yes takes CPU usage to 99% Running yes &gt; /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?
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.