Question Dual/Single rank DDR4 and mem channels

[thilanliyan]

I have a set of single rank Corsair LPX DDR4-3200 ram sticks. Work fine at 1.35v at DDR4-3200.

I wanted to add some more ram recently and bought another set of 32GB Corsair LPX DDR4-3200. Of course they turned out to be different.
The original kit is a single rank Samsung die kit, while the newer kit is dual rank Micron die.

My question is, which slots should the ram be in for ideal performance? The manual says with 2 sticks you only use slots A2 and B2.
So in my case now does it make more sense to have the single rank on one channel (A1 and A2) and dual rank on the other channel (B1 and B2)?

As for speed the system refuses to boot properly unless I set the speed to DDR4-2666 with the sticks in A2/B2 (single rank) and A1/B1 (dual rank).

 

[Shmee]

I am not sure it matters which kit is in which position, as long as the DIMMs are placed so they are matched for dual channel with the other DIMM in the same kit. It sounds like you now have 64GB of RAM, which can make higher speeds on Ryzen trickier. My advice would be to be sure your BIOS is up to date, and then manually tweak frequency, voltages, and timings. Do not use XMP in this case. You most likely will need to increase VSOC I suspect, and possibly some secondary voltages.

 

[thilanliyan]

I am not sure it matters which kit is in which position, as long as the DIMMs are placed so they are matched for dual channel with the other DIMM in the same kit. It sounds like you now have 64GB of RAM, which can make higher speeds on Ryzen trickier. My advice would be to be sure your BIOS is up to date, and then manually tweak frequency, voltages, and timings. Do not use XMP in this case. You most likely will need to increase VSOC I suspect, and possibly some secondary voltages.

Thanks for the info. The highlighted seems like you are saying it does matter that the sticks are in (ie.) A1/B1 instead of A1/A2. Is that correct?

Also something like rank interleaving should be left off as well? Or will that still work with the dual rank sticks?

Yeah I think I will have to update the BIOS. Is VSOC the NB/SOC voltage? I have it at 1.05v right now.

I have not kept up with hardware news and only recently upgraded the full PC after 7 yrs, so didn't know about this single/dual rank business!

 

[dlerious]

Thanks for the info. The highlighted seems like you are saying it does matter that the sticks are in (ie.) A1/B1 instead of A1/A2. Is that correct?

The sticks in A1/A2 should match - same for B1/B2. In other words the original 2 sticks should be in one channel (A1/A2 or B1/B2) and the new sticks in the other channel.

 

[thilanliyan]

The sticks in A1/A2 should match - same for B1/B2. In other words the original 2 sticks should be in one channel (A1/A2 or B1/B2) and the new sticks in the other channel.

You are 100% sure about this?
I see conflicting things when Googling.

In my head I'm thinking "if the CPU is in dual channel mode it should be accessing the same type of memory so the same type of sticks should be on different channels. If I have the sticks in the same channel the CPU would be accessing different types of ram from each channel". Does that make any sense? I'm not an electrical eng lol.

Maybe put another way, if say I have 2 sticks of 4GB and 2 sticks of 8GB, would it make more sense to have the 8GB sticks on different channels and 4GB sticks on different channels? (so that at any one time, the CPU can access the 8GB sticks in dual channel mode instead of 8GB and 4GB)