How to kill (or not kill) a Skylake CPU
Manufacturers typically test out the upper limits of different voltages and their effects on frequencies and CPU life. They will typically try to kill CPUs so that they can set limits for themselves and recommend reasonable voltage ranges.
Steve: What CPU VCore can be used to kill a CPU?
Hicookie: It's very hard to kill the CPU itself, can even boot 1.9v [VCore] on air, and if you stress the CPU, it will just throttle. It probably won't kill the CPU, but will rapidly degrade. But some voltages will kill components all the way.
VCCIO is going to kill the PCI-E controller inside the CPU at around 1.5v+, but the CPU will still work.
VCCPLL is going to kill the iGPU inside the CPU at around 1.7v+, if kill in seconds set 1.8v, but 1.7v will slow kill. You will see screen come out and go, and screen artifacts. Sometimes the screen will come back, and then go out.
Steve: So what other voltages can hurt?
Hicookie: Nothing I found.
Steve: What about killing DRAM? Intel said that running over 1.35v on DDR3 will cause problems, but many manufacturers have said that 1.5-1.65v with DDR3 XMP is okay through their QVL lists.
Hicookie: The CPU can take higher voltages, we didn't see an issue with this. On Haswell, we ran up to 2.4v, on Skylake we usually run Samsung or Hynix, and they will not be very stable with voltage over 1.9v, which seems to be okay, so we don't try higher voltages.
Steve: Do you have other voltage tips for Skylake?
Hicookie: VCCIO does affect the cold bug. On some motherboards, VCCPLL_OC is linked to the DRAM voltage so if you set 1.5v you might not even have a cold bug with the right VCCIO. So you should buy a gaming or OC motherboard to have a separate rail for VCCPLL_OC and vDDQ [like Gaming G1 or SOC Force].
VCCPLL_OC is external PLL voltage for CPU, inside is the VCCPLL and the internal PLL, which is default 0.9v. So, it's very simple; you need to get the external voltage higher than the internal one like the Haswell VRIN needs to be higher than VCore. So, VCCPLL_OC needs to be higher than the VCCPLL, and the internal PLL helps CPU frequency. You can increase the internal PLL in 15mv steps.
Steve: Are these extra voltages only on the Z170X-SOC Force LN2?
Hicookie: No, it's available on all GBT Z170 motherboards for OC.
Steve: So Internal PLL only helps on LN2 or air?
Hicookie: Only on LN2. Intel patched the CPU to include this setting because it was not possible to overclock over 6.3GHz. They patched microcode and added in the internal PLL offset for going over 6.3GHz.
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