Figure out if you Mac just needs to catch a breath or needs a hard restart by watching the Activity Monitor Dock icon.
Force quit programs from the process list.
Spy on which programs are using your Mac's power and close the ones that are hogging them.
Check out if you are using all your RAM or if you need more.
3 Great Uses for Activity MonitorCategories: Home, Mastering the Mac, Getting Help
Ah, Activity Viewer, the unsung, yet most used utility in the Utilities folder. You are the Cinderella of my Apps. I "Hide" you upon start-up, but you are the first one I turn to when I need help. At least you are at the top of the Utilities list when I peek at it in Column View.
To the new Mac user, the programs in the Utilities folder can seem opaque and dangerous, and to some extent that's true. But start exploring with Activity Viewer and System Profiler. These give you tons of information about your new Mac and how it's running.
So what are my top 3 ways to use Activity Viewer? Let's start with the most used.
Use the Dock icon to monitor CPU History
I have Activity Viewer launch and hide at start-up so it is always open and operating, but not getting in my way. I also set the Dock icon to show CPU History. What this gives you is a real time graph about how hard your CPUs are working sitting in your Dock. (The CPU is your Mac's brain.)
Why would you want this? Because it gives you a clue to what is happening when your Mac's responsiveness slows down or worse, when you get the Spinning Beach Ball of Death (SBBoD).
Let's say you are seeing the SBBoD. If your Activity Monitor Dock icon shows a lot of moving activity like this below, it just means that your Mac is crunching away and needs a few seconds to get caught up. That's normal.
Now, the worse signal it gives you is when the graph looks normal like below, but the graph is not moving. That's the sign that you are hosed. You Mac is locked up and it will probably not be responsive again. If it doesn't start moving again in a few seconds, you will probably need to do a hard restart. I hope you saved recently.
There are several ways to force an application to quit, and sometimes you need to use them all to take down the obstinate app. You can do that by selecting the errant program from the list in the main window of Activity Viewer. Usually the one you are looking for is in red type and has the words "not responding" next to the name. You can select it from the list and then click the Quit Process button in the upper left. I'm not sure if it's the most effective way to force quit a program, but it seems to work more often than right clicking the Dock icon or bringing up the Force Quit box from the Apple menu.
Spying on your programs
When viewing Activity Monitor, the main area shows the different applications and processes your Mac is currently running. I typically keep the Activity Monitor window displaying the System Memory tab since the CPU tab is redundant with that data showing in the Dock icon, and I show All Processes from the drop down menu in the tool bar. I then sort the list by clicking the %CPU column head so the list reorders itself in real time with the most CPU hogging programs on top. This tells me who is dominating my Mac and which app to quit if my Mac is getting bogged down.
By viewing the System Memory tab at the bottom, you can also determine if your Mac has sufficient RAM for your uses. Start using your Mac like normal and then view the pie chart in the lower right of the window. If you don't have a decent sized slice of green and blue combined, you might want to add more RAM.
Now, Activity Monitor can give you info on a dozens or even hundreds of bits of info about your Mac and there are probably key ones I haven't addressed. What uses for Activity Monitor do you find most valuable? Let us know in the Comments section below!