I've got the Early-2015 13" MacBook Pro (2.7 GHz i5) and whilst I was building Smart Previews for all my 1600+ photos in Lightroom 5 I noticed that the fan had come on (unusually) and that the laptop was starting to get rather hot.

When I had a look at Activity Monitor, I saw that Lightroom was using around 300% CPU. Fair enough, I'm sure it's an intensive process. However, I also saw the usage for Lightroom jump higher than 400% on several occasions (usually up to around 410%).

I understand how my CPU is Hyper-Threaded so that it has 4 cores/400% CPU available, but how could it possibly use more than that (bearing in mind several other processes were running as well)?

Cheers, Dan

  • What does top tell you?
    – bot47
    Feb 8, 2016 at 15:21

2 Answers 2


If you look here, you have 2 cores that can execute 2 threads each with turbo boost. So I would assume 400% is your maximum. Seems likely that Adobe maxed out one CPU completely, and the other CPU was running the OS and other tasks.

The additional usage may be because your 2.7 ghz CPU was turbo boosted to 3.1 ghz at the time.

Also, within Activity Monitor, you can choose Window -> CPU History, and it will break down everything. For example on my 6 core Xeon, I have 12 graphs.


This system also supports "Turbo Boost 2.0" -- which "automatically increases the speed of the active cores" to improve performance when needed (up to 3.1 GHz for this model) -- and "Hyper Threading" -- which allows the system to recognize four total "cores" or "threads" (two real and two virtual).

(as found on this page)

The turbo boost lets your processor go beyond the 100% threshold for intensive tasks

  • But my CPU is only dual core? It should only have 4 logical processors, surely?
    – Dan Grove
    Feb 5, 2016 at 16:03
  • I edited my answer Feb 8, 2016 at 9:30
  • If turbo boost is started, shouldn't it stay at 100% or even drop BELOW 100%? The CPU increases its potential while the task stays the same...
    – bot47
    Feb 8, 2016 at 15:22

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