Utilities: Your OS X Toolbox
The Utilities folder (inside your Applications folder) is home to a couple of dozen tools for monitoring, tuning, tweaking, and troubleshooting your Mac and its components.
The truth is, you’re likely to use only about six of these utilities. The rest are specialized gizmos primarily of interest to network administrators or Unix geeks who are obsessed with knowing what kind of computer-code gibberish is going on behind the scenes.
Activity Monitor is designed to let the technologically savvy Mac fan see how much of the Mac’s available power is being tapped at any given moment.
The Processes table
Even when you’re running only a program or two on your Mac, dozens of computational tasks (processes) are going on in the background. The top half of the dialog box, which looks like a table, shows you all the different processes—visible and invisible—that your Mac is handling at the moment.
Check out how many items appear in the Process list, even when you’re just staring at the desktop. It’s awesome to see how busy your Mac is! Some are recognizable programs (such as Finder), while others are background system-level operations you don’t normally see. For each item, you can see the percentage of the CPU being used, who’s using it (either your account name, someone else’s, or root, meaning the Mac itself), whether or not it’s been written as a 64-bit app, and how much memory it’s using.
Or use the View menu above the list to see views like these: