MacBook Air Core Shutdown
April 2, 2008
I have been using a MacBook Air as my sole laptop for a month or so now. In general I feel very positive about my experience with it. However, there is one issue that seems to be plaguing myself and other MacBook Air owners. When taxing the CPU for extended periods, the MacBook Air shuts down one of it’s cores to prevent overheating. The easiest way to reproduce the problem is to watch a few YouTube videos. After approximately 15 minutes the Mac OS X Activity Monitor clearly shows only one core running. Within a few minutes of the CPU load being lightened, the dormant core springs back to life.
While running on only one CPU core, the MacBook Air is barely usable. The UI becomes jittery and the onscreen trackpad pointer jumps around.
While trying to find a solution to the problem I came across this forum post. 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. My initial reaction was one of extreme skepticism. Alarm bells were ringing. While I consider myself a geek I have never dabbled with overclocking of CPU’s and have never even heard of underclocking. But after reading five pages of positive responses I decided to take the plunge and install ‘Coolbook’.
Firstly, let’s describe the applications UI as abysmal. There is no getting away from it. Maybe it would make more sense to someone with experience in underclocking but the whole point in a GUI is to assist the uninitiated in achieving their goals without having to resort to technical manuals. Needless to say I had to resort to the manual which is thankfully quite good.
After tinkering with the various parameters and following the advice of others on the forum I settled on the following settings…
When power adaptor is plugged in…
600HMz = 0.9V
800MHz = 0.9V
1200MHz = 0.9V
1400Mhz = 0.9V
1600Mhz = 0.95V
When the MacBook is running on battery…
600MHz = 0.9V
800Mhz = 0.9V
1200Mhz = 0.9V
This lowers the voltage supplied to the CPU by 0.2V. Also of note is the removal of the 1400MHz and 1600MHz setting when running on batteries. This has had the following results…
Before Coolbook
Approx CPU temperature under light load 52C
Approx CPU temperature under heavy load 75C
Fan speed under light load 2500rpm
Fan speed under heavy load 6500rpm
Battery life under light load - 3.35
After Coolbook
Approx CPU temperature under light load 43C
Approx CPU temperature under heavy load 62C
Fan speed under light load 2500rpm
Fan speed under heavy load 4250rpm
Battery life under light load - 4.25
Since installing Coolbook, my MacBook Air has suffered no core shutdowns, it has run significantly cooler to the touch, it is quieter (as a result of the lower fan speeds) and it lasts almost an hour longer than usual when running on battery power. As of yet I have found no downsides and I have not experienced any instability.
There is some debate about the possibilities of damaging the CPU by underclocking it. My research leads me to believe that such damage is unlikely and that using too low a voltage will simply result in OS instability. However, I am not advising anyone else rushes into underclocking their MacBook Air. All I offer is my experience with ‘Coolbook‘ for those who might be interested 
I will update this post should my experience change over the coming weeks.
Entry Filed under: Apple, Hardware, MacBook Air. .
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1.
David Nydegger | April 4, 2008 at 12:15 pm
Hi thanks for the post about Coolbook. I underclocked my Macbook Air with similar settings to yours. Now top CPU heat is around 64 degrees (celcius). No more freezings of my air, not even with an external monitor attached..
2.
plasmadesign | April 4, 2008 at 2:49 pm
No problem. How is your battery life following the underclocking?
3.
MacBook Air Core Shutdown&hellip | April 5, 2008 at 4:28 am
[...] kay123 wrote an interesting post today onHere’s a quick excerptI have been using a MacBook Air as my sole laptop for a month or so now. In general I feel very positive about my experience with it. However, there is one issue that seems to be plaguing myself and other MacBook Air owners. … [...]
4.
Kirk | April 11, 2008 at 12:54 pm
Apple’s recent firmware update seems to have the same fan and temperature results as what you get with Coolbook - perhaps they lowered the voltage that gets sent to the processors?
Kirk
5.
Benny | April 15, 2008 at 5:18 am
I’m still curious as to what is the real cause of the problem though because I still feel this must mean that something in essence is wrong with your Macbook Air - and all the others with the same issue. I’ve got a Macbook Air and have not had the heating issue at all, nor have I in fact ever heard the fans rev up !
Mostly I run light applications but as a test last weekend I watched a full 45 minute episode of Lost over the wifi network (because I had the file on my timecapsule) and played via the S-Video adapter to my TV. No problemo.
6.
Glenn | April 24, 2008 at 6:48 pm
Benny, have you tried hooking your MBA up to a Cinema Display? That is the ONLY time I experience core shutdown myself. If you never attach an external monitor or other peripherals, you should be OK!
7.
Pedram | April 26, 2008 at 10:41 pm
I also had a lot of similar problems. My primary symptom was that the trackpad would stop responding properly and the arrow kept skipping around the screen intermittently. I observed this behavior mostly when I hooked up my MBA to my HDTV to watch iTunes movies. In noticed that the machine got very hot each time the problem occured.
I later realized that the same problem happened if my machine was close to other electric appliances. But if I had it on a wood or grounded surface the problem went away. There is a tile counter at my home where every time I set my MBA on it the trackpad stops responding. Then I pick it up and hold it in my hands and the problem goes away.
I convinced Apple to replace my MBA with a new one. I ended up with the same exact behavior with the new machine. When I read this article and used Coolbook as suggested, my problem was dramatically reduced in frequency. I applied the firmware update and thought perhaps it would fix my problem. I tried turning off Coolbook to see if the firmware update solved my problem but it didn’t. I turned Coolbook back on and the problem went away for the most part. I do still have some problems when hooking up to my HDTV. But it is more manageable than before. I love my MBA had it been not been for this particular problem.
8.
Justin Shattuck | May 5, 2008 at 4:03 pm
I currently have my AIR on a 24″ cinema display and it has been performing as you mention in your post since the new firmware update.
Straight out of booting-up it hangs. And apple’s response, “its user specific.”
Going to try coolbook.
9.
Justin Shattuck | May 5, 2008 at 4:04 pm
I’ve been on hold for a air product specialist for about a hour now and its still unstable. I am so frustrated; about to go back to MBP
10.
Justin Shattuck | May 5, 2008 at 4:09 pm
Great, it won’t install the coolbook driver; ideas now?
11.
Lorent Duce | May 10, 2008 at 4:42 am
My problem is when I run XP through Bootcamp. The videos I play freeze up and the computer become useless.
All of my college classes are video streamed so this makes the problem even more irritating. Is there any way to use something like Coolbook when using Windows.
Thanks
12.
Pedram | May 14, 2008 at 4:39 am
You probably downloaded the old version of Coolbook. The website is confusing. Use latest version (I believe it’s 2.9).