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Mac/PC users: processing power affected by battery power?

  1. May 16, 2012 #1


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    Has anyone heard of a feature whereby display processing power is linked to system power levels ?eg.: if you're operating on battery rather than wall plug, can that have an effect on whether you get full acceleration when watching videos?

    My sister claims that, on her Mac, when the battery is running low, the video will not be as smooth (choppy, audio cut-outs).

    I think this is complete nonsense, but it's occurred to me that it is not totally impossible that a computer system might disable some high-performance features such as video acceleration in an effort to conserve battery power.

    Anyone ever heard of the such a thing?
  2. jcsd
  3. May 16, 2012 #2
    well i know for a fact that the system will step down the multipliers on the CPU to reduce power usage and heat generation. the GPU may very well be doing something similar to conserve power/reduce heat.

    I'd have to look it up so be certain but i dont think its unreasonable to think that the OS/BIOS might be disabling or under-clocking components to extend the battery life as much as possible. EDIT: especially when the battery is low, give the user a chance to save his/her work before the thing dies.
  4. May 16, 2012 #3
    When I am doing computations in Mathematica (on a PC running Ubuntu) on battery power, they are performed 10 times slower!
  5. May 16, 2012 #4
    Well , make sure the portable computer is not in power-saving mode.
    In case it is , then you may face glitches while playing games and running 720p+ videos.

    Most modern day portable PC's are equipped with multiple GFX cards.Speaking precisely , they generally have on-board gfx alongwith Dedicated or Discrete class GPU.
    -Now as per system configuration the PC may switch b/w Discrete class/Dedicated GPu and Onboard graphics whenever required.
    I am not sure but certain systems may support the ability to automatically manage this switching based on requirements and power supply.(I have one ASUS laptop with twin GPU).Some of the laptops(including mine) even have turbo-boost technolgoy that uses more power to deliver performance.

    Also the more CPU/CPU/RAm you will utilise , the more heat will be generated and this will lead to increase in the supply of Power to FANS.
    In case the FANs don't get enough supply of power (don't speed up) , the system will heat up and most probably will lead to performance issues.

    Some processors are already overclocked from manufacturer's end.As Routaran said , they will most probably step down some of its multipliers in order to save power , if configured in power saving mode.
    Chances are that you will face this frequently in a high-end performance laptops(equipped with multiple COre CPU's and GPU's.)
    As far as I know in low range lappies/netbooks the processor has 18 watt TDP (amd e450) , whereas high end processor like Core I-7/I-5 sticks around 65+Watts of TDP or even more.

    Btw , Try to override the configuration to performance mode , though it will drain the Battery but it will not compromise with the performance.
    Last edited: May 16, 2012
  6. May 16, 2012 #5


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    Thanks. You've answered my question. It's not about whether I am wrong, it's about whether I could be wrong. :bugeye: (I know, I know. Crazy talk.)

    I must concede to my sister that it is plausible that her computer might indeed slow down when she is on battery power and/or running low on battery power (therefore, she is not crazy for thinking so).
  7. May 16, 2012 #6
    Yes she might be very much correct about her observation about this .But if this happens when playing a low-resolution video on a hig-end/medium laptop , then there must be some serious issues.Also the audio quality should get that worse or unpleasent.

    Although its possible to resolve this issue of low performance , but it comes bundled with the drawback of poor and unstable Battery life.

    When throlttled to max clock., the battery consumption can increase upto 40-50% faster.

    Also I forgot to mention that features like Intel's SpeedStep technology is something that is not controlled by OS itself , it can be controlled only in BIOS settings.
    Laptop's with that technology usually perform better with AC power plugged in , since they throttle the CPU to a large extent , this is similiar to Turbo-Boost.
  8. May 16, 2012 #7


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    Thanks. Little comfort. I have the unpleasant task of conceding to my sister.
  9. May 17, 2012 #8


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    A weak battery can definitely reduce cpu, as well as gpu performance. It depends on your MB. A weak battery can actually destroy a laptop over time. Remember all the warnings about running your desktop on an underpowered PSU? The same principle applies to battery power. I would replace the battery, or only run the laptop while on the charger.
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