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how does undervolting workWould you believe that many computers and smartphones can run cooler and consume less power? A trick exists, called undervolting, which can increase your CPU’s efficiency with few drawbacks. If performed right, devices generally produce less heat while exhibiting improved battery performance.

The process can require a great deal of patience and confidence as the potential for disaster exists. Only the stouthearted should even make an attempt. For those of you looking for quicker solutions to reduce battery drain, check out Tim’s excellent article 7 Ways To Boost Your Cell Phone Battery Life [iPhone, Android & Other Smartphones] 7 Ways To Boost Your Cell Phone Battery Life [iPhone, Android & Other Smartphones] By far one of the most disappointing features in just about every smartphone these days is the battery life, which for most of us requires at least one charge per 24-hour period. Are you a... Read More  on mainstream methods of cooling your computer down.

This article introduces undervolting to the uninitiated, focusing on explanation, methods of implementation, the available compatible hardware and what software exists. For a more detailed guide on how-to undervolt, check out this instructional guide.

Undervolting Explained

After an intense session of Call of Duty or Modern Warfare 3, you may notice your computer or graphics processor getting unusually hot. That’s because a simple relationship exists between the the speed at which a device runs and its temperature. When you use your computer to perform CPU intensive tasks, it will run at a higher frequency, and thus produce greater heat, than it would at idle.

There’s a formula that electrical engineers use to explain this relationship. Unfortunately, I wasn’t smart enough to be an engineer so my understanding is weak, but here goes: P = V^2/R, where power is equal to voltage squared, divided by resistance.

As you can see from the equation, lowering voltage has a tremendous effect on power. But the question remains: How could it be possible for us to lower voltage while maintaining performance? Keep in mind three factors:

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  • Not all CPUs are the same: Because of the ridiculously complex manufacturing required in fabricating a processor, no two CPUs are exactly the same. Rather than responding identically to voltages, CPUs exhibit a range of tolerances. Consequently, the companies that make processors established a baseline voltage that most CPUs can use without issue. Unfortunately, this voltage is oftentimes higher than required and produces a great deal of waste heat as a byproduct. Because of this, the majority of CPUs can actually use a lower voltage a various frequencies.
  • A CPU’s speed progression isn’t linear: A computer’s speed varies from its top-rated clock cycle, typically measured in gigahertz, to its lowest possible speed. The progression between its fastest and slowest speed does not move in a linear fashion, but in a stepped pattern. I’ve seen differing terminologies for these “steps” on differing CPU architectures. For the PC (x86), I’ve seen it referred to as P-states. ARM does not appear to have a similar naming convention.
  • You can decrease a CPU’s voltage: CPUs exhibit a range of voltages tolerances across frequencies. For example, using special software you might lower the voltage (sometimes referred to as a “VID“) at different frequencies.  If too low, it will cause crashes and blue screens, so caution is advised.

how does undervolting work

Three Steps To Undervolt a Device

  • Backup Your Information: In case something goes catastrophically wrong you may get permanently boot-looped. Therefore it’s crucial to have your information backed up.
  • Gradual Voltage Changes: Whenever you lower your voltages, there’s always the possibility that it will cause a reboot. Some handheld devices enter what’s known as the “sleep of death“, which means the phone requires a hard reset. If you saved your voltages this can result in an unbootable condition, since it loads up unstable voltages. Remember to gradually move the voltages down (and never above the default value!) and then rigorously stress test at each step. However, it’s important to note that the multipliers associated with faster processor speeds undervolt more efficiently than those at lower speeds, since the highest speeds produce the most amount of heat. On mobile devices, undervolting makes the biggest difference in both energy consumption and heat production.
  • Stress Testing: After moving your voltages down one multiplier, you will want to stress test rigorously. Stress testing software for both Android and PC exists, which make this process much easier. It simply runs your CPU at the fastest possible speed, or at a range of frequencies. Simply set your undervolt value and then fire up your stress testing software.

For Desktops & Laptops

Some desktops and laptops can alter their voltages through their BIOS. Different motherboard manufacturers, unfortunately, use differing terminologies: Some use the term “voltage offset“, which reduces voltages uniformly across all steps. Other boards only reduce voltages at the highest CPU frequencies – you should Google your motherboard’s make plus the search term “undervolt” or “voltage offset“.

For example, my undervolt settings from my EFI (it’s basically a BIOS):

how to undervolting cpu

Intel CPUs: Unfortunately, Intel chipsets, Sandy Bridge and later models, do not benefit in any substantial way from lowering voltage. While my own experiences show some impact on temperature, the experts believe otherwise. The most common method of undervolting older Intel CPUs is ThrottleStop for the Windows OS.

