Undervolting a Laptop

Delph1 writes "Laptops often comes with two Achilles heels, heat and limited battery time. There are, if not cures, at least remedies to make them less obvious. By lowering the voltage to the processor you can not only drastically lower the heat dissipation, but also increase the battery time significantly. NordicHardware gives a nice walk through on the process and was able to boast 18% lower temperature and a 20% reduced power consumption."

Counter productive maybe?

[squoozer]

Surely if you drop the voltage your are going to have to under-clock the processor (reasoning that to over-clock you need to increase the voltage). Most processors for laptops already throttle the processor down when under light load now-a-days which must be a great energy saving. Would under volting it really then save more or would you just end up with a laptop that is dog slow? I'm sure if it was this easy one of the big laptop producers would already be doing it as a 20% increase for basically nothing would give them a fantastic advantage.

Re:Counter productive maybe?

[Anonymous Coward]

There are definite gains to be made, even at the top speed; you just need to experiment. It works quite well because you can specify a voltage for each clock speed (or use the default tables). As long as you don't crash the OS, it won't go any slower than it would have otherwise.

Lots of laptop manufacturers are bundling appropriate software to do this for you these days, too.

18% -- that's really funny

[Jason1729]

How do they come off saying a reduction from 78 to 64 degrees F is an 18% reduction in temperature? The Fehrenheit scale is arbitrary and does not have a meaningful zero point.

In celsius, their reduction is 26 to 18 degrees, a reduction of 31%

Why not define a new scale with the same degrees but 0 degrees (new scales) = 63 degrees F. Now on the new scale they've reduced the temperature from 15 to 1 degree, a reduction of 94%....wow that's way better than their lousy 18%.

Their number is totally meaningless.

Also, "undervolting" is not a word.

Why?

[Eightyford]

Why not just underclock the processor? Adding more ram, dimming the screen, and using a virtual cd drive should also help considerbly.

Re:Counter productive maybe?

[NitsujTPU]

You end up with a laptop that is dog slow. You're right, most modern laptops throttle themselves effectively in order to reduce power consumption.

What the guy is doing, however, is trying to lower the voltage consumption to the line where the processor starts to behave a little flaky, and then pumping it up just a bit over that. Processors are made in big batches, some of them just work better than others. If yours happens to be one of the good ones in the batch, you can reduce the voltage while maintaining performance (not needing to bump down the clock speed).

If you really obsess over it, you go into the research that my roommate does, where he spends endless hours, days, and weeks tweaking processor floor plans and running them through simulators. You might hope to build a more efficient processor through all of this.

I wouldn't recommend doing this if you're not partial to your laptop randomly hanging while you're working on it, but everyone needs a hobby.

Re:Too much misinformation here.

[TheGuano]

Oh, one more thing: undervolting is generally SAFER than overclocking, or overvolting to overclock. Providing less power to the CPU can cause errors or crashes, but it won't fry your CPU like overclocking/overvolting will!

Re:18% -- that's really funny

[jandrese]

Wouldn't it make more sense to compare the percentage drop against room temperature. As in:

Pre: 24 degrees Fahrenheit over room temp
Post: 12 degress Fahrenheit over room temp, a 50% savings!

Obviously no amount of undervolting would ever get the processor to absolute zero, it's going to bottom out at room temperature (when reduced to 0 volts).

Re:18% -- that's really funny

[santiago]

The correct zero point to determine the reduction in heat output would be room temperature. Compare the difference between room temperature and the high-volt processor with the difference between room temperature and the low volt-processor. After all, if it were outputting no heat at all, it would be sitting at room temperature, a 100% reduction in heat output from its initial running state.

Re:Parent is a Bad Idea

[techfury90]

But most CPUs since the late 1980s are CMOS.

Re:No Con's?

[ccool]

Actually, yes there is some Cons... By doing so, you could have stability problems, if you're unlucky... There is a reason why Intel don't do that right out of the box. Transistors need a minimum voltage to work correctly.

Half of slashdot is clueless on this one...

[black hole sun]

No shit? I have an Acer Travelmate 8104 and I have the same control panel you do. All Pentium Ms come with thermal throtlling. The point, dear friends, and what makes this useful, is running the laptop AT FULL SPEED but with a lower voltage. My max speed is 2.0GHz, with a default voltage of 1.308 V. I can safely reduce this to 1.068 V.

I can also take my min speed voltage -- 700MHz -- and reduce it as well, from 0.988 to 0.700 V.

The REASON for doing this is that Intel gives a generous amount of power to their CPUs--enough to make sure ALL (or at least 99%) of their wafers from the factor work correctly. More often than not, you can decrease their "safe" value an appreciable amount to raise battery life and lower thermal output.