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Undervolting a Laptop 262

Posted by ScuttleMonkey
from the too-late-for-my-laptop-graveyard dept.
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."
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Undervolting a Laptop

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  • Underclocking (Score:5, Informative)

    by selfabuse (681350) on Monday January 23, 2006 @05:31PM (#14543201)
    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.
    • What for? (Score:3, Informative)

      by Poromenos1 (830658)
      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).
      • Re:What for? (Score:3, Interesting)

        He's talking about the videocard in this particular case.

        But anyways, you do bring up an interesting point. usual power saving features do things like lower the clock rate when not in use, but lowering the maximum clockrate you would lower the speed of the computer, thus the max power it puts out. Knowing that you will be running the processor at max speed longer, you may or may not gain power/heat savings overall for long complex tasks, but I imagine for simple tasks you would.

        now - I don't believe you nee
      • Pre-Centrino P3's underclock automatically as well. My piece of crap Presario 1750 drops the CPU speed from 733 to 600-mumble when external power is removed. This feature extends my battery life from about 1 minute to nearly two minutes. (Compaq's battery charging logic in these Presarios was bogus and their batteries were all defective or ruined by the bugs in the charging logic.)
    • Re:Underclocking (Score:3, Informative)

      by mjh49746 (807327)
      ClockGen can also be used to undervolt/underclock supported motherboards in desktop systems, too. I routinely use it to save power and lower my temperatures when I'm not doing anything CPU intensive, like Folding@Home.

      http://www.cpuid.com/clockgen.php [cpuid.com]

      "They are not in Baghdad. They are not in control of any airport. I tell you this. It is all a lie. They lie. It is a hollywood movie. You do not believe them."

      • All you do is drop voltage to 0. Once you've done this, you'll see a drastic increase in battery life, and virtually no heat output.

        The downside is that it takes like forever to load Word...

    • Rovclock (Score:5, Interesting)

      by wiresquire (457486) on Monday January 23, 2006 @08:27PM (#14544776) Journal
      For you Linux-ers who have ATI cards with no PowerPlay (it's disabled in my video BIOS - bastards!!), I'd recommend checking out rovclock [gentoo.org].

      While it doesn't actually reduce voltage, it can be used to underclock GPU and memory speed. My somewhat unscientific testing has shown no major differences between fglrx and radeon + rovclock with 2D, but I did note a 27% decrease in battery draw for 3D using the fglrx driver.

      Of course, you're trading performance for battery life, and why you'd want to eg, play a 3D game on battery I wouldn't really understand

      YMMV
      ws
  • by squoozer (730327) on Monday January 23, 2006 @05:33PM (#14543230)

    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.

    • by NitsujTPU (19263) on Monday January 23, 2006 @05:44PM (#14543353)
      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.
      • by evalf (931500) on Monday January 23, 2006 @06:56PM (#14543983)
        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.
        • However, this only shows that the CPU is now stable enough to run 8 hours without a noticable error. You might still end up with noticable CPU errors over longer periods of time. I'm accustomed to uptimes measured in months, which I won't get with even slight increases in the CPU error rate.

          That doesn't mean you shouldn't try this, or that you shouldn't overclock (which is subject to similar problems), but you should be aware of the effects and be willing to accept them.

          Manufactorurs don't push chips this w
    • Would under volting it really then save more or would you just end up with a laptop that is dog slow?

      You might be removing the ability of the system to manage its own power. This was the case with my desktop. Dropping the CPU frequency on my P4 based desktop actually made it consume more electricity. At its factory speeds, the system uses abotu 90W when not doing a whole lot, and about 215W when under heavy load. Dropping the CPU frequency to 300MHz caused it to idle at about 110W usage. I did not
    • I underclock and undervolt my laptop using the RightMark CPU utility.

      Speedstep can only throttle my processor down to 600MHz (from a max of 1.2GHz) but underclocking reduces it to an effective 300MHz.

      I do not notice the performance hit, and I do a lot of photo editing on this machine.

      --Pat
    • by frdmfghtr (603968) on Monday January 23, 2006 @07:04PM (#14544060)
      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.
    • That is not what the article is proposing. But even if you underpower your processor so much that you need to underclock it, you still save power. Power consuption increases with the square of the voltage, while speed increases linearly.

