THE VOLTAGES
Caution: The voltage you set is not necessarily the voltage you get. Furthermore the voltage you read is not necessarily accurate either. The Eleet utility (along with any other software monitoring utility) will simply report what the motherboard tells it to report. When measured independently, these readings are close, but not entirely accurate.
VCore (default: 1.28125v, Intel's max 1.375v, VCore over 1.50v on air cooling is risky)
What it does:
Sets max voltage to the CPU cores. (if Vdroop is disabled, it will set the min voltage instead) The i7 doesn't need much voltage at speeds under 3.8ghz. (For example, I can get 3.8ghz on 1.275 vcore) Beyond that the voltage requirements climb sharply.
When to raise VCore:
BSOD 101 "Clock Interrupt not received from Secondary Processor"
LinX produces errors that are very
LinX errors happen within 1 min of LinX
LinX produces BSOD within the first minute
You know VCore is too high when:
CPU cores approach a peak of 85c on full load
It is unknown how higher voltages may impact the life of the CPU
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.
CPU PLL VCore (default: 1.800V, spec range: 1.65V-1.89V)
What it does:
Keeps CPU clock in-sync with bclk.
When to raise CPU PLL VCore:
May help with stability while increasing the bclk or CPU multiplier.(or may make it worse)
May help with stability past 210 bclk if you observe that during runtime the QPI Link (found in E-Leet) bounces too much.
Not a commonly raised. May actually cause instability. Test this variable alone.
You know CPU PLL VCore s too high when:
Its possible you could actually gain stability by lowering this.
DIMM Voltage (default: 1.5V, Intel's max 1.65)
What it does:
Voltage to the RAM. Despite Intel's warnings, you can raise voltage beyond 1.65 as long as it is always within 0.5V of VTT (as described above).
When to raise DIMM Voltage :
High performance/gaming RAM usually requires at least 1.65v to run at spec. Some manage to get it slightly lower.
Stable bclks over 180 often require VDIMM beyond 1.65V. Remember to keep VTT voltage within 0.5V of VDIMM.
You know DIMM Voltage is too high when:
Memory is too hot. [more info on this is needed]
DIMM DQ Vref (default: +0mV)
What it does:
It is the reference voltage for a pseudo-differential transmission line. The DQ signals sent by the memory controller on the i7 should swing between logic-hi and logic-lo voltages centered around VREF. VREF is typically half way between the drain and source voltages on the RAM. Most VREF generator circuits are designed to center between the VDD and VSS voltages on the RAM. There is usually temperature compensation built into the circuitry as well.
When to raise DIMM DQ Vref:
Vref might be adjusted if (after measurement) it was determined not to be properly centered between VDD and VSS of the DIMM. Without a good osciloscope it's difficult to imagine that most users could set VREF correctly. They may be able to set VREF empirically by moving it up or down and checking for POST or BSOD problems.
Further reading:
http://download.micron.com/pdf/technotes/ddr2/TN4723.pdf The document is for DDR2 but differential signaling is a topic that transcends memory models. It has been done for decades in high-end systems and the advantages/drawbacks are well understood.
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
IOH Vcore (default: 1.1V)
What it does:
Sets voltage for on-chip north bridge which connects PCIE2.0, GPU, Memory, and CPU.
When to raise IOH VCore:
Possibly needed if you overclock your north bridge (via bclk and CPU Uncore freq.)
You know IOH VCore is too high when:
Memory errors? (just a guess)
GPU intensive apps like 3dmark vantage crash. (another guess)
IOH/ICH I/O Voltage (default: 1.5V)
What it does:
some sort of on-chip bus voltage. unknown
ICH Vcore (default: 1.05V)
What it does:
South Bridge chip on the motherboard. Connects all motherboard features, cards (not PCIE2.0), and drives to CPU/memory on IOH
When to raise ICH Vcore:
I don't know if raising this can help in overclocking at all. Possibly necessary in order to keep up with an overclocked northbridge?
You know ICH Vcore is too high when:
unknown. I wouldn't overvolt it too much though.
PWM Frequency (default: 800)
What it does:
unknown
When to raise PWM Frequency:
Overclocking beyond 4.2ghz
You know PWM Frequency is too high when:
VREG approaches 85c
VDroop (default: enabled)
What it does:
Safety feature designed by Intel to protect the chip from excessive wear from voltage spikes. Enabling VDroop keeps actual voltage running below the VCore setting in BIOS
What does disabling VDroop do?
Makes VCore setting the minimum value for actual voltage; CPU will run at higher voltages than what you set in BIOS.
Disabling VDroop is the same as enabling Load Line Calibration on other x58 boards.
Why would I want to disable VDroop?
Some overclockers use it because it allows them to get a high overclock while setting lower VCore in BIOS. This is because the running voltage is actually higher than what was set in BIOS. Disabling VDroop keeps actual voltage higher than what is set for VCore in the BIOS. Enabling Vdroop keeps actual voltage lower than VCore.
It might help if you are pushing the bleeding edge.
Diagnosing errors. What to do when...
BSODs
BSOD "IRQL_NOT_LESS_THAN_OR_EQUAL" (I forget)
BSOD 101 "Clock Interrupt not received from Secondary Processor" Try raising VCore
BSOD 124 "general hardware failure" Try raising VTT
LinX Errors
If you get an error you would have x same (correct) results and 1 different (an error):
If the incorrect result differs slightly from the rest (numbers very close, same powers in Residual & Residual (norm)) it is most likely that there's not enough vcore. In this case only a small vcore bump is usually needed to stabilize the system (alternatively, Vtt & GTL tweaking can sometimes fix this too)
If the wrong result differs much from the others (different power or even positive power in Residual or Residual (norm)) it might be 1) insufficient vcore (the error would happen at the very first runs then) or 2) some memory / NB instability (when it worked for say 10 minutes ok and then produced a different result)
More serious LinX errors:
BSOD during testing (at the very first runs) is often caused by too low vcore
System hangs and remains hung it is almost 100% not a CPU but memory or possibly NB issue
System reboots (with no hang prior to reboot and no BSOD) - a CPU issue, but not vcore related (insufficient PLL or Vtt I guess)
System hangs for a short while and then BSODs - once again NB or memory problem (but might be wrong Vtt / GTL setting as well)
System hangs and then just reboots - wrong Vtt (too low or too high) or GTL settings
