When your Mac slows down, guessing which app is responsible wastes time. Activity Monitor shows exactly what is running and how much of your Mac's resources each process is using.
Open Activity Monitor
Press Command-Space, type Activity Monitor, and press Return. You can also find it in Applications > Utilities.
Along the top are five tabs: CPU, Memory, Energy, Disk and Network. The list below shows every process: apps you opened, plus helpers and system processes.
To see only apps, choose View > My Processes or View > Windowed Processes.
CPU: what is keeping the processor busy
Click the % CPU column header to sort with the busiest processes at the top. A process can show more than 100% because it is using more than one processor core.
What to look for:
- An app using a lot of CPU while you are not using it. That often points to a stuck task, a runaway web page, or a sync that is working hard.
- Browsers: each tab or extension can appear as its own process, often called "Web Content" or "Helper (Renderer)". A single busy tab can slow everything down.
At the bottom of the window, System, User and Idle show how the processor's time is divided overall.
Memory: is your Mac running short?
The most useful part of this tab is the Memory Pressure graph at the bottom:
- Green: memory is being used efficiently. High "Memory Used" is normal, because macOS uses spare memory for caching.
- Yellow: your Mac is working harder to manage memory, compressing data and using swap.
- Red: your Mac needs more memory than it has, and is leaning heavily on the much slower disk.
If the graph is yellow or red, sort by the Memory column and quit the largest apps you do not need. Also note Swap Used. A large and growing swap figure means memory is regularly running out, and having little free disk space makes this worse. See fixing "Your system has run out of application memory".
Energy: what is draining the battery
On a MacBook, the Energy Impact column shows which apps use the most power right now, and 12 hr Power shows the last 12 hours. Apps with high energy impact also tend to make your Mac warmer and the fans louder.
Disk and Network
The Disk tab shows which processes are reading and writing most. Heavy disk activity from Spotlight indexing, backups or sync tools can make a Mac feel sluggish. The Network tab shows data sent and received, which helps spot unexpected uploads or downloads.
Common processes explained
| Process | What it is | What to do |
|---|---|---|
kernel_task |
The core of macOS. High CPU often means it is keeping the Mac cool by limiting other work | Check for heat and heavy apps; do not quit |
WindowServer |
Draws everything on screen | High when many windows, displays or animations; close windows or reduce motion |
mds, mds_stores, mdworker |
Spotlight indexing | Normal after updates or large file changes; let it finish |
photoanalysisd, mediaanalysisd |
Photos analysing your library for faces and search | Normal after importing many photos; finishes on its own |
bird, cloudd |
iCloud Drive syncing | Busy when lots of files are syncing |
backupd |
Time Machine backups | Runs during backups |
How to quit a process
Select the process and click the Stop (×) button in the toolbar, then choose Quit. If it does not respond, use Force Quit. Force quitting can lose unsaved work, so save first if you can.
Do not quit processes you do not recognise, especially ones owned by "root" or "_" users. Many are part of macOS, and quitting them can cause problems until you restart.
Frequently asked questions
What does memory pressure mean on a Mac?
Memory pressure shows how hard macOS is working to fit everything into memory. Green is healthy, yellow means it is compressing and swapping more, and red means your Mac needs more memory than it has.
Why is kernel_task using so much CPU?
macOS uses kernel_task to limit other processes when your Mac gets too warm. Check for apps using lots of CPU, keep vents clear, and let the Mac cool down.
Is it safe to quit processes in Activity Monitor?
It is safe to quit apps you opened. Avoid quitting processes you do not recognise, as many are part of macOS.
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