Why is System Data so large on my Mac?

What System Data actually is

Apple describes System Data (called Other on older versions of macOS) as a general category for the storage used by all Apple and third-party files that don't belong to a more specific category. It is not one folder. It is whatever is left after macOS has counted your apps, documents, photos, mail, messages, iCloud Drive files and the other named categories.

That's why it's confusing: Storage settings shows System Data as one grey block, and there is no button that lists what's inside it. On a Mac that has been in use for a while, it can include:

• Caches and logs. Apps and macOS keep cached data and write logs. Apple notes that macOS clears caches and logs that are safe to delete by itself, including temporary database files, interrupted downloads, staged macOS and app updates, and Safari website data.
• Time Machine local snapshots. If Time Machine backs up automatically, macOS saves a snapshot of your startup disk about once an hour and keeps it for 24 hours. It also keeps a snapshot of your last successful backup until the space is needed. Apple counts the space used by snapshots as available storage, and Time Machine deletes snapshots as they age or when the space is needed.
• App data in your Library folder. Many apps keep large data under ~/Library, for example virtual machines, downloaded models, offline media or developer tools. Data that doesn't fit a named category ends up in System Data.

Because snapshot space counts as available, Finder and Storage settings can report different amounts of free space. Neither number is wrong. They count snapshots and other purgeable data differently.

How to investigate System Data with macOS tools

These steps use the System Settings layout from macOS Ventura 13 onwards, including macOS 27.

1. Read the real numbers

Choose Apple menu › System Settings, click General in the sidebar, then click Storage. Wait until every category has finished calculating; System Data can look very large while the other categories are still being counted.

2. Check for Time Machine local snapshots

Open Terminal (in Applications › Utilities) and run this command. It only lists snapshots and changes nothing:

tmutil listlocalsnapshots /

Each line is one snapshot. macOS removes them on its own when the space is needed. If you need the space right now, follow Apple's method:

1. Choose Apple menu › System Settings › General › Time Machine.
2. Click Options…, choose Manually from the Backup Frequency menu, then click Done.
3. Wait a few minutes while the local snapshots are deleted.
4. Set Backup Frequency back to your usual automatic setting.

Turn automatic backups back on when you're done. Snapshots let you restore recent versions of your files.

3. Find which apps keep the most data

1. In Finder, choose Go › Go to Folder…, type ~/Library and press Return.
2. Choose View › as List, then View › Show View Options and turn on Calculate all sizes.
3. Click the Size column to sort. Open the largest folders (usually Application Support, Containers, Group Containers, Caches or Developer) and sort those by size too.

Look for names you recognise: a virtual machine app, a container tool, a model runner, a game launcher, a video editor. Once you know which app owns the space, remove downloads, models, disk images or caches through that app's own settings. If you no longer use the app, uninstall it, then check whether its folder in Application Support is still there.

If the largest folder is Developer and you build software, see how to clear Xcode DerivedData.

4. Treat caches as a fix, not a strategy

~/Library/Caches holds caches for each app. Apps rebuild their caches as you use them, so clearing them doesn't free space for long. Only clear one app's cache, with that app quit, when you have a specific reason, such as the app misbehaving.