Slashdot Mirror
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."
ATI Tray Tools (or a similar program) will let you underclock your video card too. Good for when you have a hulking gaming laptop, but aren't playing games, and don't want to use it as a space heater for your living room.
OR you can just buy a laptop that allows you to do this stuff natively.
,how bright the panel is if wifi is on and stuff like that all through software.
I have an acer aspire 1691 laptop and i can control how fast i want the cpu to run
Why would I undervolt it when my laptop can do it through software already.
This sounds like a really BAD idea to me. Low Voltages can produce the exact opposite of the intended effect. Instead of lowering the power consumption, you'll get higher amperage spikes as the equipment draws more power to compensate. The result is that you could be damaging your electronics and not even know it.
I'll grant that modern manufacturing methods have greatly increased the survivability of hardware under less than ideal conditions. However, that shouldn't be taken to mean that you can't do serious hardware damage by operating outside of the device's specifications.
Javascript + Nintendo DSi = DSiCade
Generally speaking, limiting processor power limits maximum clock rate. If you undervolt you generally underclock. Most mobile processors already have a power-saving scheme that allows you to select the highest speed that will be used while the system is on battery. Even older systems (like my stinkpad A21p with Mobile P3) have multiple speeds and they will run at a slower one automatically when on battery. So there's not much of a difference unless you're reducing voltage to something lower than the system does automatically.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
CHC = Centrino Hardware Control, now called Notebook Hardware Control.
CHC/NHC even has built-in stability testing.
It's fairly easy to run 400MHz FSB Dothan CPUs at 533MHz FSB on Sonoma (i915) or ATI Xpress200 laptops. I run a Pentium-M 715A (1.5GHz) at 2GHz with only 1.14v.
at least my Thinkpad does. The 'access IBM' button explains everything for you or right-clicking on the taskbar battery icon gives you choices of battery saving which does everything mentioned in the article. I am not advertising IBM or anything. Only pointing that out. I am sure other brands have similar functions too.
I don't think many people have a use for this. The processors shut down when they're not doing intensive work, and when they are (playing games, encoding) you more than likely have them plugged in an outlet. I don't know about heat, as I've never had a problem (I have an Athlon XP mobile).
Send email from the afterlife! Write your e-will at Dead Man's Switch.
We already have the kelvin scale where 0 is absolute zero - where all particles in a mass would have no energy. 0 K = -273 C All calculations involving heat and energy should be done using this scale or become invalid And I really doubt that the kelvin scale was used to give the figures quoted in the first post. They seem a bit high and arbitrary.
This procedure was described some months ago here, but without obnoxious "i spread my article over infinite pages in order to get more clicks" practice. I have been undervolting my Dothan a long time, using this little patch and some modifications to vidc. This keeps the fan off most of the time, saves some battery life and has no other impact whatsoever.
It seems a lot of people just assume that undervolting would be something akin to getting the inverse result of overclocking.
Here's the link to an interesting page about undervolting pentium M processors.
Experience shows that the processor may continue working correctly at lower-than-nominal voltages and frequencies, thereby reducing power consumption, heat and fan noise.
Even if your system seems stable, it may still suffer transient faults leading to arbitrary data corruption. In addition, errors in following these instructions (or changes between processor models) may operate the CPU above its nominal parameters, with effects up to and including laptop meltdown.
There's also a thourough discussion and user results from undervoltage on this thread.
Nouvelles de jeux et technologies en français. TC
Undervolting a processor without changing the clock does not affect performance. With a processor, the clock synchronizes the electric pulses which maintains a constant instructions-per-cycle rate. As long as the voltage is high enough to create adequate digital voltage differences, the processor will function properly. You're basically using a letter opener instead of a kitchen knife to open a sealed envelope. Both approaches get the job done, but one's more efficient than the other. And if asked to do so, you could open the same number of letters per hour with either tool.
Also, for the Gentoo users: HOWTO Undervolt a Pentium M CPU.
mnemonic_
The Celsius zero is just as arbitrary as the Fahrenheit zero. The only true "zero" is absolute zero, at -273C or -459F. Using either scale, the "percentage reduction" is around 2.7%, for what it's worth. It shouldn't matter what scale you use when talking about percentages, assuming you use the true zero. If an object becomes 10% lighter, it doesn't matter whether you use pounds or kilograms, does it? Of course, you use percentages even if it doesn't make sense. (78-64)/78 is around "18%", but isn't a very meaningful number. Switching to Celsius doesn't help here, but Kelvin (or Rankine for those Fahrenheit fans) does.
Ohms Law doesn't work like that..
If you lower the voltage, the components will simply stop working as you go below their operational rate.
Put it another way.. as you approach zero volts, does current approach infinity? The answer is no.
There is no performance hit here. The thing with undervolting is trying to find the sweetspot for the processor. I.e. the lowest possible voltage at which the processor works just as it is suppose to. If you are experiencing problems you've gone too far. Some users have managed to go as far as 30% with their Pentium Ms.
No, no cons. Most processors, especially mobile variants, can operate above their "standard" specification. So even if the spec calls for 2GHz @ 1.5v the processor might be able to operate correctly at 2.3GHz @ 1.5v. Similarly, a processor with a spec of 2GHz @ 1.5v could operate at 2GHz @ 1.3v. Thus, no performance hit. This is because after the processors are manufactured they are tested and separated based on the highest performance they can reach under a set of standards set forth by the manufacture. This means that two processors coming off the same wafer could actually become an AMD 64 2800 and an AMD 64 3000 for example. Now, one of those 2800's could have been a 2950 but since AMD doesn't have a 2950 it was put in the 2800 bin. Think of it as a lowest common denominator that ensures even the shittiest processors run fine. ...and it only voids your warranty if you tell them.
