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CMX8GX3M2A1600C9 - QPI/Vtt and DRAM voltage differential query


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Hi all


I have a CMX8GX3M2A1600C9 intentionally running at 1333MHz (despite this being 1600MHz kit - I only need 1333MHz at most, and with a 1-2 week ETA on 1333 kits, I got this 1600 at the same price). The timings are tightened up by default with Gigabyte's BIOS option for 'Performance enhance' left on "Turbo", which gives 7-7-7-20-1T. I have manually set the voltage to 1.64V (no 1.65V option). It is running fine and tests fine with my usual trio of prime95,memtest/linpack.


Now if this is running with a stock i7 (socket 1156) Lynnfield processor, which has a QPI/Vtt voltage of 1.1V per the BIOS, would this break the rule about having a less than 0.5V differential between QPI/Vtt & DRAM voltage (if DRAM is 1.65V)?


However, on one of Intel's motherboards, they specifically reference a maximum 1.65V for the DIMMs used on the Intel motherboard. Given there would be many Intel motherboards and Lynnfield processors in use, along with some 1.65V memory kits, it would seem this reported voltage differential rule isn't an issue if Intel's documentation for their own boards states that it supports DIMMS "with a voltage rating of 1.65 V or less".


Would that be a fair assessment?

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  • 4 months later...

Referencing my PC Specs, I wanted to add that I run my Vengeance kit using the X.M.P. profile.


The IMC/VTT/QPI voltage is increased to 1.2V up from ~1.1V when using X.M.P.


The vDIMM has always been at 1.5V whether set to SPD or X.M.P.


So in the case of SPD my differential was actually 400mv (0.4V) and in the case of X.M.P. my differential was decreased to the minimum of 300mv (0.3V).


Does that mean that in order to run 1.5V RAM I need to increase my IMC voltage even when running SPD in order to decrease the differential?


Obviously I don't want to increase my IMC/VTT/QPI at all due to the fact that it will increase my CPU's temperatures; I am willing to do so in the case of running at DDR3 1600Mhz, but for 1333Mhz, is it really necessary?


Thanks for any help/insight you may have.


ozzyau, you asked a very good question, I would really like to know as well.

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  • Corsair Employees
While ozzyau has the same question or same type of question the answer may be different and should really be asked of Intel more then likely it may be the close to the same answer but the Values will more then likely be different.
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