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Quick Tip: Understanding Activity Monitor

The Mac’s Activity Monitor shows what is running on your Mac at any given time. This allows you to see how different programs and processes affect your Mac’s performance. You can find the app inside the Applications/Utilities folder. The app is broken up into five different tabs: CPU, Memory, Energy, Disk, and Network.


CPU shows how the processes are affecting the processor. If your fan is spinning on your Mac for no apparent reason, this is the section that you want to investigate. I find that the % CPU section is the most helpful. You can sort by % to see which app is eating up the most of the processor capacity.

CPU tab of Activity Monitor


The Memory section shows information about how your RAM is being used. As with the CPU tab, you can sort by many different options. Toward the bottom, there’s a box with Physical Memory, Memory Used, Virtual Memory and Swap Used. Physical memory is the amount of RAM your Mac actually has installed. Memory used is the amount currently being used at the current time. Virtual memory is the amount of memory-address space that is being allocated for memory mapping. Swap used is the space on your hard drive used by the Mac’s memory management process.

Memory tab of Activity Monitor


The Energy tab is extremely useful for laptop users. The impact tab is a measure of how a process is affecting energy consumption. Lower numbers are better on this tab. The average impact tab is a measure of the impact over the past 8 hours (or since startup if it’s been less than 8 hours). App nap is a relatively new feature to OS X. This section shows which apps support it. App nap-enabled apps consume very little energy when they aren’t in the foreground. The preventing sleep tab shows if an app is actually preventing the Mac from going to sleep on its normal schedule.

Energy tab of Activity Monitor


The Disk tab shows the amount of data that a process has read from and written back to your hard drive. It also shows if it’s a 32- or 64-bit process.


The Network tab shows information about how your Mac is uploading and downloading network data. If an app’s usage seems relatively high, you might want to investigate if an app is talking to the web server without your knowledge. Little Snitch is a helpful app to block apps from “phoning home” without your knowledge.

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