User, System, Nice, Idle
When looking through the OS X Activity Monitor, I saw that it breaks down the CPU usage into categories. I see a lot of people asking what these mean but I don’t see many good explanations so I’ll take my crack at it here.
- %user: This is the percentage of your available CPU time that is being spent on programs that you executed or were executed on your behalf or by other users on your system. They are programs such as iMovie or Firefox.
- %system: These are the processes used by OS X to run your hardware and draw the pretty graphics on your screen. These processes are usually higher priority and at a low level that is not touchable by regular users.
- %nice: These are programs that typically run in the background to do some maintenance task and have a high “nice number”. This means that they willingly give up CPU cycles for other processes of the same priority level. An example would be a distributed.net client.
- %idle: Duh