yes takes CPU usage to 99%

Question

Running yes > /dev/null takes my CPU usage to 99%.

The Macbook Air 2018 have a 2 core CPU (1.6 GHz Core i5 [I5-8210Y]). Why is the "% CPU" taken by this process so high?

What did you expect? It just dumps data into the void, so the process doesn’t have to wait for disk IO, display updates or similar. — nohillside, Mar 29 '19 at 11:01

score 7 · Accepted Answer · answered Mar 29 '19 at 11:01

It is because Activity Monitor displays CPU usage as a percentage of a single core. So 100% means that one core is fully occupied.

The percentage can thus be higher than 100% when a program utilizes multiple cores.

The “yes” program is designed to use only one core, and use it fully. Therefore the behavior you’re seeing is entirely normal.

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