It is one of the most frustrating notifications on macOS: opening System Settings → General → Storage only to find an unclickable gray bar labeled System Data: 118 GB. Why does Apple hide what is inside, and how do you clean it?
What Actually Lives Inside System Data?
The core macOS operating system is sealed inside a cryptographically signed, read-only APFS volume that typically occupies only 15GB to 20GB. Everything else reported under System Data is temporary data accumulated by third-party applications:
-
•
User Application Caches (
~/Library/Caches): Video streaming buffers, browser databases, creative suite rendering caches, and messaging apps hoard uncompressed media indefinitely. -
•
Orphaned Application Support: When an app is moved to Trash, its support folder inside
~/Library/Application Support/remains on your disk forever. -
•
Runaway Diagnostic Logs (
~/Library/Logs): Background process loops can write hundreds of megabytes of crash logs each week. - • APFS Local Snapshots: Temporary Time Machine backup snapshots reserved directly on your internal SSD.
Discover how XrayMac concentric color rings and interactive sunburst treemaps visualize your entire Mac storage hierarchy in sub-second speed. Reclaims 30GB to 80GB Safely
Cleaning these directories manually in Finder is tedious and error-prone. XrayMac's Smart Care engine scans every subfolder within ~/Library, detects orphaned files from apps that are no longer installed, and allows you to purge them safely with a single click.