Does CPU speed drop when only on battery?

Discussion in 'MacBook Pro' started by imorton, Jul 13, 2011.

  1. imorton macrumors 6502

    Aug 21, 2010
    Some of my older Dell laptops use to drop in CPU speed when operating only on battery power.

    Does the 2011 13" core i5 Macbook Pro's reduce CPU frequency when running solely on battery power?

    I know that some of the Macbook's reduce the CPU speed when removing the battery, but I wonder if the Sandy Bridge core i5 use some type of Speedstep technology to throttle down the cpu when removing the AC power.
  2. blackbinary macrumors member

    Jul 2, 2011
    I'm not sure how you would expect to get 5-9 hours of battery life if this was not the case.

    It's not so much that they drop the CPU speed when on battery, but instead it is dropped when your not doing anything intensive (for example, it probably isn't going very fast when your just browsing macrumors). From there, it will speed up to regular speed when under some strain, and then turbo boost will kick in and decide how much it can overclock based on the current environment (temp etc)
  3. alust2013 macrumors 601


    Feb 6, 2010
    On the fence
    The CPU will downclock itself when not doing anything intensive, regardless of AC or battery power. For example, I have a 2.4GHz C2D MacBook, but that's just its max operating frequency, it normally runs at 1.6GHz under light load. The CPUs with turbo boost list the stock frequency as the highest frequency that will not be limited by heat or load, but it can either be higher or lower than that. It's not limited to a lower frequency on battery though.
  4. imorton thread starter macrumors 6502

    Aug 21, 2010
    So are you guys saying that the CPU operates the same whether on AC power or on Battery power?

    If I read things correctly, the CPU scales up/down depending on demand/load, and it performs the same whatever power source it is on?

    I just thought that it would run at 2.3 Ghz speed when on AC power, and reduce the CPU frequency to a reduced CPU speed (ex: 1.6 GHZ) when on battery.
  5. Deedolito macrumors regular


    Aug 19, 2010
    A MBP does not cut it's computing power down just because you don't use the power adapter.
    Some energy saving options like screen darkening, etc. will be preset, but it's not like with some Windows notebooks, which cut 50% power off the CPU to save battery energy.

    These "up to 9h" statements are - let's say... theoretical conditions that can maybe reached by the user *cough*.

    There are a lot of smart power saving options like the 2nd GPU, but they are enabled whether you use the power adapter or not. Energy efficient machines that don't steal your time by slowing themselves down if you need full power.
  6. Ephmreal macrumors newbie

    Jul 14, 2011
    Yeah, like if I turn my screen/backlight all thew way down, turn off all my applications etc. i can potentially get my battery to last about 12 hours.... but sitting for 12 hours with nothing to do but watch the battery timer count down isnt that much fun...
  7. Deedolito macrumors regular


    Aug 19, 2010
    Totally agree :D
  8. windowstomac macrumors regular

    Jun 23, 2011
    As an ex Windows user I couldn't be more delighted with the battery life on my new MacBook Pro :)

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