Wednesday
Apr022008
MacBook Air Core Shutdown
Wednesday, April 2, 2008 at 2:33PM 
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.
Reader Comments (9)
[...] not mentioned by name, this warning is an obvious reference to Coolbook; a third party app that I covered in an earlier post that lowers the voltage fed to the [...]
Apple have finally released a fix for the core shutdown issues plaguing MacBook Air owners. The support notes warns third party apps that alter the voltage or characteristics of the CPU are incompatible with the patch and that they should be removed before the update is applied. Although not mentioned by name, this warning is an obvious reference to Coolbook; a third party app that I covered in an earlier post that lowers the voltage fed to the CPU.
I have been running a newly patched MacBook Air for a few hours now. During that time I have had three flash videos running simultaneously along with Activity Monitor. I have yet to see a CPU core shutdown leading me to believe, that after a six month wait, the Apple update resolves this issue once and for all.
so.... i downloaded the patch yesterday 28 Aug 2008. I turned of coolbook as apple recommended. I tested my mba for hours. With external temperature 30 C, 2 youtubes, google earth, itunes and activity monitor the cpu temp is reaching never more than 70 C. With just itunes, wifi on, and 1 window of safari open, the temp never drops 53 C and the fan spins at 6155-6204 rpm. There is no core shutdown until now.
But......there is one more thing.....
In high temperatures and when many apps are open, or more correctly before the cpu shows 52-55 there is a slight slow down in the laptops performance (not freezing, i can still work normally). Reactions like that reminds the performance of my mba (sata, 1,6), before i use cool book and when i had 1 core shut down. With cool book there was no slow down at all, but the temp was very high always (60-65 C), and most of the time it was impossible to leave the mba in bear legs, and it was so hot that i could not touch it.
Anyway i do not know if the issue is fix for sure by apple with the patch......
My MacBook Air did the same thing, so I took it to the Apple store (still under warranty) and showed them. They sent it to a repair station in Texas, and they replaced the motherboard and installed a cooling upgrade, all for free. It now works much better, and I've not had a core shutdown since.
I have installed Coolbook as my MBA was running extremely hot. I live in humid state as well which didnt help anything. I have since installed Coolbook and SmcFanControl and my machine is running 'much' better. The CPU temp is much lower than usual. The fan speed is still alot higher but thats because I have SmcFanControl running as well. Go MBA!! I do love the machine even though it needs help like this at times!
Love the advice. Thank you.
[...] Langsom MacBook Air Jeg har haft problemer med at min MacBook Air blev langsom sidst på eftermiddagen. Selvom jeg lukkede programmerne ned så brugte den systemressourcer der var helt abnorme på ca. 80% og den var frygtelig langsom og hang i programmerne. Jeg har surfet lidt og fundet programmet coolbook – se www.coolbook.se da problemet åbenbart – hvad jeg kunne læse mig til – er at computeren lukkede en af de to CPU’er ned ved kraftig belastning og når den blev lidt varm, hvilket bl.a. sker når der er tilstluttet ekstraskærm, mus m.v.. Jeg har nu efter nogle anbefalinger leget lidt med programmet og det ser ud til at virke – se evt. mere på Plasmablog [...]
Coolbook cured my mac air shutdown/overheating problem as well. No more overheating while I watch videos.
Did you notice a significant decrease in speed? I may mod mine as i have found mine shuts down, especially after the kids have spent a while watching youtube as you found!