Question Memory Stability, BIOS defaults were Undervolting (am I doing this right?)

Nov 26, 2020

This is an odd one where it seems my BIOS default settings may have been undervolting my RAM. It would be helpful if people could read the below and let me know if I am doing this right.

I have a custom built system. Motherboard is an ASUS X299 Prime Deluxe. BIOS is current (v3201). My system has some DRAM, Corsair Vengeance LPX 32 GB DDR4 3000 MHz C15 XMP 2.0 High Performance Desktop Memory. All the memory slots are used.

I basically like high performance PCs but I like to run my systems at stock. I do not overclock. CPU turbo is disabled, clock speed is standard (CPU 3.3Ghz). In fact, aside from disabling turbo I leave all the Overclock and AI settings on auto. For some time I have had very occasional blue screen crashes. Like, with say a month between. I suspected hardware although they were ambiguous things that could have been drivers. Mostly it was nVidia crashes, but not always.

Recently there were two bluescreens in close succession and I decided to spend some time trying to track it down. I ran Memtest86 overnight, but there were no errors after 3 passes / 8 hours and I had to reboot into windows to do some actual work. I removed, cleaned and reseated the graphics card. I flashed the motherboard BIOS to v3201, updated the chipset drivers to the latest version on the ASUS website, updated the nVidia driver to the latest WHQL version. I then bought HCI Deluxe Memtest and ran HCI Pro Memtest overnight. Two errors. I am a bit dubious about HCI but I also bought a short OCCT license and after running that overnight it confirmed. Both had memory 2 errors in about 8 hours. No CPU errors on OCCT Linpack.

On investigating the memory I obtained the part number and looked up the default safe specifications (SPD), including voltage and timings, as well as the tested-to specifications. This particular memory part number has SPD voltage of 1.2V and tested voltage of 1.35. I examined the BIOS settings, which were all on auto.

There are voltage settings for 2 DRAM channels in the BIOS - Volt CHAB (DRAM AB) and Volt CHCD (DRAM CD). Both have a box to type a setting and a box to the left showing the actual voltage. Both were set to AUTO. The actual voltages were showing as 1.2 and 1.184, respectively. It looked like, for some reason, the voltage for CHCD was slightly undervolted. I changed the settings manually. I set CHCA to 1.2 and CHCD to 1.2. On reboot they both showed the same (1.2 and 1.184). I adjusted the second value to 1.215 and on reboot it changed to 1.2V. Experimentation shows that whatever I type or put in settings, the actual resulting value is adjusted by some multiple of 0.016V.

I ran the OCCT memory test again with CHCD set to 1.215 (yielding actual value of 1.2V). No errors so far after about 2.5-3 hours. However, I decided to graph the voltages and the value for CHCA would dip slightly to ~1.84 every minute or so. So I adjusted that setting manually to 1.205. The resulting voltage in the little box was 1.2V. I then saved the BIOS settings and restarted the OCCT test, still graphing DRAM AB and DRAM CD. Now there are no voltage dips - both lines stay rock steady at 1.2V and no errors so far on OCCT. I will run it for a few more hours, perhaps HCI overnight.

I will run it overnight to be sure but it looks like the BIOS has been slightly under-volting CHCD and occasionally CHAB. It is unclear if this is some attempt at optimisation. The SPD value is 1.2V but it was dipping to 1.184V. Now I have set the voltages manually to fractionally above SPD and the result is a steady 1.2V. No errors so far.

Is this right though? I do not understand why the BIOS would give 1.184V on a setting of 1.2V.

Also, HCI Design Memtest was a little odd. I have the pro version so I can run many threads off one process, but at times errors would fluctuate. At one point, whilst a thread was starting and not responding, errors went to 72 then dropped to zero.

Thoughts on this post welcome please.


Dec 8, 2019
you should probably leave it on AUTO and enable XMP - then your memory should run at the rated 1.35 and 3000MHz, difference in voltage may be the result of having 4 banks of RAM and a bios preset tucked in there