  • Computer Performance (Score:4, Interesting)

    by ranton (36917) on Monday January 23, 2006 @05:34PM (#14543243)
    How does reducing the Voltage in this way effect performance? If performance drops, then you could have just bought a computer with less processing power that also had lower power needs in the first place.

    If there are no performance problems, then why dont all laptop manufacturers already do this?

    --
    • by drinkypoo (153816) <martin.espinoza@gmail.com> on Monday January 23, 2006 @05:38PM (#14543287) Homepage Journal
      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.
    • "How does reducing the Voltage in this way effect performance? If performance drops, then you could have just bought a computer with less processing power that also had lower power needs in the first place.

      If there are no performance problems, then why dont all laptop manufacturers already do this?"

      As was stated above: Two reasons. That is:

      a) Mass production
      All processors are different, and some inherently work better than others. The default voltage setting for a laptop should probably be a little over the
  • No Con's? (Score:4, Interesting)

    by randomErr (172078) <ervin@kosch.gmail@com> on Monday January 23, 2006 @05:35PM (#14543248) Homepage Journal
    I just scanned through the article and saw they never listed any con's. How much of a performance hit are you taking? Is there any long term damage on the processor or memory? Are you voiding your warranty?
    • Re:No Con's? (Score:2, Informative)

      by obious (945774)
      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. Th
    • Since he kept the clock speeds (the multipliers) the same as the origianl settings, there would be no perfomrance hit at all. You could introduce your own P-States (faster or slower, anything that the multipliers allow for) if you found a need. For instance if you found watching DVDs would load the CPU enough to move out of the lowest power state, but not really stress the CPU in the high power state adding a mid power (say 6x multiplier) may be a happy middle ground in terms of performance and power cons
    • Re:No Con's? (Score:2, Insightful)

      by ccool (628215)
      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.
  • by ulysses38 (309331) on Monday January 23, 2006 @05:36PM (#14543258)
    i'm not so sure about the heat, but it seems that it would follow.

    "Mobile Intel® Pentium® III processors with Intel SpeedStep® technology let you customize high performance computing on your mobile PC. When the notebook computer is connected to the AC outlet, the new mobile PC runs the most complex business and Internet applications with speed virtually identical to a desktop system. When powered by a battery, the processor drops to a lower frequency (by changing the bus ratios) and voltage, conserving battery life while maintaining a high level of performance. Manual override lets you boost the frequency back to the high frequency when on battery, allowing you to customize performance.?
  • lol (Score:3, Informative)

    by Anonymous Coward on Monday January 23, 2006 @05:38PM (#14543276)
    OR you can just buy a laptop that allows you to do this stuff natively.

    I have an acer aspire 1691 laptop and i can control how fast i want the cpu to run ,how bright the panel is if wifi is on and stuff like that all through software.

    Why would I undervolt it when my laptop can do it through software already.
  • Bad Idea (Score:2, Informative)

    by AKAImBatman (238306)
    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 seriou
    • Parent is a Bad Idea (Score:3, Interesting)

      by Anonymous Coward
      Whee... I mean, CMOS logic will never "try to compensate". There is no feedback. In a typical digital system, only switching power supplies will draw more current when their *input* voltage drops. However, Vcore is the *output* voltage of those, not input.
    • Not necessarily true in open loop systems. Amperage draw is heavily influenced by the voltage applied to the device. Though there are other factors involved (aka clock speed), a lower input voltage will almost always result in a lower amperage draw, which results in lower power consumption.

      I've never seen a light bulb stay the same brightness when I reduced the voltage to it. It gets dim, draws less amperage, and less power.

      Ohms Law [wikipedia.org] regulates this, though in AC environments it isn't as cut and dry as
    • Re:Bad Idea (Score:5, Informative)

      by serbanp (139486) on Monday January 23, 2006 @06:09PM (#14543608)
      Instead of lowering the power consumption, you'll get higher amperage spikes as the equipment draws more power to compensate.

      Sorry, this is wrong in the context of a CPU power supply.

      When you lower the core voltage, several things happen at once:

      1) the power dissipation due to the clock switching is lowered with the square of the voltage reduction. i.e. a reduction from 1.3V down to 1.1V will reduce this power component by 40%

      2) the power dissipation due to the junction leakage and off-state punchthrough decreases by the ratio of the voltage.

