Asrock x99 Extreme4: WTH does DRAM Reference Clock do?

In monkeying w/my overclock I came across a tomshardware article that indicated my Corsair Vengeance LPX RAM should be capable of DDR4-3000 operation (which I've never had luck w/previously). I have the slower version of this memory (w/a CAS of 16 instead of 15). Anyway, after struggling w/getting my system to even boot (@ 125MHz and 3000MHz memory freq.), I noticed by DRAM Reference Clock was set to 100 MHz. Once I set DRAM Reference Clock to 133 MHz and selected the 3000Mhz RAM frequency, the system booted all the way into Windows 7. Note the only change I made was to the DRAM Reference Clock.

The only noticeable difference when changing DRAM Reference Clock is that the selectable DRAM frequencies at a given BCLK are different, but at a BCLK of 125 MHz 3000Mhz is selectable at both the 100Mhz DRAM Reference Clock setting as well as the 133MHz DRAM Reference Clock setting.

Not all memory ratios are working. I mentioned about it in other posts ( can't find it now ).
Anyway, if you set reference memory frequency to auto then it should run at only these combinations which are supported.
Stability at 3000 depends from motherboard. In most cases 125bclk/133 ref is letting you set this frequency. On some boards you can use x30 ratio, 100 bclk/ref clock and it will work too.
Simply best is to keep it at auto and board will select right setting. It doesn't affect performance.

Woomack said:

Not all memory ratios are working. I mentioned about it in other posts ( can't find it now ).
Anyway, if you set reference memory frequency to auto then it should run at only these combinations which are supported.
Stability at 3000 depends from motherboard. In most cases 125bclk/133 ref is letting you set this frequency. On some boards you can use x30 ratio, 100 bclk/ref clock and it will work too.
Simply best is to keep it at auto and board will select right setting. It doesn't affect performance.

Click to expand...

The AUTO settings for DDR4 3000 or DDR4 2800 never worked on my Asrock x99 Extreme4.

What's strange is that at a 125 MHz BCLK I can get a 3000 MHz DRAM frequency at either a 100 MHz DRAM reference frequency or a 133 MHz DRAM reference frequency. Usually, at a given BCLK I can never get the exact same DRAM frequencies available. My 'board doesn't have the x30 ratio.

At around 100 MHz BCLK, the DRAM Reference Frequency has to be set to 100MHz or I have stability issues.

Im confused... do you have X99 or X79? Your signature says one thing, your posts another.