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

What System Data is

System Data (older versions of macOS called it "Other") is the catch-all category in the Storage overview: everything that isn't an app, a document, a photo or another category macOS recognizes. It typically includes:

• Caches — from macOS, browsers and apps, in ~/Library/Caches and /Library/Caches.
• Time Machine local snapshots — copies of recently changed files kept on the startup disk.
• Virtual machine and container disks — Docker, Parallels, UTM and similar store whole disks as single large files.
• Developer data — Xcode build products, simulators and device symbols.
• App support files — databases, downloaded models, game assets and more in ~/Library/Application Support.
• Logs and temporary files, and the files macOS uses for virtual memory and sleep in /System/Volumes/VM.

How to see what's inside

The Storage screen doesn't break System Data down, and much of it lives in folders Finder hides. A disk space analyzer shows it folder by folder:

1. Scan your startup disk with DiskGarden (free).
2. Look at Users → your name → Library: Caches, Application Support, Containers and Developer are where most user-side System Data sits.
3. Space that DiskGarden can't read without extra rights — other users' files, protected system folders, snapshots — shows up as a purple hidden space petal. Scan as administrator to map it.

How to reduce it safely

Restart, then wait a little

macOS clears many temporary files and purgeable data on its own, especially after a restart. Check Storage again afterwards before deleting anything by hand.

Time Machine local snapshots

macOS keeps local snapshots so you can restore recent files even when your backup disk isn't connected, and deletes them automatically when space runs low. To see them, open Terminal and run:

tmutil listlocalsnapshots /

To remove one, run sudo tmutil deletelocalsnapshots followed by its date (for example 2026-10-01-101500). Only do this if you need the space right away.

Caches

Quit the app, then delete its folder in ~/Library/Caches. Apps rebuild what they need, so this frees space but some of it comes back.

Developer and container files

• Delete ~/Library/Developer/Xcode/DerivedData and old versions in iOS DeviceSupport.
• Run xcrun simctl delete unavailable to remove simulators for runtimes you no longer have.
• Run docker system prune, or lower Docker Desktop's disk limit.
• Delete virtual machines you no longer use from inside their app.

App support data

Large folders in ~/Library/Application Support usually belong to an app: an old game, a music library, downloaded AI models. Remove the content from inside the app when you can, or delete the folder if you've already removed the app.

What not to delete

• Anything in /System, /usr, /bin or /private/var/db.
• The virtual memory and sleep files in /System/Volumes/VM — macOS manages them.
• Folders in /Library you don't recognize: they often belong to drivers or system components.

DiskGarden refuses to put system locations in the Waste bin, so you can explore freely without breaking anything.