The 24 inch iMac with the M4 chip is a fast desktop, and a slow one has a cause that Apple's page for a Mac that runs slowly can find. Open Activity Monitor and watch the CPU and Memory tabs for an app using a large share, and read the Memory Pressure graph: green is fine, yellow is working hard, and red means the iMac is short of memory and swapping to the drive, which makes everything slow. The iMac's memory is built into the chip and cannot be upgraded, so a 16 GB iMac with a heavy workload of browsers, design apps and video calls can run short; closing apps frees it.
The checks in more detail
Login items that start with the Mac slow the first minutes after a restart, and System Settings, General, Login Items lists them. A drive nearly full slows macOS because it needs free space for swap and caches, so keep ten to twenty percent free. A Mac that has been on for weeks without a restart is sluggish, and a restart is free. After a macOS update, Spotlight and Photos index in the background for a day, so the iMac feels slow until they finish.
Check the apps you use: a browser extension, a security tool or a cloud sync client may be the culprit. Quit the suspect and watch whether the iMac speeds up. Try Safe Mode by holding the power button at start-up and pressing Shift with the disk selected: if the iMac runs normally there, a login item or extension is at fault. Make sure macOS is current and apps are updated. If the iMac is slow only on the network, the problem is the Wi-Fi or the internet, not the Mac. External drives that are failing can freeze apps that touch them, so unplug drives to test.
If the iMac stays slow with green memory pressure and a clean Safe Mode, run Apple Diagnostics and contact Apple Support. For creative work on the iMac, check where your files live: a project on a slow external drive or a network share makes the whole app feel slow, even though the iMac is fast. Move the active project to the internal drive or to a fast SSD over Thunderbolt, and keep the cache folders of your apps on the internal drive. That change often makes more difference than any macOS setting.
Differential
Likely causes of “Apple iMac 24-inch (M4) is running very slowly”, and how to tell them apart
- 1
Memory pressure in the red
What separates it Everything stutters
How to confirm Close apps; memory cannot be upgraded
- 2
A process using the CPU
What separates it One app tops Activity Monitor
How to confirm Quit or update it
- 3
A full drive
What separates it Slow saves and beach balls
How to confirm Free ten to twenty percent
- 4
Indexing after an update
What separates it Slow for a day
How to confirm Leave it running
- 5
A failing external drive
What separates it Apps freeze that touch it
How to confirm Unplug to test
Before you touch a setting
Record this first — changing settings destroys the evidence
- The Memory Pressure color
- The top process
- The free storage
- Whether Safe Mode is fast
Try in this order
0 of 6 completedOpen Activity Monitor
ReversibleCPU and Memory tabs.
Read Memory Pressure
ReversibleGreen, yellow or red.
Quit heavy apps
ReversibleThen retest.
Check Login Items
ReversibleSystem Settings, General.
Free storage
ReversibleTen to twenty percent.
Try Safe Mode
ReversibleTo rule out login items.
Model-specific
What is true of this model and not of its siblings
- Unified memory
- It cannot be upgraded.
- Safe Mode
- It disables login items.
Stop boundary
When this stops being a self-service repair
- !If it is slow in Safe Mode with green memory pressure, contact Apple Support
- !If a drive reports errors, back up and ask Apple
- !Run Apple Diagnostics
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why is my iMac slow?+
Memory pressure or a busy process.
Can I add memory?+
No, it is built into the chip.
What does red memory pressure mean?+
The iMac is short of memory.
Do updates slow it?+
For a day.