What Is System Data on Mac and How to Reduce It

System Data on Mac is a catch-all storage category that contains caches, logs, local snapshots, iOS device backups and application support files — everything macOS cannot classify as Documents, Apps or Photos. You cannot delete it directly, but you can shrink it by removing the files that feed it.

What System Data Actually Contains

• Caches — system and app caches in ~/Library/Caches
• Local snapshots — Time Machine snapshots stored on your startup disk
• iOS backups — old iPhone and iPad backups in ~/Library/Application Support/MobileSync
• App support files — data left behind by apps, including uninstalled ones
• Logs and temporary files — diagnostic reports and swap files

How to Reduce System Data

1. Clear Caches

App and system caches are the largest contributor for most users. Remove them with a Mac cleaner that previews what it deletes, or manually from ~/Library/Caches if you know what you are looking at. Our guide on cleaning Mac cache covers this step by step.

2. Delete Old iOS Backups

Open Finder → Go → Go to Folder and enter ~/Library/Application Support/MobileSync/Backup. Old device backups can each occupy tens of gigabytes.

3. Remove Local Snapshots

Time Machine keeps local snapshots when your backup disk is disconnected. List them with:

tmutil listlocalsnapshots /

They are removed automatically when space is needed, but you can delete them manually with tmutil deletelocalsnapshots.

4. Uninstall Apps Completely

Leftover support files from apps you deleted long ago still count as System Data. A Mac cleaner or dedicated uninstaller removes the app and its leftovers together.

When System Data Keeps Growing

If System Data grows back quickly after cleanup, something is actively writing it — commonly a misbehaving app cache or a backup loop. A storage analyzer such as Neatwise shows which folders grow over time, so you can find the source instead of cleaning blindly.