System is 30 GB or more, and almost none of it is removable
The System category covers the sealed volume, asset packs and recovery data. What each part is and the two things you can change.
The storage screen shows a System figure that is often larger than any application you have installed, offers no way into it, and no explanation. It is made of four things, and only two of them are anything you can act on.
What is in it
| Component | Roughly | Removable |
|---|---|---|
| The sealed system volume | 15 to 25 GB | No, and it is read only |
| Downloadable asset packs | 2 to 30 GB | Partly |
| Recovery and Preboot volumes | 1 to 2 GB | No |
| Sleep image and swap | Equal to memory | Only by changing hibernation |
The one that varies wildly
Asset packs are the reason two Macs running the same macOS report very different System figures. On a developer machine, simulator runtimes stored as system assets can be 25 GB on their own, which is covered in Apple's downloadable asset packs. On a Mac with several languages configured, Siri and speech data is the larger part.
du -sk /System/Library/AssetsV2/* 2>/dev/null | sort -n | tail -10 \
| awk '{printf "%5d MB\t%s\n", $1/1024, $2}'The two things you can actually change
- Remove simulator runtimes you do not target, with
xcrun simctl runtime delete. This is the largest single reduction available on a developer Mac. - Remove languages you do not use, in System Settings, which takes their dictionaries, spelling and Siri models with them.
What not to try
The system volume is sealed and cryptographically verified, so it cannot be modified even with administrator rights, and attempting to work around that produces a Mac that will not boot. Any tool claiming to shrink macOS itself is describing something else, which is one of the storage myths worth retiring.
System against System Data
These are two different categories and they are constantly confused. System is macOS itself and its assets. System Data is everything macOS cannot classify: caches, logs, snapshots and app support files, which is where the space you can actually reclaim usually is. What System Data is made of covers that side.
Common questions
Why is System storage so large on my Mac?
It combines the sealed system volume, recovery volumes, the sleep image sized to your memory, and downloadable asset packs. Asset packs are why two Macs on the same macOS can differ by tens of gigabytes.
Can I reduce System storage on a Mac?
Two things work: removing simulator runtimes you do not target, and removing languages you do not use. The system volume itself is sealed and read only and cannot be shrunk.
What is the difference between System and System Data?
System is macOS itself plus its assets and recovery volumes. System Data is everything macOS cannot classify, such as caches, logs, snapshots and app support files, which is where reclaimable space usually is.
Is it safe to delete files from /System?
No, and it is not possible on modern macOS. The volume is sealed and cryptographically verified, and attempting to modify it produces a Mac that will not boot.