Glossary
Memory pressure
How hard macOS is working to keep enough memory available for your apps.
What it is
Memory pressure combines how much memory is free, how much macOS is compressing, and how much it is swapping to disk into one reading. It is the best single answer to “does this Mac have enough memory right now?”
Low free memory on its own is normal. macOS fills spare memory with cached files and gives it back when apps need it. Pressure rises only when macOS has to work to find room: compressing more and writing to swap.
Why it matters
Rising pressure is the most common reason a Mac with plenty of CPU headroom still feels slow. Apple's guide puts it simply: green means memory is used efficiently, yellow means the Mac might eventually need more, red means it needs more.
In Activity Monitor
The Memory Pressure graph at the bottom of the Memory tab, coloured green, yellow or red.
In iKnowMyMac
The Memory tab shows the pressure state (normal, warn or critical) with swap and the memory breakdown. Diagnosis looks for pressure together with swap growth and names the apps that grew.
memory_pressurePrints the system-wide free memory percentage and paging statistics.
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