You check your Mac's storage and find that your Documents, Apps, and Photos take up barely any space, but a massive, grey bar labeled "System Data" (or "Other" on older macOS versions) is eating up 50GB or more of your hard drive.

What actually is 'System Data' on a Mac? System Data is a catch-all category used by macOS that includes:

  • Time Machine Local Snapshots: Hidden backup files stored locally when your external drive isn't connected.
  • System and User Caches: Temporary files created by Safari, Xcode, Spotify, and other apps to load faster.
  • Old iOS Backups: Massive files created when you sync or back up an iPhone or iPad to your Mac.

Because Apple hides these files deep within the Library folder to prevent you from accidentally breaking the operating system, it can be terrifying to try and clean them. Here is a safe, step-by-step guide to clearing the System Data on your Mac without causing any damage.

What Actually is 'System Data' on a Mac?

When you open System Settings > General > Storage, Apple categorizes your files. Anything that isn't explicitly an app, a photo, a document, or an audio file gets thrown into the "System Data" bucket.

While some of this data is essential (like the actual macOS operating system files, which usually take up about 15-20GB), the rest is completely expendable. The problem is that a single heavy app (like a video editor or a music streaming service) can generate 20GB of cache files over a year. Furthermore, if you use Time Machine, your Mac silently hoards backup files on its internal drive "just in case."

Step 1: Removing Local Time Machine Snapshots

The number one reason for a bloated System Data bar is local Time Machine snapshots. When your external backup drive is unplugged, your Mac continues making daily backups and saves them locally.

While macOS is supposed to delete these automatically when space runs low, it often fails to do so. You can safely force-delete them.

How to delete local snapshots (Safe Method):

  1. Connect your external Time Machine drive and let a backup complete. Once done, macOS will usually clear the local snapshots automatically.

How to delete local snapshots via Terminal: If you don't have your drive, you can use the Terminal.

  1. Open the Terminal app (Command + Space, type Terminal).
  2. Type the following command and hit Enter: tmutil listlocalsnapshots /
  3. You will see a list of dates.
  4. To delete them all at once, type this command and hit Enter: sudo tmutil thinlocalsnapshots / 10000000000 4 (You will need to enter your Mac login password).

This command forces the system to thin out old snapshots, immediately recovering gigabytes of System Data.

Step 2: Safely Clearing User and System Caches

Every app on your Mac creates cache files. Over time, these files become obsolete but are never automatically deleted.

How to clear the User Cache:

  1. Open a Finder window.
  2. In the top menu bar, click Go, then hold down the Option (⌥) key on your keyboard.
  3. Click on the hidden Library option that appears in the dropdown menu.
  4. Open the Caches folder.
  5. Here, you will see folders for every app you use (e.g., com.apple.Safari or com.spotify.client).
  6. Important: Do not delete the folder itself. Press Command + A to select everything inside the Caches folder, then press Command + Delete to move the contents to the Trash.

Empty your Trash bin immediately. When you reopen your apps, they will simply generate fresh, much smaller cache files.

Step 3: Removing Old DMG Installers and iOS Backups

The final hidden culprits in the System Data category are old software installers and massive device backups.

Deleting DMG Files: Whenever you download a new app from the internet, it comes in a .dmg file. Once the app is installed, the DMG file is useless. Open Finder, go to your Downloads folder, type .dmg in the search bar, and delete all the leftover installer files.

Deleting Hidden iOS Backups: If you've ever plugged an iPhone or iPad into your Mac to sync or back it up, macOS saves a massive file (often 50GB+) on your hard drive.

  1. Open System Settings > General > Storage.
  2. Look for the category named iOS Files (or click the 'i' info icon next to it).
  3. If you see old backups for devices you no longer own, or if you now back up to iCloud, safely delete these massive local backups.

By addressing local snapshots, caches, and hidden backups, you can easily slash your System Data in half and get your Mac running smoothly again.