      3) but the switching speed of the MOSFET transistors decreases. Effects 1 and 2 are good as they mean an overall lower power dissipation. For 90nm processes and up, effect #1 dominates. For 65nm and below, the effect #2 becomes increasingly larger.

      The downside is #3. Lowering the voltage means that some critical paths inside the CPU logic could become longer than the clock period, generating timing violations and system crashes. The only remedy against this is under-clocking.

      In the end, the one thing you can gain by under-volting is the margin between your particular CPU and the lousiest one in the same class that will still perform OK at the same clock speed. As each CPU is tested and binned especially for power dissipation AND maximum clock speed, this margin is low and the gains minimal. And you spend a lot of time to find out what is the lowest safe voltage.

      If you want less power dissipation and longer battery life, under-voltage and under-clock. This is done automatically already in the mobile CPUs, both from Intel and from AMD.

      • Re:Bad Idea (Score:2, Informative)

        by serbanp (139486)
        Ooops, got carried away and did not really refute the dumb claims the OP made. Yes, the CPU is a monotonic load (i.e. when the voltage decreases, the current decreases).

        The OP may have had in mind some constant-power type of load, where the current consumption is (indirectly) driven so that the output power stays the same. From the I-V perspective, the CPU is a glorified non-linear resistor.
        • Hmm, I think I understand what you (and others) are saying. Basically, the power draw is controlled entirely by the power supply, thus there is no concern over the chip drawing too much amperage. Changing the voltage thus changes the overall power available, resulting in a lower rate at which the chip's capacitors charge. If the capacitors charge too slowly, it could potentially result in a cycle that is longer than the clock rate. This is bad because the state of the chip won't finish propogating before t
      • Re:Bad Idea (Score:3, Interesting)

        by F00F (252082)
        As each CPU is tested and binned especially for power dissipation AND maximum clock speed, this margin is low and the gains minimal. And you spend a lot of time to find out what is the lowest safe voltage.

        It should probably be mentioned here that the "lowest safe voltage" (if there can be said to be such a thing) is temperature-dependent (a function of the effectiveness of a fan, the density of the air, the load on the regulators, the number of components powered up vs. down...), and can even be data-depend
    • I'd like to add that Intel undervolts their Pentium-M cpus to lower power usage already. It also lowers the speed itself of the cpu.

      So given that my cpu on batteries probably switches at least once a minute and is not dead... yeah I think you get the point.
  • by Anonymous Coward
    CHC = Centrino Hardware Control, now called Notebook Hardware Control [pbus-167.com].

    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.
  • by method77 (943066) on Monday January 23, 2006 @05:39PM (#14543303) Homepage
    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.
  • This writeup is great. I just bought a cheapo laptop (Turion ML-32) and other than increasing RAM to 1GB and getting a faster (and cooler/more efficient) 5400RPM laptop HD, I think that reducing power output is one of the most important things for usability.

    Other than just battery life, a reduced heat profile will move the laptop from a desktop replacement to a more usable all-around better box. Will still pale in comparison to my wife's powerbook, but hey, this was half the price and I still can't use OS

  • by Marxist Hacker 42 (638312) * <seebert42@gmail.com> on Monday January 23, 2006 @05:42PM (#14543337) Homepage Journal
    That the CPU can run at a lower voltage- or that voltage of the CPU on a modern motherboard is SOFTWARE Selectable.
    • That the CPU can run at a lower voltage-

      Not surprising at all. It's a mainstay of the processor industry. Since the start of the PC, processor voltage has been decreasing every generation. Generally, the only difference between AMD's "desktop" CPU and their "mobile" CPUs is the stringency of the testing. A mobile CPU that can't handle extreme underclocking/overclocking gets labled as a desktop chip.

      or that voltage of the CPU on a modern motherboard is SOFTWARE Selectable.

