Sometimes, a single misbehaving app can slow your Mac to a crawl. If you’re not sure what’s slowing your Mac down, turn to Activity Monitor—a free app built into Lion—to identify (and terminate) the bad apple.

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Show Notes

Command-line pros may notice that Activity Monitor is essentially a friendlier interface for the top command.

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Show transcript

I’m staff writer Lex Friedman, and I’m going to show you how to identify and deal with apps that are slowing down your Mac.

Sometimes, our Macs behave badly. If your Mac is grinding to a halt, occasionally, a single misbehaving app is responsible—but it’s not always obvious which app that is. The good news is, you can turn to another application that came free with your Mac for help, one that lets you quickly identify—and severely punish—the misbehaving app in question.

Go to your Applications folder, and find the Utilities folder inside it. Here, I typed the letter ‘U’ in the Applications window to jump right to the Utilities folder I was after.

Inside the Utilities folder sits Activity Monitor. Double-click it to launch it as you would any other app.

Activity Monitor shows all the apps and processes that are currently running on your Mac. When trouble’s afoot, you generally want to find out which app is dominating your Mac’s processors. To do that, you want to sort Activity Monitor by the “%CPU” column—so click on it. You might have to click on it twice to ensure that processes using the most CPU are sorted at the top.

Now, things hop around a bit in Activity Monitor, and that’s normal; different apps and processes are always running on your Mac, and sometimes will need to use a bit of extra CPU processing power—so don’t worry about that. What we’re looking for is an app that’s misbehaving, one that’s gobbling up more than it s fair share of CPU, and for too long a time.

This isn’t an exact science. But if my Mac’s going too slow, and I see, say, iTunes is up there gobbling up 90 percent or more of my CPU, I’ll gladly shut the app down to see if that improves things in a hurry. To quit a process, click on it, and then click the Quit Process button. Then you choose whether to Quit or Force Quit it. Force Quitting is riskier, if it’s an app that has unsaved changes—like, say, a Word document. But most of the time, I choose Force Quit anyway. It ensures the process will get terminated immediately, and it’s more viscerally satisfying, too.

Now, one more important tip about Activity Monitor. Its Dock icon can be extremely useful. Sure, the default chart looks lovely, but you can turn the Dock icon into a live-updating chart that shows precisely what’s going on behind-the-scenes on your Mac, in real-time. Control-click, two-finger click, or right-click on the icon, and choose an option from the Dock Icon submenu. I like the Show CPU Usage option. If that bar fills up too much—say, beyond halfway—I know something troubling may be unduly burdening my Mac’s processors, and I can click to see if there’s a process or two that I ought to Force Quit With extreme prejudice.

So that’s Activity Monitor. If your Mac isn’t running right and you’re not ready to reboot the whole enchilada, it’s worth a look. Thanks for watching.

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