In my BIOS I have an option for CPU VTT and another for QPI/PCIE PLL. These are not related, correct?
http://www.evga.com/forums/tm.asp?m=100494809&mpage=1&key
CPU VTT Voltage (default: 1.1V (+0mV in BIOS) Intel's max 1.35 (+250mV)
What it does:
VTT connects the cores with the memory. Raising VTT helps keep a system stable at higher QPI rate. Since QPI is calculated from bclk: the higher the bclk the more VTT voltage you will need. VTT is also called "QPI/DRAM Core" on other motherboards,
Prevent CPU damage: VTT voltage must be within 0.5V of VDimm. Vdimm can fluctuate by as much as 0.05V from settings so you may want VTT within 0.45V of VDimm for that extra margin of safety. Example: if Vdimm is 1.65V, then VTT must be at least 1.20V.
When to raise CPU VTT Voltage:
* BSOD 124 "general hardware failure"
* LinX errors happen only after 10 min or more
* LinX hangs but does not BSOD
* LinX reboots without BSOD
You know CPU VTT Voltage is too high when:
* Most users try and stay below 1.45V (+350V) for 24/7 use without additional direct cooling.
* The motherboard doesn't read the temp so you may need an IR thermometer to be sure you are not pushing VTT too far.
QPI PLL VCore (default: 1.1v, <1.4v is pretty safe)
What it does:
Keeps on-chip memory controller in-sync with bclk.
When to raise QPI PLL VCore:
* Try raising this along with Vcore and VTT, but in smaller increments.
* Helps stabilize higher CPU Uncore frequencies and QPI frequencies (in CPU feature)
* Try raising this when you increase memory clock speed via multiplier.
* Try raising when LinX produces errors after a few minutes without BSOD