      Everything you can set in the BI

  • by Jason1729 (561790) on Monday January 23, 2006 @05:42PM (#14543339)
    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.
    • 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.
    • 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
    • I didn't know that temperature needed a "meaningful zero point" to be useful? How do you determine a "meaningful zero point" anyway. As long as long as you state the scale used what's the problem?
      • You can use temperatures without a zero point, and compare them, and talk about differences between two temperatures. 10 degrees is colder than 15 degrees, and the difference between 10 and 15 degrees is the same as the difference between 15 and 20 degrees. What you can't do is talk about 'twice as hot' or 'twice as cold' or anything involving multiplication.

        It's a common mistake though. I spotted a weather forecast saying that one city would be 20 degrees Celsius today, 'twice as hot' as another city wh
    • by santiago (42242) on Monday January 23, 2006 @06:16PM (#14543673) Homepage
      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.
    • I agree with you, but here's one thought : take the temperature at which your machine quits working (overheats) as a baseline - if they have increased the distance from that temperature (downward) by a certain thermal range - that delta would be the same measured in any current normal scale (Celcius, Farenheit, Kelvin.)

      I'm guessing, but something tells me that 18% isn't going to be that delta.
    • If you want to be pedantic, the percent reduction in temperature was:

      25.6C = 298.8 K
      17.8C = 291.0 K

      (291.0 K / 298.8 K) = 0.974

      That makes it a drop of about 2.6%, not 14% or 31%. Doesn't sound nearly as impressive, but it is more accurate.
      • If you want to be pedantic...

        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) = .25, a 25% difference in temperature change. And that's the impor
    • Well, I suppose undervolting is revolting...
    • Mod parent overrated.

      That's not insightful. Their knowledge of math is sketchy at best.
    • Also, "undervolting" is not a word.

      But "revolting" and "revolted" are. We revolted the CPU to 1.05 Volts.

    • What gets me here is how many people can't figure out that what is being measured is the difference of change of underpowered against the normal (standard voltage). Which of course it is very close but slightly less than the difference in power consumption, all of the power stored in the battery is eventually converted into heat (thermodynamic energy) the slightly smaller efficiency is due imperfect measurement and containment. It doesn't matter what the scale or starting point is as long as the scale i
    • by Odin's Raven (145278) on Monday January 23, 2006 @09:32PM (#14545226)
      Also, "undervolting" is not a word.

      I'm sorry, but "undervolting" is a perfectly cromulent word. I'd agree that percentage was a poor choice for expressing temperature differences, but the primary point remains - undervolting can embiggen battery life.

  • Why? (Score:3, Insightful)

    by Eightyford (893696) on Monday January 23, 2006 @05:43PM (#14543351) Homepage
    Why not just underclock the processor? Adding more ram, dimming the screen, and using a virtual cd drive should also help considerbly.
  • by digitaldc (879047) on Monday January 23, 2006 @05:45PM (#14543371)
    Laptops often comes with two Achilles heels, heat and limited battery time.

    You know, I just found about this and I have modded my Laptop to the EXTREME!
    I just went on a website and then tinkered with my new Dual-Heel Processor.
    It's so EXTREME the battery catches fire 10 seconds after it finishes booting up.
  • by TheGuano (851573) on Monday January 23, 2006 @05:47PM (#14543388)
    Some facts:

    Undervolting is NOT underclocking. You run the same clock speed, you just provide the CPU with less juice.

    You do NOT need to underclock to undervolt, though if you're trying to hit a super-low voltage, a lower clockspeed will let you do it.

    It can be perfectly safe. If you undervolt, and successfully run a Prime95 torture test for 24 hours, you're pretty much set. I'm currently running a 1.8Ghz Dothan Thinkpad at 1.134V (default at 1.8 is 1.340), and 0.700v at 600Mhz (default is 0.980 volts). That's on par or lower than those 1.0Ghz ULV Pentium-Ms!

