Originally Posted by Desolutional
Setting everything except RAM back to stock is a great way to ensure that your RAM overclocking is going to plan. Rarely does a stable core OC affect RAM stability, but in the odd case it does, sticking to stock should help iron out the issues. Anything up to 2800MHz should be doable with XMP, higher than that could depend on the strength of your IMC (Intel uses 2133MHz JEDEC spec unfortunately for us). I run 2400MHz DDR4 sticks which I could easily drop the timings on, but couldn't run 2666MHz 100% Linux stable for the life of me. I was running 8 4GB, Hynix IIRC, sticks. At the end of the day, anything above 2400MHz yields a lower benefit than 2133MHz to 2400MHz, weirdly. Not sure why there's such a bump between 2133MHz and 2400MHz, but there just is. RAM manufacturers love to bin their kits excessively, as it gives them a selling point for the higher spec'd kits. Sure, you may get lucky and get a kit with a nice set of ICs, but usually you can't push reasonable OCs without excessive tuning of secondary and tertiary timings. Pretty much the same thing with the chips themselves, although J batch seemed to have a nicer OCing range on average. Got my eyes set on the Trident Z series which seem to be listed at a decent price.
I'm not having much luck increasing the clock speed, but it's happy to run with tighter timings. It's running the stressapptest at 2400Mhz 14-14-14-35-1T (along with 4.4core/3.3cache on the cpu). That's with the mem related voltages set to "auto" in the bios.
vccsa - 0.984
vdimm(a/b) - 1.222
vdimm(c/d) - 1.209
Channels a/b are always slightly higher than c/d. Even if I enter a manual settings for dram voltage and eventual dram voltage. Since i was able to boot 2 of the 4 dimms at 2600, I thought it must be close to being able to lock them all in. I plugged in 1.25 as a manual setting for dram voltage. Nope. I was able to boot 3 of the 4 dimms like that. I put the cpu at stock and dialed in some settings that i though would at least get me into the bios. Nope, had to use the memOK button to recover from that. Thought I'd bump vccsa, so put the ram back at stock and turned the system agent offset setting from auto to a manual 0.03. I was thinking that would get added to the .984 value. It booted up and ran with a much lower vccsa (0,88?), apparently the default offset is somewhat more then 0.03. Anyway at stock clocks, the much lower vccsa was all that was needed.
That 2400 at much lower voltages all around worked compared to what I was trying for 2600 and 2666 gave me some pause. Is more voltage what it wants or something else?
Maybe I'll try again later, but for now, I'm just going to tighten the timings a bit and call it a day. Maybe i can get it down to cl11 or 12.