When switching from 2 DIMMs to 4 DIMMs of memory, what gets stressed more?

[whoopsiesz]

Hi. I've Asus Prime Z370-A and Intel i7-8700K CPU and with the BIOS settings that I've done, everything seems stable at DDR4-3200 with 2x DIMMS which are part of the kit G.Skill F4-3200C14D-32GTZ, placed in Dual-Channel.

However, when I introduce another kit of 2 DIMMs, so it's now 4 DIMMs (each two DIMMs being in dual-channel), the system won't boot to POST for like 2 minutes (memory training?) and then when it does the POST shows a message that says that I should enter BIOS (via F1 key) and change settings because system failed to POST due to system instability and at the same time POST has set RAM speed to 2133Mhz which works just fine with 4x DIMMs, I noticed.

The question is: which parts of the mobo or processor are being required to give more voltage or current(amperes) ? or something else?

For example, does the CPU voltage have to be a bit higher so that its integrated memory controller can more adequately handle the extra DIMMs ?

This might especially affect me because I've set the IA AC/DC Load Line from 1.2 MOhms (aka the 'Auto') to 0.01 MOhms which also required a slight CPU voltage offset increase of +0.05V to be stable and not reboot during prime95 load, but what I like about this, and why I chose to do it, is that the voltage doesn't fluctuate as much compared to idle vs load so it's at about 1.1V (hwmonitor64) with very tiny fluctuations, instead of seeing it go up to 1.3-1.4V for example.

Also, to note, that if I simply Load Optimized Defaults in BIOS, the 4x DIMMs will subsequently work just fine(well, after the 40sec memory training that happens after Save&Exit), without any pre-POST delays during cold boot (it's just 3 seconds tops). But, with my original BIOS settings, to get the DIMMs to not delay pre-POST and work, I'd have to set 1.45V or 1.506V on the DRAM voltage instead of the usual XMP auto-set-by-BIOS voltage of 1.3530V. And as soon as the PC cold booted just once, changing the DRAM voltage back to 1.3530V still keeps the 4x DIMMs working, regardless of how many warm boots I do, with no errors in memtest86, but if I turn off (AND remove power plug so the power is fully drained ie. 1min later, iirc this is needed too), then cold boot is once again going to fail with this 1.3530V voltage (due to my other BIOS changes like the above-mentioned IA AC/DC Loadline settings etc.), unless I once again set it to like 1.5V let's say, then it will cold boot... and I can repeat the above voltagedown and warm reboots and it's all stable, as if something only needed the extra voltage temporarily during cold boot / memory training phase and since warm boots don't do memory training, no issues there.

So clearly something(voltage, amperes?) isn't enough when using 4x DIMMs vs 2x DIMMs, but what I'd like to know is what exactly? is it just the CPU voltage? (maybe it needs more than +0.05V now with 4x DIMMs ?)  it can't really be the DRAM Voltage, because it works with 1.3530V when Load Optimized Defaults are used. Could be something else I've changed too.

Any ideas, appreciated. Really, any

PS:

I admit that it was confusing to read this about i7-8700K:
"Max # of Memory Channels: 2" and its help: "The number of memory channels refers to the bandwidth operation for real world application."
and actually understand that it means I can have two dual-channels, that is one dual-channel made of 2 DIMMs and one more dual-channel made of another 2 DIMMs, to a total of 4 DIMMs, and yet it's still 2 memory channels: the dual-channel being one channel, 2x dual-channels being 2 channels :)) (I could've looked at wikipedia I guess)
I wish they could explain it better in there, as I almost didn't buy another kit, thinking this CPU only supports one dual-channel aka 2 DIMMs.

[Sebastian_M_Intel]

Hello whoopsiesz, 

Thank you for posting on the Intel® communities.   

The Intel® Core™ i7-8700K Processor indeed supports 2 memory channels (for a total of 4 DIMMs), at 2666 MHz. Based on this, your system is not posting since you are setting the RAM speed at 3200 MHz, which is a non-supported speed, as you already know. 

For the voltages required to make your CPU to support 4 DIMMs at 3200 MHz, we do not support overclocking, Intel® offers unlocked CPUs and the option of doing this for enthusiasts how like overclock, monitor, and stress a system, to make the processor go far and beyond its specifications. However. altering clock frequency or voltage may damage or reduce the useful life of the Intel unit and other components, it could also affect the system stability and performance.

For more details about BIOS, voltages changes on your motherboard, you should check with Asus* for guidance, we recommend keeping the system with the default BIOS settings, or at least meeting the specifications.  

Regards, 

Sebastian M  

Intel Customer Support Technician  

[Sebastian_M_Intel]

Hello whoopsiesz,  

Were you able to check the previous post and check our recommendations? Please let me know if you need more assistance or if you have any questions.   

Regards,  

Sebastian M  

Intel Customer Support Technician  

[Sebastian_M_Intel]

Hello whoopsiesz,  

We have not heard back from you, so we will close this inquiry. If you need further assistance or if you have additional questions, please create a new thread and we will gladly assist you.  

Regards,  

Sebastian M  

Intel Customer Support Technician