Why is my Mac's CPU throttled? (Turbo Boost Ratio)

So, I ran some Cinebench R11.5 benchmarks to get more information about the single threaded performance of my i5-3427U¹ (1.8-2.8 GHz) CPU:

1 thread → 1.10

I also contacted the author of the linked article by AnandTech - @anandshimpi². Anand Lal Shimpi was so kind to send me a benchark chart which compared the single threaded performance of the 2011 13" Macbook Airs with the 2012 13" Macbook Airs using Cinebench R11.5.

Into this picture, I have added information about the maximum single threaded CPU clocks along with a comparison of the measured performance such as Anand Lal Shimpi has suggested.

^{[image source]}

In this info graphic I am comparing specifically:

• 2011 13" Macbook Air, i5-2557M 1.7GHz/2.4GHz/2.7GHz
• 2012 13" Macbook Air, i5-3427U 1.8GHz/2.6GHz/2.8GHz

As you can see, the single threaded clock of the 2012 model is 3.7% increased in turbo boost mode.

However, the benchmark score saw a 9.9% increase which is not simply due to the higher clock, but also due to the more efficient Ivy Bridge architecture which is about 5-15% faster³ than Sandy Bridge.

In sum, the benchmark scores are as expected whereas the Turbo Ratios log entries are not. Anand Lal Shimpi had "figured it was a bug, submitted it to Apple back in July"⁴.