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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.
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.
I used to have a better sig but it broke.
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?
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-- All that is necessary for the triumph of evil is that good men do nothing. -- Edmund Burke
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?
You say things that offend me and I can deal with it. Can you?
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.?
my sig is an honor student
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.
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.
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.
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.
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.
He who knows best knows how little he knows. - Thomas Jefferson
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!
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.
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
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.
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.
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!
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.
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.
He's talking about the videocard in this particular case.
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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.
No, I am not an English major. My posts are subject to typos and incorrect grammar. Do not expect perfection.
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.
None of them can see the clouds; The polished wings don't care.
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.
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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).
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.
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.
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
So does Anonymous Coward have good karma?
The downside is that it takes like forever to load Word...
Obligatory Soundbite Catchphrase
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.