Back in 2000, Transmeta started producing chips with Longrun technology, which automatically varied processor frequency and voltage many times a second in response to the current processor load. The technique is quite effective in reducing heat and increasing battery life.
Photo editing, for the most part, is more memory intensive than CPU intensive.
SJW: a person who perceives an injustice, and while correcting it, commits a greater injustice.
TTL is not a current-intensive design. There is some amount of current, but the only reason your CPU draws a significant amount of power (current x voltage) is because there are millions of transistors. The transistors will not draw more current to compensate unless there's a current feedback loop (there isn't, otherwise you wouldn't need, or even be able to have, external voltage controls); they'll simply cease to function properly. There is a feedback loop for the power supply on the motherboard (just a regulator really), but that's what we're manipulating, so overcurrent issues shouldn't exist. More importantly, the regulators on the motherboard should prevent overcurrent conditions.
The designs are trade secrets, so we'll probably never know for sure, but it doesn't even make sense to put any sort of voltage/current regulation on the chip itself since a) real-estate is at a premium b) regulators need to be relatively large, since they handle ALL the current for the CPU and c) they generate a LOT of heat. I haven't looked at laptop motherboards, but on a desktop motherboard, you'll see usually 3-6 transistors mounted vertically screwed to heat sinks near where the power supply connects. Touch them if you want. The heat sinks should be grounded, so the only thing you'll probably hurt is your fingers.
https://www.eff.org/https-everywhere
But wouldn't that significantly reduce the speed of the processor? If so it will take longer to perform the tasks, and that pretty much cancels out the longer battery life... No?
No, you don't sacrifice any performance, You just try to find the lowest possible voltage at which the processor will work just as well as it did before. Processors are simply set to work at a voltage at which all of them work well, but in fact many of them work just fine at lower voltages to.
Some of you talk about Intel Speedstep technology and similar which lowers the frequency and voltage when suitable, that is not the same thing. This should be considered an improvement of that as you try to go even further with even lower voltages. Of course without loosing any performance nor causing any instability.
There are plenty of software that allow to stress-test the processor in order to ensure that the CPU is stable at the voltages that are set, such as prime95, that is mentioned in the article. It does not take "endless hours" to do that either: you just set the voltage you want to use, launch the stress-test utility, go to bed, and check if there are any errors in the morning... Then you can effectively determine the minimum voltage that is required to keep a stable system.
Actually, after having read the article, you do get the savings without a hit in performance.
Here's how I understood what was written:
When the processor is running at a particular clock rate, it is supplied a certain voltage. Reduce this voltage, and the processor clock likewise slows down. This feature is not changed.
What IS changed are the voltage thresholds when this speed shift happens. For example, when the processor was running at the reduced clock speed, the voltage (VID) was 1.000 V. However, the author was able to reduced this voltage down to 0.925 V. Hence, when the processor was set to run at the lower clock rate, the VID was only 0.925 V instead of 1.000 V. He then adjusted the settings so that the clock runs at it's original reduced speed with the new lower voltage.
For the faster clock rate, the VID was 1.450 V. However, he was able to get the processor to run at full speed at 1.175V. Again, the clock speed is the same, but the VID itself is lower. Thus, for each speed state of the processor, he was able to run it at a lower voltage.
The best analogy I can think of is the final drive ratio on a car; you have two gears, low and high, and an engine that normally runs at two speeds, say 1000 and 2000 RPM. You only drive at two speeds, 25MPH (1000 RPM) and 50 MPH (2000 RPM.) You tweak the gear ratio in the transmission and engine speed such that, in the end, the car still drives down the road at 25 or 50 MPH but now the engine turns over at only 850 and 1900 RPM. Low and high road speeds are unchanged, but the engine speeds are lower.
Why don't laptop manufacturers do this? They would have to tune these voltages for each individual processor. I'm no expert in overclocking, but if I understand it right, same-model processors can be overclocked at different rates: If you and I have the exact same model processor, you may be able to overclock it more than I can overclock mine, due to manufacturing tolerances. The same principle seems to apply to undervolting; it has to be done in a controlled fashion on a machine-by-machine basis, over a period of several hours.
Government's idea of a balanced budget: take money from the right pocket to balance...oh who am I kidding?
1.8GHz at 1.340V (default): Idle 40C. Load 58C. (Approx).
1.8Ghz at 1.134V: Idle 39C (there won't be much difference at idle). Load 51C.
600Mhz at 0.980V (default): Idle 35C. Load 41C.
600Mhz at 0.700V: Idle 35C. Load 39C.
I don't remember what the exact difference was in battery life, but I think I got about 30 minutes more out of a 12-cell battery (from 4.5 hours to 5 hours).
If you want to be pedantic...
.25, a 25% difference in temperature change. And that's the important number.
I don't want to be pedantic, but if I did, I'd consider the change in temperature as the important measurement. After all, there's not much chance that the computer will be working at anything near 0K. So, consider the "zero point" to be room temperature, or about 295K.
So, at normal voltage, the peak CPU temperature changed by 56K. With reduced voltage, the peak CPU temperature changed by 42K.
1 - (42K / 56K) =
-h-
It's pretty much all lost to heat. The "work" done by the electricity it to provide a signal where high voltage indicates 1 and no voltage (ground) indicates zero. Every time a transistor switches either from 0 to 1 or from 1 to 0, current travels through it, using power which is released as heat. The higher the clock speed the more transistions, thus the more power consumption. Lower voltage reduces power consumption (power = volts x current(amps)), but as the "high" voltages becomes lower, the transistors much be more precise (it's easyer to tell the difference between 0V and 5V than it is to tell the difference between 0V and 2V). This is why overclockers usually increase the voltage, since at higher than spec frequencies there is more signal degradation which could (and does) make the system less stable.