Posted on 2007-07-21
Last Modified: 2013-11-17
What is your opinion of undervolting as described below?  What is undervolting?  How is it done?

Undervolting nw8240
I just undervolted Pentium M in my nw8240 . It decreases heat emission with no loss in performance. See this tutorial for it:

I used Centrino Hardware Control rather than RMClock, since I found it to be a little nicer program.

The default voltage at 15x multiplier (2.0 GHz) was set to 1.356 V and at 6X (800 MHz) to 0.988 V. The heat level normally was 85 degrees at 15x and 100% CPU load and 50 degrees at 6x idle.

I was able to undervolt 15x to 1.100 V being stable but I chose to run at 1.116 V just to be safe. The heat level decreased to 70 degrees! So the drop was 15 degrees. The casing (thermal zone 2) is a bit cool er now too - dropped from 85 to 75 or so. It still heats and is of course noticeable, but all this for free is a good deal.

I undervolted 6X to 0.700 V and it worked well, but I didn't notice any difference in idle temperature. Well, maybe 1 or 2 degrees.

Well, is undervolting worth the trouble? Maybe. The computer heats a bit less, but actually it doesn't heat so much normally either - at least mine doesn't. But since undervolting is a free upgrade, you can just do it if you have time. Of course, if you don't mind testing stability, you may just pick some numbers (like mine) and let it go and hope that it's stable for your CPU as well. But note that my stable voltage was a few steps higher than that of the original undervolting thread starter, even though we have the same CPUs, so the stability of an individual CPU cannot be guaranteed without testing.

EDIT: 1.116 V wasn't working perfectly, so I'm running at 1.132 V. So far so good.

EDIT 2: Undervolting increases battery life, I could run the DVD test again at some point and see how the laptops performs now.
Question by:BACS2133
    LVL 69

    Accepted Solution

    Undervolting is achieved by running your cpu at a lower voltage than it is rated.  While it won't damage anything, your system may not start because the voltage is too low.  In general, it saves a little bit of power consumption, but Pentium M cpus are typically matched with the Intel 855 chipset to slow down the clock speed when idle (SpeedStep) and this has a much larger effect than undervolting.
    LVL 70

    Assisted Solution

    Modern CPU's and memory are complex electronic systems that have many parameters that control exactly how they operate --> voltage, frequency, multipliers, temperature, etc.      The most stable operation is to run them at their designed settings;  but they will often operate well outside of those settings ==>  that's what overclockers routinely do (you can also underclock).    With any given set of settings, there is a range in which the operation will remain stable.   For example, if you do not change the multiplier, frequency, or thermal characteristics of the heat dissipation device (heatsink/fan, watercooling block, etc.), then voltage is one of those parameters.   Undervolting is simply reducing the voltage to find the lower "edge" of the threshold where the CPU remains stable with the other parameters unchanged ==> the disadvantage of doing so is that you are running close to the threshold where the system will no longer be stable ... if anything else changes you may have an unstable system.

    Overclockers generally pay close attention to more than a single variable ... if they increase the frequency, they tend to use better cooling than the stock heatsinks; increase the core voltage a bit ; etc. ==> trying to keep a balance among all of the parameters.   Most people will not run the systems completely "at the edge" ... i.e. once they find the maximum point where it's stable, they "back off" a bit to keep some leeway for stable performance.   The same concept makes sense if you choose to undervolt.   Note the comment in your question, "... I was able to undervolt 15x to 1.100 V being stable but I chose to run at 1.116 V just to be safe ..." ==>  that's only 6/1000ths of a volt of "margin" ... which later proved to NOT be enough.   If you're going to run a system at lower voltage than specified, it's a good idea to also reduce the multiplier or the clock frequency to keep things stable.   But I agree with Callandor's comment that SpeedStep has a MUCH larger impact than undervolting ... and that is running entirely within the design parameters, so the system will be much more stable.

    Bottom line:  An undervolted system may run a bit cooler ... but it will also be less reliable than one that's run at its designed parameters.
    LVL 91

    Assisted Solution

    and nobody will guarantee it will operate normally, so if your system crashes, the first thing they will say is : you are not operating it in the normal way.
    I would only try it if the heat is a problem, and even then; see above

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