If your Mac is running slow or hot, use Activity Monitor to see what your computer is doing ‘under the hood’:
1. Launch Activity Monitor (it’s in the Applications > Utilities folder). You can also choose “Utilities” from the Go menu in the Finder or use Spotlight (Command – Spacebar) to search for and launch Activity Monitor.
2. Upon first launch choose “All Processes” from the View menu. This will show all software processes running on the computer.
3. Click the “CPU” tab at the top.
5. Note any applications which are unexpectedly using more than 15-30% CPU for more than a few seconds. Apps and processes will rise and fall in the list, as they kick in, do some work and then fall off in CPU utilization.
In the screenshot above, you can see the Photos application is using nearly 80% of my CPU – this is during a large import/merge in the Photos app, so the high CPU utilization makes sense.
6. Search Google for apps/processes you don’t recognize. This can help diagnose what might be causing a machine to run slowly (or warm, if the CPU is working hard).
7. Quit unused applications and/or any which are taking up large amounts of CPU cycles.
8. To quit/force-quit a stuck/hung/frozen app or process, select it in the list and click the “X” icon at the upper left.