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Voltage Guide for Core i7

post #1 of 29
Thread Starter 
I see so many people asking what voltages do what, and what BIOS settings one should use when overclocking an i7, or when trying to attain stability. In this thread, I'm hoping to answer as many questions as possible when talking about all the potential voltages. This guide won't be explaining how to overclock your i7, plenty of guides for that.



Vcore
The main voltage used when overclocking your core i7 cpu chip. The higher you overclock, the more vcore you will need to attain stability. In general, you will need about 1.2vcore for 3.6ghz, 1.28vcore for 4.0 ghz, and 1.35vcore+ for 4.2ghz and beyond. Intel recommends 1.375 max vcore for the core i7, but with proper cooling the core i7 can go up to 1.55 Vcore.

Vdroop/Load Line Calibration
Extremely important toggle setting that most x58 motherboards offer in Bios. This setting relates directly to your Vcore. By default, Load Line Calibration is OFF, which means Vdroop is Enabled. The purpose of LLC Off/Vdroop Enabled is to keep your CPU safe from voltage spikes. With LLC Off/Vdroop Enabled, expect your actual idle vcore to be slightly lower than your actual bios setting. Also expect Vcore to further drop (droop) during load.

Example: (Assuming the CPU is stable with 1.25 vcore)
LLC off/Vdroop Enabled
Bios Vcore: 1.3
Actual Idle Vcore: 1.28
Actual Load Vcore: 1.25

On the other hand, if you turn on Load Line Calibration (Which equates to Disabling Vdroop) expect your Vcore to behave differently. With LLC ON/Vdroop Disabled, your CPU is less safe from voltage spikes, but during idle your chip will consume less power than load. Also expect your idle vcore to be slightly higher than bios vcore.

Example: (Assuming the CPU is stable with 1.25 vcore)
LLC on/Vdroop Disabled
Bios Vcore: 1.2
Actual Idle Vcore: 1.22
Actual Load Vcore: 1.25

As we can see, setting LLC/Vdroop has a dramatic effect on our Vcore. Our bios Vcore differs .1 volts in each example, but the ending load vcore to maintain stability remains at 1.25.

Intel recommends leaving LLC off/Vdroop Enabled. Many, including myself, decide against this and go with LLC on/Vdroop Disabled. The benefit is having a core i7 that will consume less power while idle, instead of always having a high vcore during both idle and load. You should be safe from voltage spikes as long as your vcore is low enough to start with, and you have a good power supply.





VDimm
This is the voltage going through your Dimm slots (Aka Ram) Intel recommends a maximum of 1.65, but further research has shown that Vdimm can go up to 1.85. Upping Vdimm can increase RAM stability, especially when overclocking ram or tightening RAM timings. It is extremely important to keep vdimm within .5 volts of CPU VTT aka QPI aka Uncore. Failure to do so results in a dead Core i7 Chip.

CPU VTT aka QPI aka Uncore
The voltage that goes through the part of your chip that is not the core. This voltage controls the core i7's memory controller and connects it to the RAM. This is why it is important to keep CPU VTT within .5 volts of Vdimm. If your Vdimm is 1.65 volts in bios, set your CPU VTT to 1.15 or higher to be safe. Intel's maximum recommended CPU VTT is 1.35 volts, hence why many believe the Vdimm maximum is actually 1.85

PLL Voltages
CPU PLL, QPI PLL, try to refrain from going .1 volt overstock on these PLL voltages. Intel states that the max CPU PLL voltage is 1.88. Strangely, many have found that undervolting CPU PLL to 1.4-1.6 can actually help increase stability.

IOH VCORE aka Northbridge
Intel states the max as 1.35, fiddle around with this setting if your FSB (aka Bclock) is set high, or your ram is still unstable.

ICH VCORE aka I/O ports
No need to mess with these settings, it is the voltage that goes through your Input Output ports.

As always, make sure to have a monitoring program reading all of your voltages. In 90% of cases, your actual idle/load voltages will vary from your BIOS voltages, and you will want to adjust for that accordingly. Also keep in mind that no software monitoring program can be 100% accurate.
Feel free to add any further information/corrections, thanks!
Edited by i7bigrig - 9/29/09 at 11:26am
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post #2 of 29
very nice, this should clear some things up with the new guys.
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post #3 of 29
Helpful, but some things need changing such as LLC, uncore volt delta with vdimm and IOH.
     
