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."

Comments

Underclocking

[selfabuse]

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.

Re:Underclocking

[mjh49746]

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

"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."

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?

[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:Counter productive maybe?

[bigtrike]

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 experiment with dropping the voltage however, which may have produced a net savings.

Re:Counter productive maybe?

[yppiz]

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

Re:Counter productive maybe?

[Marxist Hacker 42]

Photo editing, for the most part, is more memory intensive than CPU intensive.

Re:Counter productive maybe?

[evalf]

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.

Re:Counter productive maybe?

[frdmfghtr]

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.

Re:Counter productive maybe?

[Y0tsuya]

I think he meant that processor designers (and chip designers in general) design their chips to work over a certain range of operating conditions. In order to accomplish this they build in margins of safety and simulate their designs to death using expensive workstations or clusters. After production they get speed binned with elaborate tests using multi-million dollar machines.

Of course many users think they can do better with their over/under voltage/clock regimes, all the while claiming that it's a conspiracy by the processor vendors to deliberately throttle down their CPU. But all they're doing is wiping away the safety margins built in by the engineers. It's kind of like ricers cutting springs in their hondas. Never mind that Honda engineers spend thousands of man hours and million of dollars testing, simulating, and tuning their suspension on their expensive workstations and test tracks. I see their cars bobbing up and down like low riders over small imperfections on the highway and shake just my head.

In short, people who think they're smarter than engineers, usually aren't.

Computer Performance

[ranton]

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?

--

Re:Computer Performance

[drinkypoo]

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.

No Con's?

[randomErr]

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?

[obious]

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.

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.

isn't this what speed step did back with the PIII?

[ulysses38]

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

[Anonymous Coward]

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

[AKAImBatman]

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.

Re:Bad Idea

[serbanp]

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

[serbanp]

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.

Re:Bad Idea

[F00F]

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-dependent.

In order for a CPU to work properly, an awful lot of "digital ballet" needs to be happening, billions of times per second, in perfect harmony. Failing a single setup or hold check on a clocked logic gate leads to erroneous bits entering your data and control streams. Quite a few logic blocks, implemented in quite a few different transistor-level CMOS techniques, have different timings depending on what data is flowing through them at the time -- i.e. whether certain bits are zeroes and others ones, or whether the bit transitions from a one to a zero at the same time as an adjacent wire is switching, etc.

What I'm saying, of course, is that if you "spend a lot of time to find out what is the lowest safe voltage", and then (oops) you plug in a USB peripheral that you weren't using before, or (oops) your room heats up a little, or (oops) you use a laptop cooler to get it off your lap a little (setup and hold times, as well as clock and data paths are voltage dependent y'know...) or (oops) you access an unusual data pattern in a program you haven't run in a while, or (oops) you use your laptop on an airplane, your happy little CPU (that you just had to eke out that last little bit of thermal margin from!) starts failing. Quietly, sometimes.

If you're lucky, Windows just crashes -- but manages not to trash your hard drive while doing so (remember, this is weeks or months after you ran your little three-day burn-in marathon "torture test"). But in a not-so-pleasant outcome, your data just starts quietly... rotting. Binary file formats start getting corrupted. Programs stop running. Checksums start failing. Spreadsheets start changing quietly behind your back. I grant you that on a Windows-based laptop this sort of thing could generally be considered the norm (due to virii and spyware and so on), so you might not really notice.

But fortunately for the retarded selves of the people "publishing" (I use the term loosely) this crap, there are thousands of engineers at Intel and AMD running detailed and comprehensive timing simulations of all of the tens of millions of transistors in those teeny-tiny CPUs. They can't possibly EDAC- and parity-protect every net in the design, but they do run static and dynamic timing checks, with probabalistically-developed parasitics and 3-dimensional noise parameters. They consider crosstalk and electrical noise, process variability, and electromigration. They run extensive tests on the CPUs at the wafer and package level to detect slight variations in current consumed during carefully-chosen JTAG test vector execution. They speed-bin and scrap parts that don't pass the multi-billion-dollar test regimens that they spent close to a decade perfecting, and use the detailed results to craft application notes and engineering design guidelines that they feed to their OEM partners, who in turn carefully couple the CPUs to circuit boards with traces perfectly matched to one another, as well as to the impedance characteristics of the solder they're using, and attach them to advanced power supplies and controllable oscillators.

And then you go ahead and download a shitty little ninety-nine cent program off teh unternet and procede to pick your own CPU voltage that "seems to work OK".

Yeah, good luck with that. Sounds like a plan to me. There once was this handy expression about fools and money -- I guess "data" is just the modern substitute.

Been doing this for almost a year with CHC

[Anonymous Coward]

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.

laptops already have step by step instructions

[method77]

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.

Parent is a Bad Idea

[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.

Re:Parent is a Bad Idea

[StikyPad]

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.

