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I'd like to do so to reduce heat / extend battery life when on the road.

Are there any apps I can use (like Rightmark for the PC) to underclock/undervolt a Mac? Conversely, would does such an app exist to overclock as well?

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4 Answers 4

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Coolbook will do it, but might have difficulties with newer MBPs. Also, the latest version at least has a $10 license fee.

I would be inclined to think that there would be a Unixy/CLI utility for this, although I don't know one off-hand.

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As a start, be sure to set your Energy Saving settings (in the System Preferences) to Save more energy. That should extend battery life some.

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There's a kernel extension and a free app for controlling Intel SpeedStep using "sysctl"

http://code.google.com/p/xnu-speedstep/

To see which frequencies are available:

sysctl kern.cputhrottle_freqs

To switch frequency:

sudo sysctl -w kern.cputhrottle_curfreq=YYYY
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CPUs are already throttled down in energy saving mode (as noted by dyve), you probably gain more by ensuring excess background tasks are killed.

Also, CPU power consumption nowadays is quite low compared to other components, most notably the screen (backlight) and rotational harddisks. See also Laptop Battery Life: How Wireless Affects Power Consumption and Component-wise Energy Breakdown of Laptop, some articles on this topic.

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