AnandTech has a instructions1 on how you can check the Turbo Ratios for the Mac's CPU. Since they are logged, the information is very easy to find.
In Mountain Lion you can do this the following way:
- Open the
system.logon the left side.
- Search for entries containing
What you'll find is something like this:
Dec 16 20:11:47 localhost kernel: AppleIntelCPUPowerManagement: Turbo Ratios 0035
And this means:
The line above lists turbo ratios as 0035. The four digit number is the turbo ratio for the active cores (4C/3C/2C/1C). Depending on the active cores, the clock speed can vary. Each number is hexadecimal.
The first two numbers are 0s because the CPU doesn't have more than two cores and thus doesn't support any turbo ratios when 4 or 3 cores are active (2012 Macbook Air, i5-3427U). The third number tells us the maximum turbo boost with two cores active: 3. That's 3 bins, where each bin is 100MHz, or 300MHz above the stock 1.8GHz operating frequency (2.1GHz).
The fourth number gives us max turbo when only a single core is active: 5. Five bins is 500MHz, which on top of the 1.8GHz base frequency gives us 2.3GHz.
(Edited text from AnandTech to fit my CPU.)
This raises the obvious question: Why is my Mac's CPU throttled?
I wish I were able to use the MSR tools to get more information about the clock speeds, but for them to work I need to boot in 32-bit kernel mode which is not available in Mountain Lion anymore.
MacCPUID4 is an official tool by Intel which you can use to calculate the current CPU clock. The current version 2.1 has been released on the 10/31/2012 but still seems buggy. No matter how I stress my CPU, it always calculates that the clock is at a constant 2.3 GHz.