The macOS Activity Monitor – memory usage


Many of us use a terminal and command-line tools to check memory usage of the Mac.

The output of “top” utility in terminal

While console utilities are bullet-proof and provide enormous details, “Activity Monitor” is not falling far behind in terms of its usability. Let’s talk about the “memory” tab.

Press Alt + Space and type “Activity Monitor” to run the app

“Physical Memory” – obviously, tells about the amount of the physical RAM installed on a given machine.

“Memory Used” – the amount of memory currently utilized by apps and OS. As you see, it expands to the right showing a breakdown by usage.

  • “App Memory” – how much memory do the user-space programs use. It includes tools and services started by the user, such as browsers, games, editors, etc.
  • “Wired Memory” stands for the memory that the OS needs to operate. This memory is not accessible by user-space tools and always dedicated to OS only.
  • “Compressed” is the memory that was constricted by the OS when there are not enough resources for other apps. Every application on the picture above has this column. In the provided example, the system did not compress any memory for any of the apps.

“Caches Files” is memory with cached files for better performance. For example, recently you accessed some huge doc file. Next time when you open it, you see much faster loading time because of the caching.

“Swap Used” is the amount of hard drive (disk space) used in addition to RAM. When the OS has no memory to run another app, it unloads the less frequently used data to the filesystem.

Small “pro” tip. If you need to see other columns for additional information, click on “View” as shown on the screenshot below.