[SOLVED] Xeon 4210, DDR4-2933 CL 21 and true latency

Oct 1, 2020
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So, I bought a Supermicro motherboard (X11DPi-NT) and a Xeon Silver 4210. I was planning to buy a QVL DDR4-2933 RAM but I just realized that the processor only supports DDR4-2400.
From my understanding, the RAM should still work at the lower speed but the CL will remain the same. That would mean that the true latency will be 17.5ns (21/2400*2000) instead of the 14.3ns, right? Is that 22% increased as bad as it sounds for day to day usage (FreeNAS, Proxmox)?

(I'm still searching for a slower memory but they either not as available, more expensive or not in the QVL.)
 

Lutfij

Titan
Moderator
I would advise on picking lower frequency tighter timings rams to get the most out of the platform. I do have a point to share though, usually rams have varying CL times with respect to the frequency and this varies with brands of ram, so if anything, mind sharing the kit you've sourced with regards to the QVL? I'm sure the timings at DDR4-2400MHz are acceptable.

I assume you used this to calculate true latency?
 

Lutfij

Titan
Moderator
I would advise on picking lower frequency tighter timings rams to get the most out of the platform. I do have a point to share though, usually rams have varying CL times with respect to the frequency and this varies with brands of ram, so if anything, mind sharing the kit you've sourced with regards to the QVL? I'm sure the timings at DDR4-2400MHz are acceptable.

I assume you used this to calculate true latency?
 
Oct 1, 2020
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Thanks for the reply, I didn't know that the CL could vary.
The RAM is MTA36ASF4G72PZ-2G9E2 (QVL). I'm reviewing the data sheet and, if I'm understanding the table correctly, when running at 2400Mhz this module has a CL of 17/18, that's great.

The formula for true latency I got it from here and here is a calculator that gives the same results.
 

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