How does coolbook actually work?

Discussion in 'MacBook Air' started by byke, May 24, 2010.

  1. byke macrumors 6502a


    Mar 29, 2007
    LDN. UK
    I have had a copy of coolbook, since I first bought my MBA rev B .... and to be honest I never figured out if it made any difference and how to set it up.

    So my question is, how does one set it up?
    Is it just a question of trial and error or is there a specific way to set it up?

  2. Christer macrumors newbie

    Aug 7, 2008
    I have a rev A MBA. Early on, when these core shutdown problems started to crop up, I did some tests and found that my machine experienced core shutdowns under artificial loads (double "yes >/dev/null" processes). Didn't really have any problems with the machine outside that.

    However, I did end up replacing the thermal paste and purchased a coolbook license to see if I could solve the issue. To me, it made a pretty significant difference and my core shutdowns were a thing of the past.

    However, after a couple of OS upgrades (running Snow Leopard on it now) Coolbook is no longer active and the CPU runs at the stock voltages. The other day, I ran some flash video and tried the "double yes" test again for some time and my CPU temp ended up in the 75-80C range without any cure shutdowns.

    To be honest, I am simply not worrying about the temperatures anymore.

    To answer your question though.. What Coolbook does is somewhat of a reverse-overclocking. You configure the CPU to run at a lower voltage than the fairly conservative defaults. The net effect of this is that the CPU runs cooler (I think I read somewhere that there's a quadratic relation between voltage and temperature) when you reduce the voltage. The downside is that if you reduce the voltage too much, your computer gets unstable (unable to start up, or crashes randomly).

    Setting up the voltages is quite time-consuming. What you want to do is to reduce voltages step by step and make sure you test extensively after every change. For the max frequency of your CPU, it's not all that hard to find ways to test (flash videos, games, "double yes test", coolbook's cpu load setting), but I found that it's a bit tricky to test the middle frequencies over a longer period of time (apart from coolbook's own short test).

    The effect of the optimization is also dependent on how you use your computer. If you're surfing (flash-free) sites mostly, or doing light office-style work your CPU will most likely be sitting at the lowest frequency possible for your machine. If so, undervolting is not going to help you at all since you can't undervolt the lowest frequency (or at least I didn't figure out a way to do that). In this case, the only way to reduce temperatures would be thermal paste replacement (or well, certain hardware hacks come to mind but these aren't really my kind of thing).

    Bottom line is that undervolting using Coolbook is mostly a trial and error process, where you have to spend a fair amount of time to find the lowest voltage settings that give you a stable machine.
  3. Cheffy Dave macrumors 68030

    Cheffy Dave

    Feb 5, 2007
    Sunny Florida, on the Gulf Coast in Homosassa Fl
    EXCELLENT answer!:cool:
  4. byke thread starter macrumors 6502a


    Mar 29, 2007
    LDN. UK
  5. itripped macrumors member

    Apr 25, 2010
    The only thing I would add is that undervolting is not the same as underclocking. Underclocking would be the opposite of overclocking, where you set the clock speed to be less instead of more. Undervolting maintains the clockspeed as a constant but reduces the voltage. The theory is that factory settings are typically set a little higher than what is required for given clock speeds and that if you tweak them down a bit the end result is cooler temperatures. This in turn reduces the need for the fans to kick in as often. Using less power should translate into longer battery life.

    Underclocking does not make your computer slower. It is an effort to trim back any potential excess voltage for given clock speeds. I am pretty new to all of this so if I am wrong in any of this I'd appreciate the correction.
  6. Huubster macrumors regular


    Mar 1, 2010
    Underclocking does make the computer slower. You probably meant to say that undervolting does not make the computer slower.
  7. MacRuler macrumors 6502

    Apr 16, 2010
    i have coolbook, and was wondering why doesnt it allow the macbook air to run at 600mhz? i mean if that speed does not work why would the option be there? thanks

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