How does my dual core i5 in my MacBook Pro have more than 400% CPU usage? 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
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.