Re:Parent is a Bad Idea

[techfury90]

But most CPUs since the late 1980s are CMOS.

I'm not sure which is more surprising

[Marxist Hacker 42]

That the CPU can run at a lower voltage- or that voltage of the CPU on a modern motherboard is SOFTWARE Selectable.

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.

Re:18% -- that's really funny

[Da Zeg]

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.

Re:18% -- that's really funny

[Formica]

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.

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:18% -- that's really funny

[homesandgardens]

Actually, the difference is that Celcius is a linear scale and Fahrenheit isn't. 64 F is not half the actual temperature of 128 F. With pounds and kilos you can divide or multiply either by one number to get the other, not so with F and C.

Re:18% -- that's really funny

[HardCase]

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 important number.

-h-

Re:18% -- that's really funny

[Odin's Raven]

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.

Re:18% -- that's really funny

[ian_mackereth]

Verbing weirds nouns.

What for?

[Poromenos1]

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?

[AngelofDeath-02]

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 need to downclock just because you lowered the voltage, but you may introduce system instability ...

That's usually what happens when you overclock without increasing the voltage as well.

Re:What for?

[Lehk228]

to communicate a wifi card transmits and recieves. yes they do use a lot of power.

Why?

[Eightyford]

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

I modded my Dual-Heel Processor

[digitaldc]

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.

Too much misinformation here.

[TheGuano]

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!

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!

Lowering the voltage does not affect performance

[sammydee]

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 possible for a given clock speed to reduce heat output.

I do this too.

[Anonymous Coward]

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.

Nothing new for now...

[Razlor]

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.

Undervolting is not underclocking.

[Destoo]

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.

There is no performance difference

[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 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_

No performance loss

[Delph1]

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.

Re:It's 18% cooler only in Celsius

[pierreTheBear]

Ok, so my iMac G5 is running at about 50 deg C. That's 323 degrees Kelvin (ie, total thermal energy above absolute zero).

An 18% reduction in absolute temperature would reduce my processor to 264 deg K... that's equal to -9.15 degrees Celsius.

My kitchen freezer can't even get that cold! If I undervolted my iMac, I could be chillin' my b33r right now as well!

USB often has its corners cut...

[PHanT0]

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.

Re:isn't this what speed step did back with the PI

[krgallagher]

"isn't this what speed step did back with the PIII"

This is what AMD did with their PowerNow!(TM) technology. It dynamically adjusts CPU power consumption based on CPU load. According to AMD, it can reduce CPU power at Idle by 75%. I know on my laptop, I can hear the fan speed up and slow down based on the load on the CPU.

Transmeta's LongRun technology

[yorktown]

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.

Re:Undervolting is NOT the solution

[onkelonkel]

Say What?? Either you are trolling or you fundamentally misunderstand Ohm's law.

Resistive loads (which, to a first approximation, a CPU is), don't "demand...Watts", they "draw current". The load resistance doesn't change, so Ohm's Law I=V/R says that if you drop the voltage, the current decreases. Drop the voltage 5%, you DECREASE current 5%. Your total power (V * I) is now decreased by 10%.

As for "screw up the reference voltage", this is and remains system ground, or 0 V. Yes, at some lowered voltage, the CPU will cease to operate. Assuming the CPU still runs, a logic level of 2.85 V is just as good as 3.0 V.

Sacraficing speed for power?

[Dream1979]

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?

Re:Sacraficing speed for power?

[Delph1]

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.

Re:Sacraficing speed for power?

[VirionNW]

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 functioning (and not reduce the clock) it needed to be at 1.2V, minimum. The voltage and clock speed aren't directly tied, so it leaves some wiggle room, it would seem, as both experience and this article show. Also, a key thing I noticed is that even if the lower voltage may hurt preformance, my FSB is at full speed when I clock to max with lowered voltage, unlike the reduced FSB at lowest clock with lowest voltage, so even if I lose some preformance, it still beats the pants off the normal reduced power settings. Also, if anything, it at least keeps my fan quiet for longer, it's got a nice "replace me" buzz going and I haven't the time to do the work, so this works as a nice side effect.

PowerDemandign components

[pscottdv]

No. He's talking about the new PowerDemanding (TM) components
They're designed to increase current to meet their power demands.
If they can't get their power that way, they're designed to lobby
Congress.

Ok all that for 10 min of battery life?

[mdman]

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.

Re:Ok all that for 10 min of battery life?

[mkosmo]

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.

Re:Interesting... How much extra battery life?

[TheGuano]

My own tests with Arctic Silver 5 on 15" Thinkpad T42p:

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).

Re:CPU efficiency vs. heat rejection

[Pyrrus]

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.

Similar human procedure

[No2Gates]

George W. Bush was the first recipient of this in human form. The synapses were reduced by 80% to save energy.

Rovclock

[wiresquire]

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.

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

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.

Easier Solution:

[thepotoo]

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...