In short
- After a scan, click System Data, explained in the sidebar. MoreRoom shows the whole startup disk: your files and apps, what isn’t visible without admin access, and each macOS volume.
- Scan Macintosh HD (Scan My Mac) to split your data into what MoreRoom can see and what is hidden — snapshots, root-only folders, file system metadata.
- macOS volumes (the sealed system, Preboot, Recovery, virtual memory, updates) can’t be reduced by hand; the rest of System Data often can.
Open the screen
Scan your Mac, then click System Data, explained in the sidebar. MoreRoom reads the layout of the startup disk directly from macOS — it takes a moment the first time (“Reading the startup disk…”).
The breakdown
The bar and the list show where every gigabyte of the startup disk goes:
| Part | What it is | Can you reduce it? |
|---|---|---|
| Your files and apps | Everything MoreRoom can see and map | Yes — that’s what the map and Free Up Space are for |
| Not visible without admin access | Root-only folders, local snapshots and file system metadata | Partly: snapshots expire on their own; see below |
| macOS (sealed system) | The read-only system signed by Apple | No |
| Virtual memory (swap, sleep image) | Grows with memory pressure | It shrinks after a restart |
| Preboot (startup files) | Firmware and boot data for each installed macOS | No |
| Recovery | Used to repair or reinstall macOS | No |
| Software updates | Prepared updates waiting to be installed | Install the update, and the space comes back |
If you scanned your home folder or another folder instead, MoreRoom can’t split your data volume and shows it as one line, Your data volume, with a reminder to scan Macintosh HD.
Why the numbers differ
The Why the numbers differ card explains the usual surprises:
- Finder shows more free space than df: Finder adds “purgeable” space — caches and snapshots macOS promises to delete when it needs room.
- Local snapshots: Time Machine and backup apps keep snapshots that hold deleted files until they expire. The card says how many there are right now.
- Some folders need admin access: system caches, other users and diagnostic data are root-only, so MoreRoom counts them in the “not visible” part instead of hiding them.
- macOS reserves its own volumes: the sealed system, Preboot, Recovery, VM and Update live outside your data and are counted as System Data by System Settings.
Read more in our guides: What is System Data?, Purgeable space and Time Machine local snapshots.
Get System Data down
- Look at Free Up Space: many caches that System Settings counts as System Data are in your Library and recognised by MoreRoom.
- Restart your Mac if virtual memory is large.
- Install pending macOS updates.
- Let local snapshots expire, or see Space didn’t come back.