Open System Settings > General > Storage on a Mac and you will see a grey segment labelled System Data. On some Macs it is a few gigabytes. On others it is 50, 100 or more. Because you cannot click into it and manage it like other categories, it can feel like a mystery.
What System Data actually contains
Apple describes System Data as files that do not belong in the other categories. In practice, that typically includes:
- Caches created by macOS and apps.
- Logs and diagnostic reports.
- Virtual memory (swap) files that macOS uses when physical memory is full.
- Temporary files created while apps run or updates install.
- Time Machine local snapshots, kept on your startup disk between backups.
- App support files, plug-ins, fonts and other runtime resources.
Some of this is essential and some is disposable, which is why macOS does not let you delete it wholesale.
Why it keeps changing
System Data rises and falls on its own. Swap files grow when you use a lot of memory and shrink after a restart. Local snapshots appear and are removed as Time Machine runs. Caches grow as you use apps. A large System Data number is not necessarily a problem unless it keeps growing or your disk is nearly full.
Safe ways to reduce System Data
1. Restart your Mac
A restart clears swap files and many temporary files. If you have not restarted for weeks, this alone can recover several gigabytes. Check Storage again a few minutes after restarting.
2. Install macOS updates
Choose System Settings > General > Software Update. Finishing a pending update removes the downloaded update files, and updates sometimes fix bugs that cause runaway logs or caches.
3. Clear large app caches
Browsers, video editors, music apps, messaging apps and developer tools can keep very large caches. Many of them are counted in System Data. Use each app's own setting to clear its cache where possible, or follow our guide to clearing the cache on a Mac.
4. Check Time Machine local snapshots
If you use Time Machine, macOS keeps local snapshots on your startup disk so you can restore files even when your backup drive is not connected. These are counted in System Data on some versions of macOS.
To see them, open Terminal and run:
tmutil listlocalsnapshots /
This command only lists snapshots; it does not change anything. macOS automatically deletes local snapshots when it needs space, and older snapshots are removed after a successful backup to your Time Machine drive. Connecting your backup drive and letting a backup complete is the simplest way to let macOS tidy them up.
5. Remove old device backups and installers
Old iPhone and iPad backups are usually shown under iOS Files, but on some Macs related files can inflate System Data. Remove backups you no longer need in Storage > iOS Files or via Finder. See deleting old iPhone backups on a Mac.
Also check your Applications folder for an old Install macOS app. These installers are large and can be deleted once you have upgraded.
6. Check developer tools
If you use Xcode, simulators, Docker or package managers, a lot of their storage can appear as System Data or Developer. Xcode's DerivedData and simulator runtimes are common culprits. See clearing Xcode DerivedData and simulators.
What not to do
- Do not delete folders in
/System,/private/varor/Librarybecause a forum post said they are "junk". macOS needs many of them, and removing the wrong ones can stop your Mac from starting up. - Do not disable System Integrity Protection to delete files.
- Be careful with Terminal commands that delete snapshots or caches. If you do not know exactly what a command removes, do not run it.
When to consider a reinstall
If System Data stays enormous after all of the above, a clean reinstall of macOS from a backup can reset it, but this is time-consuming and rarely necessary. Most of the time, a restart, updates and clearing a few large caches bring it back to a sensible size.
Frequently asked questions
Why is System Data so large on my Mac?
Usually because of large app caches, swap files from heavy memory use, Time Machine local snapshots, or leftover update files. A restart, installing updates and clearing large app caches often reduce it considerably.
Can I delete System Data?
Not directly from Storage settings, and you should not delete system folders manually. Reduce it indirectly by restarting, updating macOS, clearing app caches and removing old backups and installers.
Is System Data the same as Other storage?
Yes. Older versions of macOS called this category Other. Newer versions split some of it into categories like iOS Files and Developer, and label the remainder System Data.
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