Underclocking a MacBook Air

Several folks contacted me this morning to let me know about more MacBook Air users who have discovered that underclocking their CPUs keeps the processors cool enough to avoid the core shutdown.

The author suggests an application called ‘Coolbook’ which purports to underclock the laptops CPU by lowering the voltage supplied to the processor and by more agressively throttling the speed of the CPU.

Knowing what the Santa Rosa platform is up to, this now makes a certain amount of sense: Rob underclockspowers the CPU by 20%, and further limits the CPU to 75% of max speed (1.2GHZ) while on battery, which in turn has a dramatic cooling effect while only minimally affecting performance. The cooler CPU avoids the shutdown threshold and therefore the UI is more stable.

It appears to be better to suffer 25% degradation all the time on battery, instead of 50% (or more) some of the time. The OS requires a certain minimum processing threshold, but it’s really the CPU threshold that’s of concern. Underclocking appears to keep the load and temperatures under that threshold.

At least one person who emailed me asked if I thought underclocking is a good idea. I honestly have no clue; I’d like to say no, always stick with the manufacturer’s specs. But in this case those specs suck, and if you can do something about it (and undo the underclocking if anything goes wrong), it may very well be worth it.

For more on the core shutdown issue, please see my MacBook Air Log. I’ll continue to post more information there as it comes in.