max clock speed significantly (at least on Intel, on AMD it doesn't really seem to matter). Just avoid the 8GB sticks of DDR5, those are noticeably worse. 

 

If you're on DDR4, however, it gets a bit more complicated. 2GB sticks will be 1Rx16 and are very rare; 4GB sticks will be either 1Rx16 or 1Rx8; 8GB sticks could be either 1Rx16, 1Rx8, or 2Rx8; 16GB sticks could be either 1Rx8 or 2Rx8, and 32GB sticks are guaranteed 2Rx8. To differentiate between those though is a little more complicated. Getting a 1Rx16 based kit in a non-OEM kit doesn't really happen (at least on DDR4), so don't worry about that. Telling whether a kit is 1Rx8 or 2Rx8 though is a bit more nuanced. For 8GB DIMMs, unless they're very early in the DDR4 life cycle (pretty much exclusively in 2016) they're going to be 1Rx8. For 16GB DIMMs, you need to take into account when it was made, who made it, and what memory bin it's in. If it's made before ~2018-2019, odds are it'll be dual rank. If it's made after 2020, odds are it's going to be single rank. If it's in a Samsung B die bin like 3200 CL14-14-14 or 4000 CL17-18-18, it's guaranteed to be dual rank. If the kit is made by Kingston, there's likely to be a datasheet available for it that you can find that will confirm whether it's dual rank or single rank. If the kit was made by Corsair, they do seem to have a tendency to keep kits as dual rank, so if you want to play the odds you've got a better chance getting dual rank with a Corsair kit than a G.Skill kit for instance, but unless you're in an aforementioned B die bin neither is guaranteed. Other than those though, the only way to find out is to buy it and see what shows up. 

I was looking at DDR5 32 (2x16)

[RONOTHAN##]

10 minutes ago, Azurael said:

I was looking at DDR5 32 (2x16)

Yeah, that's single rank, no way it could be dual rank. It doesn't really matter, DDR5 has so many bank groups that there really isn't that much uplift from rank interleaving that you'd get with dual rank, but they are guaranteed single rank. 

[cmndr]

Ronothan hit it on the head at a deeper level than I have knowledge of. 

 

This is my (potentially incorrect) understanding of the matter. 

As hinted at though, it matters MUCH MUCH less for DDR5.

Each DDR4 stick can operate on a 64 bit channel. 
Internally a single 64 bit DDR5 channel is split into two 32 bit channels. 

 

Rank interleaving allows one half of the memory to refresh while the other half of the memory operates. Splitting the channel in half and being able to address one half of the channel enables much of this benefit anyway. 

 

DDR5 as a technology is generally better architected than DDR4. 

I'm still a fan of recycling perfectly fine DDR4 memory (especially if it happens to be dual rank and reasonably high speed/latency) where possible though. Memory performance does NOT matter nearly as much as a lot of enthusiasts make it out to. If the use case is games, then the difference mainly shows up in benchmarks that run at lower resolutions/settings than would actually be used, with one of the fastest video cards out and with one of the fastest CPUs out. With a more typical configuration... the difference drops to a rounding error.