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FCLK and MCLK BIOS Settings and Readout Confusion

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Kawzman

Member
Joined
Sep 26, 2003
Location
San Diego, CA
In the BIOS, I’m using XMP 2.0 profile 1 which is DDR4-3600 16-19-19-39 1.35V. If I leave the infinity fabric freq setting at auto, CPU-Z reports my NB freq at 899.8 MHz and DRAM freq at 1799.6 MHz. The BIOS description for the FLCK is that when set to auto FLCK will equal MCLK. So shouldn’t the reported NB freq also be 1799.6 MHz? At 899.9 MHz, that’s a 1:2 ratio and not 1:1. I temporarily manually changing the FCLK to 1800 MHz and there were no apparent issues after doing so. Thoughts? Thanks for the support as always!

AMD Ryzen 9 3900X (OC set to auto)
G.SKILL Trident Z Neo 32GB F4-3600C16D-32GTZNC (2x16GB dual channel)
ASRock X570 Taichi
 
DDR = DOUBLE Data Rate. 900 = 1800 MHz.

Please post a screenshot of CPUz showing the memory tab and the SPD tab that displays details about the memory stick.
 
DDR = DOUBLE Data Rate. 900 = 1800 MHz.

Please post a screenshot of CPUz showing the memory tab and the SPD tab that displays details about the memory stick.

RAM Settings.PNG

Yep, I get DDR. I was expecting 1800 = 3600 (like the reported DRAM freq). Not 900 = 1800.
 
Put a load on your cpu and the NB clocks will go up.
IMG_2772.jpg

But isn't that NB Freq setting static? I'm confused. I put the CPU under 100% load and it didn't change, which supports that it's static. I closed and reopened CPU-Z to see if that would force a refresh to a different value while the CPU was under load, no change.

I have the option in the BIOS to specify a value for the infinity fabric freq and dividers (see attached image). So, shouldn't I change the BIOS setting from auto and set it to a specific value? And shouldn't that value be 1800MHz and not 900MHz because DDR = DOUBLE Data Rate and 1800 = 3600 MHz?
 
Sorry... was thinking Intel (that value varies) for some odd reason.

I dont know why the board did that... but make sure you're on the latest bios. Setting it manual won't hurt.
 
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