    • 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!
  • Lowering the voltage REDUCES current flow through the chip, reducing power consumption and heat output. The downside is, you can only lower the voltage to a certain limit before it goes below the threshold switching value for the transistors and the processor stops working. This causes no permanent damage, and is totally reversible by raising the voltage again. The lower the clock speed, the lower the voltage can be pushed. It is common practice among overclockers to try and push the voltage as low as possi
    • But undervolting (Not a word people, it's 'under-powering,' as you're reducing the power if you reduce either voltage or amperage.) can cause some serious problems. I've severely damaged digital cameras and wireless headphones by using lower-powered batteries. (1.2v as opposed to 1.5v) Why could this not happen to a processor, hrm?
  • by Anonymous Coward on Monday January 23, 2006 @05:48PM (#14543396)
    I find that if you disconnect the battery entirely, you end with 0 voltage draw on the battery. 0 amps are drawn, too. You can then go for many days without having to recharge the battery! This greatly increases overall battery life as well because of less wear and tear. With my Windows desktop environment being riddled with spyware and viruses, my productivity is only reduced slightly when I do this.
  • by Razlor (846966) on Monday January 23, 2006 @05:50PM (#14543416)
    This procedure was described some months ago here [notebookforums.com], 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 [localhost.ruhr.de] 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.
  • by Destoo (530123) <<destoo> <at> <gmail.com>> on Monday January 23, 2006 @05:52PM (#14543433) Homepage Journal
    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 [thinkwiki.org].

    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 [anandtech.com].
    • 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.

      Other than that, Mrs. Lincoln, how was the play?
  • by Anonymous Coward
    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 d
  • So looking at this I can't tell what happens in a dual boot situation - it describes setting up 'autostart' - does this happen at the os level?
    What i'm wondering is, since this things looks like a windows utility, will the changes stay in effect when I boot into linux? Is there a linux solution if not?
  • I would love to see if I could make my laptop a little less warm, so let's see if anyone can help:

    I am running the following:

    Dell Inspiron 8600, 1.6GHz, 768MB RAM, ATI Radeon 9600. Running Fedora Core 4 fully up to date and using proprietary drivers successfully.

    The cpuspeed daemon seems to be doing it's thing properly by adjusting stuff on the fly so I suspect it is in /etc/cpuspeed.conf that I can effectively make adjustments but I don't know where to begin tweaking. So, anyone out there already know wh
  • No performance loss (Score:3, Informative)

    by Delph1 (936230) <andreas.galistel ... m ['mai' in gap]> on Monday January 23, 2006 @06:08PM (#14543603) Homepage
    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.
  • by PHanT0 (148738) on Monday January 23, 2006 @06:10PM (#14543618)
    I work in support at a hardware company which sells some USB products. On a related note to this article, the processor isn't always the one whose voltage is dropped. When one of customers call-up using a laptop, more often then not the device is fine and it's the laptop who is underpowering the USB port in order to save battery life which is causing the problem.

    Just food for thought.
  • by yorktown (947019) on Monday January 23, 2006 @06:12PM (#14543645)
    Back in 2000, Transmeta started producing chips with Longrun [transmeta.com] 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.
  • By lowering the voltage to the processor you can not only drastically lower the heat dissipation, but also increase the battery time significantly. 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?
    • 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 Speeds

    • I've been using RM-Clock to run my 1500+ (1.33Ghz) in my laptop at 1.2V instead of 1.45V and haven't noticed any major slow-down, I would believe there is a slight decrease, but nothing near what running it at 530Mhz (lowest possible stable speed) and 1.2V would produce. I've found it to be a fantastic way to improve the battery life of the three year old battery (I could upgrade, but that costs money and RM-Clock is free.) I've noticed Sandra says my cpu can go down to 1.08V, but effectively to keep functi
  • All this for 20% does not sound worth it to me.. My time is worth more then the time it takes to save 10 min of battery life.. and my work is too important to risk my pc crashing because it is underpowered.
    • So true. The time spent wasted if your proc also underclocks in the undervolt will likely be greater than the battery life saved, putting you at a net loss. Net loss means loss in productivity, which means it was worthless. Unless youre a hobbyist just messing around, of course.
  • Help me out here.. I sure one of y'all know this:

    If a CPU (let's take a 486DX as an example) is using 10A @ 5V, it's said to be consuming 50W of power. Question is, what is it doing with all that power?

    In relative terms, electrons are pretty light little things. Sure, there are brazillians of them moving about the CPU, but their cumulative mass is still negligible. It can't take much real power to shuffle them around (nothing like rolling a giant boulder to the top of a hill) - unless of course, you acc

    • by Pyrrus (97830) on Monday January 23, 2006 @08:17PM (#14544704) Homepage
      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.

Mathemeticians stand on each other's shoulders while computer scientists stand on each other's toes. -- Richard Hamming

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