Activity Monitor memory explained: app, wired, compressed and cached
What App Memory, Wired, Compressed, Cached Files and Swap Used mean at the bottom of Activity Monitor's Memory tab, with real numbers from an 8 GB Mac.
What does Memory Used include?
App Memory (apps and processes), Wired Memory (held by the system and not movable) and Compressed (memory macOS has squeezed to fit more in).
What are Cached Files?
Files macOS keeps in memory because you used them recently. They are released instantly when an app needs the space, so they do not make the Mac run out.
Why is memory always nearly full?
Because unused memory is wasted memory: macOS fills it with caches and compressed pages. The graph, not the total, says whether it is a problem: memory pressure, compressed memory, wired memory.
Common questions
Is it bad if Mac memory used is high?
No. macOS fills memory on purpose; the pressure graph shows whether it is short.
What is Cached Files in Activity Monitor?
Recently used files kept in memory; macOS frees them instantly when apps need it.