# Understand System Data with MoreRoom

> How MoreRoom’s System Data screen splits your startup disk into your files, hidden areas and macOS volumes, and why Finder and Settings disagree.

- URL: https://moreroom.app/support/system-data-screen
- Topic: Freeing up space
- Updated: 2026-10-17
- Publisher: MoreRoom (Yando Pte. Ltd.) — https://moreroom.app

## 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?](https://moreroom.app/learn/what-is-system-data-mac), [Purgeable space](https://moreroom.app/learn/purgeable-space-mac) and [Time Machine local snapshots](https://moreroom.app/learn/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](https://moreroom.app/support/space-not-back).

## Related articles

- [Why MoreRoom’s numbers differ from Finder and System Settings](https://moreroom.app/support/numbers-differ.md)
- [I removed files, but my free space didn’t come back](https://moreroom.app/support/space-not-back.md)
- [Free Up Space and goal mode](https://moreroom.app/support/free-up-space-goal-mode.md)
- [Scan your Mac, your home folder or any folder](https://moreroom.app/support/scan-your-mac.md)

## Still need help?

Write to us: a real person reads every message and answers within 2 business days. https://moreroom.app/contact