Introduction Link to heading Imagine you opened Activity Monitor to check how much memory your application consumes. But wait, which number should you actually look at? Suppose there’s “Memory” showing 800 MB, and “Real Memory” showing 1 GB. What’s the difference? Note Activity Monitor doesn’t display those two readings by default. To show them, you need to right-click on a table header and select them. This exact scenario happened to me more times than I’d like to admit. As someone who keeps Activity Monitor perpetually open, I found myself constantly puzzled by these two memory metrics. Coming from a Linux background where RSS (Resident Set Size) tells a straightforward story, macOS’s dual memory reporting felt like reading tea leaves.