What is System Data on a Mac, and how do you shrink it?

System Data on a Mac is the slice of Storage settings that collects everything macOS cannot place in a named category. It often reaches tens of gigabytes, and the pane has no button to look inside. This page covers what Apple says it contains, what inflates it, why tools disagree about its size, and how to shrink it safely on macOS 27, macOS 26 Tahoe and macOS 15 Sequoia (same behavior on all three).

What Apple says System Data is

Find it in Apple menu > System Settings > General > Storage. Apple's Mac User Guide says it "contains files that don't fall into the categories listed here", and "primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources." The guide also lists temporary files, fonts, app support files and plug-ins.

Two more lines from Apple matter:

• "You can't manage the contents of this category." There is no Info button next to System Data.
• It "varies in size depending on the current state of your Mac." It grows and shrinks on its own.

Apple's Free up storage space on Mac article calls it "System Data (or Other)"; older macOS showed it as Other. It is not the macOS category, which covers system apps such as Mail, Terminal and Calculator.

What typically inflates it

Apple publishes no breakdown. Going by its definition and where macOS keeps things, these are the usual contributors:

iPhone and iPad backups show under iOS Files. Mail and Messages, including attachments, have their own categories.

Time Machine local snapshots

According to Apple, Time Machine saves a local snapshot about hourly and keeps it for 24 hours. It also keeps one of your last successful backup until space is needed, and saves one before a macOS update. Snapshots hold data you have since deleted, so deleting a big file can free nothing until the snapshot goes. Apple does not name snapshots in its definition, but they are a common cause of sudden growth.

App data and caches

Apps store data in Application Support. Sandboxed apps keep their whole private home in Containers, and apps from one developer share Group Containers, which macOS creates and never removes. Caches hold data that, in Apple's developer documentation, "can be regenerated as needed".

Developer tools

Xcode build data, simulators, Android SDKs, Docker Desktop's disk image and package manager caches fit no other category, so they land here. On a developer Mac they are often the biggest part. Docker's disk image reports its maximum size, so Finder shows more than it really uses; see Docker.raw on a Mac.

Why Settings, Finder and Disk Utility disagree

It is normal for Storage settings, Finder and Disk Utility to show different free space. The reasons:

• Purgeable space. Disk Utility says available space "can include both free space and 'purgeable space'", which macOS frees when needed. You cannot remove it by hand.
• Snapshots count as available. Apple: "Your Mac counts the space used by snapshots as available storage." The blocks stay in use until macOS removes the snapshot.
• Shared APFS space. All volumes in an APFS container share its free space, so one volume's available space depends on the others.
• Sparse files and clones. Some files report more size than the disk space they use. Docker's disk image is the usual example.
• Units. Finder and Storage settings use decimal units (1 GB = 1,000,000,000 bytes). du -h and df -h use powers of 1024, so their numbers look about 7% smaller.
• Timing. The Storage pane keeps calculating after you open it, and independent testing on macOS 26 found snapshot purging can take many minutes. Waiting and checking again is a real step.

How to look inside System Data safely

Storage settings has no Info button for System Data, so look at the folders that feed it. Start with your home Library.

1. In Finder, choose Go > Go to Folder and type ~/Library.
2. Choose View > as List, then View > Show View Options and turn on Calculate all sizes.
3. Click the Size column to sort and open the largest folders.

Or in Terminal, read-only:

du -xh -d 1 ~/Library | sort -h
du -xh -d 1 ~/Library/Application\ Support | sort -h
tmutil listlocalsnapshots /
sysctl vm.swapusage

These change nothing. They show folder sizes, the local snapshots on your startup disk, and swap in use.

How to shrink System Data, step by step

1. Empty the Trash. Deleted files take space until then.
2. Deal with local snapshots. Apple's method: System Settings > General > Time Machine, turn off automatic backups, wait a few minutes, turn them back on. To delete one snapshot, run tmutil listlocalsnapshotdates /, then tmutil deletelocalsnapshots with that date (add sudo on a permissions error). Do this only with a real backup elsewhere.
3. Clear caches one app at a time. Quit the app, then move its folder in ~/Library/Caches to the Trash. It is rebuilt on next launch.
4. Use each developer tool's own cleanup. See Clear Xcode DerivedData, Delete iOS simulators and Docker.raw on a Mac.
5. Uninstall unused apps, then their leftovers. Use the app's uninstaller if it has one, then check Application Support, Containers and Group Containers for its folders.
6. Wait, then check again. Snapshot purging and the pane's totals both lag.

Apple also notes that starting up in safe mode clears certain system caches, and a restart recreates swap files. Neither is a lasting fix. For the rest of your disk, see How to free up disk space on a Mac.

What never to delete

System Integrity Protection lets only Apple-signed installers and updates change /System, /usr, /bin, /sbin and /var. Guides that say to run sudo rm -rf there, or on the Spotlight index, ask you to bypass the Trash on files you cannot get back.

Questions

Is System Data the same as Other on a Mac?

Yes. Apple refers to it as System Data (or Other). Older versions of macOS used the name Other.

Can I delete System Data on a Mac?

Not as a category. Apple says you cannot manage its contents in Storage settings. You reduce it by removing what feeds it, such as snapshots, caches and app or developer data.

Why is my System Data so large?

The usual causes are Time Machine local snapshots, app support data and containers in ~/Library, caches, and developer tools such as Xcode, simulators and Docker. Apple notes the category varies in size with the current state of your Mac.

Does System Data include Time Machine snapshots?

Apple does not list snapshots in its definition of System Data, but local snapshots are system-managed and a common reason for sudden growth. Apple says macOS deletes them as they age or as space is needed.

Does System Data include iPhone backups?

Normally no. Storage settings shows iPhone and iPad backups under iOS Files. They live in ~/Library/Application Support/MobileSync/Backup/.

Why does Finder show more free space than Storage settings?

Finder and Disk Utility count purgeable space, including Time Machine snapshots, as available, even though those files still exist until macOS removes them.

Why does System Data shrink on its own?

Local snapshots expire after 24 hours, and macOS removes purgeable files when space is needed. The Storage pane also keeps recalculating for a while after you open it.

Will deleting System Data break my Mac?

Deleting inside folders protected by System Integrity Protection is blocked or breaks startup, and deleting an app's Containers or Application Support folder deletes that app's data. App caches are designed to be rebuilt and are safe to clear.

How do I clear System Data without third-party software?

Empty the Trash, toggle Time Machine automatic backups off and on, clear one app's cache at a time, delete old iPhone backups with Manage Backups, and remove developer build data with each tool's own command.