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post #4 of 29
Thread Starter 
Quote:
Originally Posted by G|F.E.A.D|Killa View Post
very nice, this should clear some things up with the new guys.
Thanks! I hope so too
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post #5 of 29
Thread Starter 
Quote:
Originally Posted by GigaByte View Post
Helpful, but some things need changing such as LLC, uncore volt delta with vdimm and IOH.
Feel free to clarify gigabyte, I'll throw your info in as well The majority of my experience comes from working with an EVGA mobo, so I might have gotten some terms mixed up when translating terminology for other Mobo manufacturers.
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post #6 of 29
Quote:
Originally Posted by i7bigrig View Post
Feel free to add gigabyte, I'll throw your info in as well The majority of my experience comes from working with an EVGA mobo, so I might have gotten some terms mixed up when translating terminology for other Mobo manufacturers.
Well for LLC, being disabled on a unmodded board (no pencil or resister mods) I never seen any setup give idle volts higher than selected in bios. When LLC is disabled the value selected in bios is the max voltage the CPU will ever see from any spikes that may occur for xxx amount of micro or nanoseconds, however its measured. Anandtech has a good article on on LLC and what its really doing, not helping your CPU or VRMs at all. Yes idle with LLC off will be 5W (+/-2W) more but load is usually less, much less in their test system load was 20W lower.

Regarding IOH there is no info in their datasheet on what the typical and absolute max is for X58, strange as it is as every other chipset has that info posted. Since its still 65nm and similar to P45 I assumed the typ max was 1.15v and absolute was 1.21v, but again nothing is there so iam not sure myself.

.50v delta between uncore and RAM is also not being shown anywhere in their i5/i7 related datasheets, all thats shown is uncore and RAM have their own voltage limits, keep both safe and the delta is not necessary. So far all those that ignore the delta using safe volts for uncore and RAM saw no degradation, those that followed the delta using high uncore (1.32v+) and high RAM (1.75v+) came back posting months later that their CPU is dying.

For any voltage guide, when limits are given a source to proof should be given (Intel, AMD, etc) as well, to speculation and concern
     
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post #7 of 29
Quote:
Originally Posted by GigaByte View Post
Well for LLC, being disabled on a unmodded board (no pencil or resister mods) I never seen any setup give idle volts higher than selected in bios. When LLC is disabled the value selected in bios is the max voltage the CPU will ever see from any spikes that may occur for xxx amount of micro or nanoseconds, however its measured. Anandtech has a good article on on LLC and what its really doing, not helping your CPU or VRMs at all. Yes idle with LLC off will be 5W (+/-2W) more but load is usually less, much less in their test system load was 20W lower.

Regarding IOH there is no info in their datasheet on what the typical and absolute max is for X58, strange as it is as every other chipset has that info posted. Since its still 65nm and similar to P45 I assumed the typ max was 1.15v and absolute was 1.21v, but again nothing is there so iam not sure myself.

.50v delta between uncore and RAM is also not being shown anywhere in their i5/i7 related datasheets, all thats shown is uncore and RAM have their own voltage limits, keep both safe and the delta is not necessary. So far all those that ignore the delta using safe volts for uncore and RAM saw no degradation, those that followed the delta using high uncore (1.32v+) and high RAM (1.75v+) came back posting months later that their CPU is dying.

For any voltage guide, when limits are given a source to proof should be given (Intel, AMD, etc) as well, to speculation and concern
It is also important to note that some cooling configurations allow voltages which would cause degradation in systems with lesser cooling ability; some guides list voltages which are inappropriate for, say, air cooling. A nice liquid cooling loop allows vCore and other voltages to be set at levels which would fry an air setup.
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post #8 of 29
1.55 is the maximum rating, don't forget voltage spikes (with and without vdroop control)

Does not mean you should go that high though, 1.47 is the rule of thumb i tell others now, but 1.55 should be fine going 24/7 for 1 year, but don't expect it to pull through for more than 5 years imo.

oh just re-read it, you're wrong.

1.375 is the maximum default voltage (Vcc) you can receive. If it fails to run at stock clocks at that voltage, it probably won't be used, and probably will be discarded and (hopefully) recycled. It isn't the recommended voltage at all.
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post #9 of 29
FYI, increasing ICH volts may be necessary with many hard drives, especially in various RAID configurations. I'd personally just leave this as auto tbh.
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post #10 of 29
Very very useful info; recomended for all i7 users. +rep
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