Question If I Reduce Memory Frequency, Does Latency Automatically Decline?

[jaydub868]

Greetings. I want to build a PC with an Arrow Lake CPU and a Z890 motherboard. This particular motherboard can accommodate DDR5 native memory frequency of 5600MHz and an overclock frequency of 8666MHz. I'm looking at buying one of two G. Skill 16GBx2 dual channel kits: 1) 5600MHz with CAS latency of 28 which is 10.0 nanoseconds, or 2) 7800MHz with CAS latency of 36 which is 9.23 nanoseconds. If I opt for the 7800MHz modules, but decide later to set the frequency at 5600MHz to avoid overclocking, will the motherboard automatically assign lower latency numbers that align more closely with the 5600MHz modules, or would I have to make trial and error manual adjustments to get the latency down? The motherboard is an ASRock Z890 Pro RS WiFi White LGA 1851 ATX. Thanks.

 

[Misgar]

When you change the memory clock frequency, the BIOS checks the SPD chip and selects the appropriate timings. Sometimes the BIOS tweaks a few settings so they might not exactly match the SPD settings.
https://en.wikipedia.org/wiki/Serial_presence_detect

If there are multiple SPD entries for one clock speed, the BIOS will normally select the fastest (tightest) settings. Higher clock speeds give you greater memory bandwidth. Latency is simply the time between actioning a request and the time when the data becomes ready.
https://en.wikipedia.org/wiki/Memory_latency

 

[jaydub868]

Does it seem likely that the SPD entries for latency in the 7800MHz memory module running at 5600MHz would be as quick or quicker than the SPD entries for latency in the 5600MHz module running at 5600MHz?

 

[Unolocogringo]

The latency of the modules is already lower when running at 7800. AND you have MORE bandwidth.
My option for you is to see how low of a cas latency you can achieve at 7800.
Less latency and faster memory. 34/44/44 would be my objective with that kit.
Best of both worlds.
Why buy high binned memory chips to run them at default jedec speeds.
Color me confused?

 

[jaydub868]

I wouldn't probably run 7800 rated modules at 5600. I was just wondering if I did run it at 5600, would CAS latency remain unchanged at 36. It sounds like if I did run it at 5600, the SPD would force a lower latency number in synch with the relaxed frequency.