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

What is in System Data?

Apple describes System Data (called "Other" in older versions of macOS) as a general category for files that don't fit a more specific category. In practice it is whatever is left after macOS adds up the others. Common contents:

• Caches that apps and macOS create to work faster, mostly in ~/Library/Caches.
• Logs and temporary files written by apps and the system.
• Local Time Machine snapshots, which macOS keeps on your Mac between backups.
• Virtual memory (swap) and sleep files, which macOS manages itself.
• App support data in ~/Library/Application Support, such as downloaded AI models, virtual machine disks and game data.

Storage settings has no details button for System Data, which is why it can feel like a mystery. The steps below go through the usual causes one at a time.

Why does System Data keep changing size?

Much of it is temporary. Swap grows when memory is tight and shrinks after a restart; snapshots are added and removed around Time Machine backups; caches grow as you use apps. A large jump is often a snapshot or an app's cache, and it may disappear on its own within a day.

How to reduce System Data safely

1. Restart your Mac

A restart clears swap files and many temporary files. It is the easiest first step and costs nothing.

2. Check for local Time Machine snapshots

If you use Time Machine, macOS keeps local snapshots on your disk and removes them when space is needed. To see them, open Terminal and run:

tmutil listlocalsnapshots /

You can also see them in Disk Utility with View › Show APFS Snapshots. macOS deletes local snapshots automatically, so you rarely need to remove them yourself. If you do, use the date exactly as shown in the list, for example:

sudo tmutil deletelocalsnapshots 2026-10-22-101530

Remove only snapshots you don't need. sudo asks for your Mac password.

3. Clear caches for apps you no longer use

Caches are rebuilt by apps when needed, so removing them is low risk, but the space comes back as you keep using the app. Focus on large caches from apps you have stopped using. Our guide is it safe to delete cache files on a Mac? explains how.

4. Look inside Application Support

In Finder, choose Go › Go to Folder and enter ~/Library/Application Support. Switch to list view and turn on View › Show View Options › Calculate all sizes. Large folders often belong to virtual machines, AI tools, games or apps you have already deleted. Remove data only for apps you no longer use, because this folder also holds settings and documents.

5. Remove developer data

If you use Xcode or other developer tools, build data and simulators can be large. On newer versions of macOS some of this appears under the Developer category instead. See how to clear Xcode DerivedData safely.

What not to do

• Don't delete folders in /System, /private/var or /Library that you don't recognise.
• Don't turn off System Integrity Protection to "clean" system files.
• Don't reinstall macOS just to shrink System Data. It is rarely needed.

Where TheCleanDisk helps

TheCleanDisk breaks down what is hiding in System Data, such as caches, logs and developer data, and explains each item before you choose. Only things apps rebuild on their own are pre-selected, and every clean can be undone for 7 days. The space is fully freed when quarantine empties, or sooner if you empty it yourself. It is coming soon to the Mac App Store.