Dram QPI\Dram voltage relation?

Garmin · 21 Sep 2010 at 13:06

I am new to overclocking the core i7 and would like to find out the proper guides to go buy.

What is the correct relationship between Dram bus voltage and QPI\Dram core voltage, while viewing different sites it has been specified as either keeping them to within .25v or .5v of each other. Which is correct and how critical is it?

Is there a relatonship between QPI\Dram and CPU vcore?

For the moment I have a:

Core i7 950
Asus P6X58D-E
Corsair 6GB XMS3 (TR3X6G1600C8)

V Core is at 1.208v
Bus x 166
Multi x 22
CPU @ 3.52ghz

Mem is at its xmp specs @ 800mhz
Dram 1.64v
QPI\Dram 1.25v

ColonelCage · 22 Sep 2010 at 23:50

There isn't a correct relationship between Dram bus voltage and QPI\Dram core voltage if I understand your question?
There is Dram Voltage which is the Voltage your Ram runs on.
There is QPI Voltage which is the voltage of the links between the components(maybe over simplified

)
There is Vcore which is the main voltage your Cpu runs on.
These are the main 3.

If you want to increase your Ram speed to 1600 or beyond you will need to increase QPI Voltage, this is the Link to the Ram. And it needs to be higher the higher you push the Ram because you are asking more data to be transferred over the links than normal, make sense?
Making the Ram go faster means you need a higher Dram Voltage.
Also as you begin to overclock the CPU you are doing the same thing and will need more QPI voltage.
And presumably you know faster CPU needs more Vcore. They are all linked at the end of the day and this is why they are the three most important voltages on an i7.

ColonelCage · 22 Sep 2010 at 23:54

This ".25v or .5v" i have seen this a lot too, and I beleive it was to do with the CPU voltage Vcore and the QPI Voltage. I hear it's true going outside of .5V on Vcore and QPI will not work. However, you won't be going over 1.35V Vcore anytime soon, and you won't be going lower than 1.2V QPI and no higher than 1.34V so this is a non-issue for the moment, yes?

JonJ678 · 23 Sep 2010 at 13:57

Intel place a hard limit on qpi voltage of 1.35V. It is believed that you can ignore this, as long as you keep the qpi voltage within some distance of ram voltage. 0.5V seems to be the consensus, with 0.45V allowing a margin for error.This is intended to avoid damage to the imc.

I've found that qpi and vdimm are not independent as far as stability goes, and significantly increasing either will require you to increase the other. What the ideal ratio between them is, I do not know and suspect to be motherboard dependent.

A simple approach is to leave ram at 1.64 or 1.65V, and only move qpi. Alternatively lower ram to the lowest voltage it requires for stability, and keep it in mind that if neither vcore nor qpi seems to help in the future, it might need a notch on the ram too.

Garmin · 23 Sep 2010 at 22:06

Vcore is actually at 1.225v
CPUID reports it at 1.208v
CPU PLL is at 1.80v
QPI/Dram is at 1.25v
Dram backed of to 1.58v

CPU @3520mhz
Ram @1604 mhz

UCLK 3207
CPU x 22
BCLK 160

I have noticed when the memory was set to X.M.P it was setting
1.65v on Dram and
1.40v on QPI/Dram

.25v difference

mmj_uk · 24 Sep 2010 at 00:51

QPI/DRAM is badly worded on Asus boards as it's the QPI/Uncore voltage, a stock i7 has 1.1V QPI/Uncore (some boards set it 1.2V) and 1.5V for the DRAM so if there is such a rule it will be a difference less than 0.5V, not 0.25V.

Garmin · 24 Sep 2010 at 11:56

mmj_uk said:
QPI/DRAM is badly worded on Asus boards as it's the QPI/Uncore voltage, a stock i7 has 1.1V QPI/Uncore (some boards set it 1.2V) and 1.5V for the DRAM so if there is such a rule it will be a difference less than 0.5V, not 0.25V.

So is 1.1v QPI/Uncore default for all i7's regardless of speed, 920,930,950 etc..

If Dram is increased by .1v does QPI/Uncore also have to be increased by .1v?

ColonelCage · 24 Sep 2010 at 15:32

Well firstly My default is 1.2V on Gigabyte board so I think its board related more than CPU.
Secondly Dram and QPI/Uncore aren't linked so linearly like that.

Also I spent some time on the OCZ website and they were telling everyone to try QPI at 1.4V as it was the safe bet that whatever board/memory combo you had 1.4 would do it and the X.M.P profiles also reflect this. You're gettin there with the overclock anyway I see.

mmj_uk · 24 Sep 2010 at 15:48

Garmin said:
So is 1.1v QPI/Uncore default for all i7's regardless of speed, 920,930,950 etc..

As far as I know yes, Asus don't allow less than 1.2V which I'm guessing may be to prevent people setting 1.66V DRAM when the QPI/Uncore is still 1.1V.

Garmin said:
If Dram is increased by .1v does QPI/Uncore also have to be increased by .1v?

Well when you increase the DRAM to 1.66V it's usually to run the memory at 1600Mhz or more, this means that you need a minimum of 3200Mhz Uncore and you're unlikely to manage that on the stock 1.1V.

I don't know if there's anything in the 0.5V rule but you'd be wise to stick by it.