Question What priority of DDR4 slots is best when mixing different ram sets?

Jul 3, 2023
I’ve been running two sticks of ram for the past year (G.skill Ripjaws V, 8Gb x 2 DDR4 3600 CL 16) And now i’ve added another two sticks of ram to the PC (T.Force Delta, 16Gb x 2 DDR4 3600 CL 18)
Out of convenience, i just bought a different set of ram because I couldn’t find a matching pair of G.Skill CL 16’s.

I know the difference in CAS could be problematic but so far the PC runs smoothly with no issues.
The DDR4 slots are as follows:
Slots 1&3: G.skill 8Gb x2 CL 16
Slots 2&4: T.Force 16Gb x2 CL 18

I dont fully understand how the system prioritizes which set of ram is used first (if that’s even how it works). I dont want to run into issues with mismatched ram, so trying to avoid that, what ram slots are prioritized or what arrangement of ram sticks do you recommend for this situation? (The T.Force would be prioritized)

I know technically I can live with the new 32Gb and ditch the old 16Gb, but i feel like it would be a waste to not use them since i have the ram slots to fill.
The only thing that'd be considered priority is which slots are preferred to be used, but that's more to do with the memory slot topology than any sort of actual priority. But in this case, you have to make sure the kits are installed in the correct slots since the CPU still accesses the RAM modules in pairs. Refer to your motherboard manual to see if there's a requirement to how to populate the RAM slots.

In any case, I'd imagine three outcomes with this:
  • The setup works fine with mismatched latency
  • The setup doesn't boot, but if you match the latency of the faster kit to the slower one, it'll work
  • The setup doesn't boot at all
Latency only affects how quickly the response back to the CPU is, so in theory I don't see why there would be a problem with mismatched latency as long as the RAM modules from the same kit are in the right slots.


Mar 2, 2023
If you carefully check the Primary, Secondary and Tertiary memory timings chosen by the BIOS using HWInfo, CPUID, Aida64, etc., you might find a glorious mishmash of values culled from the two different sets of DIMMs, plus a few compromise values half way in between.

When one set of DIMMs has a significantly faster/slower Tras, I try to fit the slowest DIMMs (highest Tras) into the sockets first checked by the BIOS. Whether this is A2/B2 or A1/B1 I cannot remember. Make a note of all BIOS timings, swap the pairs over and repeat. I've only tried this on DDR3.

People warn against fitting unmatched pairs with the same part number from the same manufacturer. You've gone one step further by mixing manufacturers. It might be an idea to run a few complete passes of MemTest86+ ti check for stability.