Undervolting a Laptop 262
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."
Underclocking (Score:5, Informative)
lol (Score:3, Informative)
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.
Bad Idea (Score:2, Informative)
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:Computer Performance (Score:5, Informative)
Been doing this for almost a year with CHC (Score:2, Informative)
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 (Score:3, Informative)
What for? (Score:3, Informative)
Re:18% -- that's really funny (Score:2, Informative)
Nothing new for now... (Score:5, Informative)
Undervolting is not underclocking. (Score:5, Informative)
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].
There is no performance difference (Score:2, Informative)
Also, for the Gentoo users: HOWTO Undervolt a Pentium M CPU [gentoo-wiki.com].
mnemonic_
Re:18% -- that's really funny (Score:3, Informative)
Re:Undervolting is NOT the solution (Score:1, Informative)
If you lower the voltage, the components will simply stop working as you go below their operational rate.
Put it another way.. as you approach zero volts, does current approach infinity? The answer is no.
No performance loss (Score:3, Informative)
Re:Bad Idea (Score:5, Informative)
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:No Con's? (Score:2, Informative)
Transmeta's LongRun technology (Score:3, Informative)
Re:Bad Idea (Score:2, Informative)
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:Counter productive maybe? (Score:3, Informative)
Re:Underclocking (Score:3, Informative)
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."
Re:Parent is a Bad Idea (Score:3, Informative)
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:Sacraficing speed for power? (Score:2, Informative)
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:Counter productive maybe? (Score:5, Informative)
Re:Counter productive maybe? (Score:5, Informative)
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:Interesting... How much extra battery life? (Score:4, Informative)
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:18% -- that's really funny (Score:3, Informative)
I don't want to be pedantic, but if I did, I'd consider the change in temperature as the important measurement. After all, there's not much chance that the computer will be working at anything near 0K. So, consider the "zero point" to be room temperature, or about 295K.
So, at normal voltage, the peak CPU temperature changed by 56K. With reduced voltage, the peak CPU temperature changed by 42K.
1 - (42K / 56K) =
-h-
Re:CPU efficiency vs. heat rejection (Score:5, Informative)
Re:What for? (Score:3, Informative)