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Last weekend, my Macbok Air suffered a heart attack and I ended up doing several hard shutdowns due to an unresponsive system. In the end I had to do a full system restoration.

Everything is working fine now except for one thing: The CPU is slow. Much slower.

CPU related computing is much slower than before, even though I can't tell for sure how much exactly. When running Ubuntu, I monitor the clock speed and see that all four cores are running constantly at 0.8 GHz. The same is true for OS X when using the Intel Power Gadget. It used to be 1.8GHz to 2.6GHz. (Macbook Air 5-2, i5-3427U)

enter image description here

$ sudo modprobe msr ; sudo turbostat
cor CPU    %c0  GHz 
         11.50 0.80 
  0   0  13.34 0.80 
  0   2   7.76 0.80 
  1   1  18.47 0.80 
  1   3   6.44 0.80 

Could this be a software related issue? What should I do then?

I guess you see that a hidden assumption is that the firmware is corrupted. This is why I tried to reinstall the latest firmware for my Mac from https://support.apple.com/kb/HT1237. But when I install that file I get the error: "This software is not supported on your system." Most probably because the latest firmware version is already installed.

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Using the Intel power gadget (above) shows your CPU running at low speed.

In normal case that would be fine if there is no load.

I have MBA with 1.8 GHz Intel Core i5 and runs at 0.85 at normal use, how ever it does spikes to 1.8 + under load.

Since the computer processing speed depends on more than one factor (CPU +SSD read/Write+RAM)...

I would say you (your mac) is a candidate for the Apple Hardware test.

UPDATE:

If you have faulty battery (as reported by your hardware test based) then your Mac will automatically limit the CPU speed to about 1/2 (as designed by Apple.)

So fix the battery and you good to go.

  • I have performed the extended Apple Hardware Test. It only reported about the faulty battery (which I new already). Everything else is fine. The CPU clock is constant no matter how I stress the CPU. – gentmatt Aug 13 '13 at 16:12

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