Glossary
Mac performance, in plain English
23 terms you'll meet in Activity Monitor and iKnowMyMac: what each means, why it matters, and where to find it.
Memory
- Memory pressureHow hard macOS is working to keep enough memory available for your apps.
- App memoryThe memory used by apps and their processes, as opposed to the system or file caches.
- Wired memoryMemory the system needs to run, which can't be compressed, swapped or given to apps.
- Compressed memoryMemory that macOS has compressed in RAM to make room, instead of writing it to disk.
- Cached filesFile data macOS keeps in otherwise unused memory so it can open it again quickly.
- SwapSpace on your startup disk that macOS uses as extra memory when RAM runs short.
- Physical footprintThe memory a process is responsible for, including its compressed memory.
CPU and heat
- CPU load averageThe average number of threads running or waiting to run, over the last 1, 5 and 15 minutes.
- Performance and efficiency coresApple silicon's two kinds of CPU core: fast performance cores and low-power efficiency cores.
- Thermal statemacOS's rating of how hot the Mac is: nominal, fair, serious or critical.
- kernel_taskThe macOS kernel, shown as a process. High CPU usually means it is managing heat.
Energy and sleep
Processes
- Process vs appAn app is what you open. A process is a running program. One app often runs many processes.
- launchdThe first process macOS starts. It launches and manages almost every other process.
- WindowServerThe system process that draws your windows and puts them on screen.
- Listening portA network port a process has opened to accept connections, like a dev server on port 3000.
More
- Purgeable spaceDisk space macOS counts as available because it can reclaim it on its own when needed.
- Full Disk AccessA macOS privacy permission that lets an app read folders other apps and the system keep private.
- Bundle identifierAn app's unique reverse-domain ID, such as com.apple.Safari, used to name the files it keeps.
- SSD wearHow much of an SSD's rated write endurance has been used, reported by the drive itself.
- Signal-to-noise ratioHow far a Wi-Fi signal stands above the background noise, in decibels. Higher is better.
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