Throttlestop lowers voltages across a range of CPU frequencies – simply check the “Set Multiplier” box then reduce the “VID” number to drop voltages.

how to undervolting cpu

AMD CPUs : particularly its Brazos, Llano and Trinity lines, can undervolt with great effect. One of the best examples is the undervolting software available for the Brazos series of CPU/APU. The software used to manipulate voltage values is known as BrazosTweaker. There’s also FusionTweaker. Users report up to 30% reductions in temperatures and solid increases in battery life.

For AMD chipsets, other voltage manipulation methods exist, such as PSCheck and AMD Overdrive. However, although PSCheck is the best program, it’s also the hardest to get hold of. I ended up biting the bullet and installed a zip from a complete stranger’s Dropbox—that’s always a terrible idea and you should never do that, unless you’re me. In which case you make regularly poor decisions and installing strange files from sketchy sources is the least of your worries.

Stress-Testing: To stress-test your device, simply lower your voltage by a single step and then fire up the stress testing software. In my experience anywhere from 5-10 minutes of testing is sufficient. If the computer crashes or freezes, move the voltage back up at least one step before moving onto the next multiplier (sometimes referred to as a P-State, pictured below). Continue repeating the process at each stepping point, lowering the voltage until instability occurs. Notice that as frequencies increases, so too does voltage.

how to undervolting cpu

The best software for stress-testing is Prime95. Prime95 runs complex mathematical formulas on your computer, which causes the the CPU to run super hot. If you’ve set the voltage too low, your computer will crash and you’ll know the absolute lowest limit of your processor’s voltage tolerance. Approximately 5-10 minutes of stress testing should weed out incorrect voltages.

From the Prime95 “Run a Torture Test“, make sure to select “Small FFTs“.

undervolting cpu

We’ve discussed undervolting on MakeUseOf before for laptops. Also, read about Tina’s breakdown of some mainstream solutions How To Fix An Overheating Laptop How To Fix An Overheating Laptop Read More  for getting your heat under control.

Tablets, Smartphones & Android Powered Devices

Before attempting to undervolt your device, you must have root How To Root Your Android Phone With SuperOneClick How To Root Your Android Phone With SuperOneClick Read More  access (link goes to SuperOneClick) and you should have installed a custom ROM How to Find and Install a Custom ROM for Your Android Device How to Find and Install a Custom ROM for Your Android Device Android is super customizable, but to fully take advantage of that, you need to flash a custom ROM. Here's how to do that. Read More  supporting undervolting. While, technically, you only need a custom kernel that supports UV, most custom ROMs include a custom kernel.

Most cell phones with a custom kernel and the right software can undervolt – however, doing so requires special firmware, or software that exists at a level higher than the operating system. Firmware is stored on solid state memory in an area normally inaccessible to the end-user. However, if you have the right firmware, some software can modulate the voltage fed to the CPU.

My favorite software for undervolting is IncrediControl. Just run the app and select the “SVS” tab from the top menu bar. From there, you must use extreme caution. Proceed to lower voltages one step at a time. I recommend only lowering the voltages on the two or three highest frequencies; as indicated by the power equation, reducing voltages at higher frequencies has a greater impact on overall heat production.

undervolting cpu

Stress-Testing: For stress-testing, to my knowledge there’s only one app worth using: StabilityTest. Simply choose either “Classic Stability Test” or “Scaling Stability Test“. If you only intend on undervolting your highest CPU frequency, the classic test should suffice. However, if you plan on undervolting a range of values, go for the scaling test.

how does undervolting work

Conclusion

Cooling down your devices and getting better battery life takes only three steps: First, backup your device. Second, make gradual voltage adjustments. Third, stress test each time you make a voltage adjustment. For Android devices, this requires that you have root access and have installed a custom ROM. For computers, you must have a newer AMD chipset, such as Llano, Brazos or Trinity. On Intel system, you must have Core2Duo or thereabouts.

Remember to never raise your voltages above the default value. Raising your voltages will likely destroy your computer.

Does anyone else love undervolting? Let us know in the comments.

Image Credits: Lightning via MorgueFile.com; Motherboard via MorgueFile.com

  1. Jonathan A
    May 25, 2013 at 2:25 am

    How is this different from overclocking?

    • Kannon Yamada
      May 25, 2013 at 3:59 am

      I'm really glad you asked this question - undervolting is compatible with overclocking. Think of it this way - manufacturers set a specific voltage that's supplied to the CPU, which varies across frequencies. Undervolting decreases the CPU's voltage below what the manufacturer set as the stock voltage.

      Overclocking increases the maximum frequency that the CPU is capable of hitting. When you overclock a 2 GHz CPU, you raise its maximum frequency above 2 GHz.

      Believe it or not, you can sometimes do both! However, I would add that undervolting is a lot easier to do than overclocking.

      • DalSan M
        May 26, 2013 at 10:02 am

        Also, if the processor (or GPU) isn't unlocked (able to change settings easily), then undervolting can still be done in most cases. In most cases, undervolting AMD processors is a good thing to do since they tend to run hotter than most Pentium processors. Care should be taken when changing any processor settings, but undervolting is safer than most other changes that can be made.

  2. DalSan M
    May 22, 2013 at 6:40 pm

    One thing to note: yes Android devices have to be rooted in order to change voltage and processor settings, but installing a custom ROM is not a requirement. Flashing a custom kernal, on the other hand, might be the minimum that must be done in order to allow the changing of processor settings including undervolting, underclocking, overclocking, and changing the governor type. Some custom ROMs do not allow one to change CPU settings since the stock kernal is used for the ROM. If installing a custom kernal, then be sure that it matches the Android version that is installed on the device.

    • Kannon Yamada
      May 22, 2013 at 8:38 pm

      I did mention that, but I should have been clearer. Many custom ROMs don't include kernels that can be undervolted. Also the majority of kernels don't have UV provisioning. I don't know why, either, because it's a big deal on any mobile device.

      I should have mentioned the dangers of installing a custom kernel, though. Thanks for the comment.

  3. vineedcool
    May 22, 2013 at 3:19 pm

    awsum article i will give it a try on my friends Lappy,,,he needs it!

  4. Guy McDowell
    May 22, 2013 at 12:25 pm

    Nice work! Concise, yet even a novice could follow what you're saying. I might have to look at doing this with some servers.I wonder what the power savings could be?

    I'll have to run the equations, and get back to you on that.

    • Kannon Yamada
      May 22, 2013 at 8:49 pm

      Thanks Guy!

      I have no idea how much power an undervolted server would save. I would bet money that undervolting could make a single digit impact on yearly power costs though. :-)

  5. sriramv24
    May 22, 2013 at 10:29 am

    Nice post! Thanks for the information.
    You have mentioned that Sandy Bridge and other related processors are not affected by undervolting. Could you please provide some links as to why it is so?
    Thanks!

  6. Bill Clayton
    May 22, 2013 at 2:23 am

    Love the article. But check out this one. It's about the power of today's mobile computers but it mentions a process called "computational sprinting," which improves computing performance AND extends battery life.
    http://www.engin.umich.edu/college/about/news/dme/mightymobile/

    • Kannon Yamada
      May 22, 2013 at 9:20 pm

      Thanks Bill! Fascinating article. Also, that is easily one of the most beautiful websites I've ever seen.

      It's probably my own bias speaking, but I hope that this is one of those rare instances where battery and materials science jump ahead of computational increases.

  7. Nevzat A
    May 21, 2013 at 6:44 am

    I love the idea, but many low level utilities requires you to know the internals about your hardware. Speedfan was one of them, requiring me to know the exact chip used on motherboard and I had no idea when I had tried it years ago. Since then I only trust built-in utils and power management profiles on windows.

    • Kannon Yamada
      May 21, 2013 at 8:57 pm

      Thanks for the comment Nevzat!

      Speedfan's low compatibility has always been a problem for me. Although when it works, it works great.

      Undervolting doesn't actually require any specific knowledge of your computer's internal layout. But it does require certain kinds of hardware. Mainly ARM, Core2Duo and many AMD chipsets.

      Out of the many computers in my household, all of them are undervolted. Core2Duo is particularly easy to work with. ARM with the Android OS, with a custom kernel, is another easy to modify setup.

      But because of the risk involved, I cannot recommend undervolting for everyone. If it's done wrong, there's a chance for bootloop.

      • Nevzat A
        May 22, 2013 at 6:14 am

        Many thanks for the comprehensive answer Kannon Yamada.

  8. Zhong J
    May 21, 2013 at 3:18 am

    Sounds interesting, to me feels like making the computer use less power. But how would you be able to configure this setting to a BIOS where you cannot access the Voltage configuration and in a Linux environment?

    • Kannon Yamada
      May 21, 2013 at 9:00 pm

      There are some Linux utilities that allow for undervolting, but again, they have very narrow ranges of hardware compatibility. In generally, I would advise against undervolting an AMD or Intel chipset on a Linux platform because my own experience is with ARM and Linux and x86 and Windows.

      http://www.linux-phc.org/

  9. null
    May 21, 2013 at 1:17 am

    I really enjoyed reading this post. As I read, I kept saying I would really like to try this. However, really checks in and I tells me that I like my laptop and now is not a good time to go tampering.

    • Kannon Yamada
      May 21, 2013 at 9:01 pm

      Thanks! And good thinking - if you like the way your computer currently performs, then don't bother trying to undervolt.

      But if you start suffering from chronic overheating, it always nice to have additional options. :-)

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