# What is System Data on Mac, and why is it so big?

_Updated 2026-10-15_

Open **System Settings → General → Storage** and you get a bar of colours: Applications, Documents, Photos, macOS and so on. One grey segment is called **System Data**, and on many Macs it is the biggest one. It is also the one you cannot click to see what is inside.

System Data is the new name for what older versions of macOS called **Other**. The rename happened in macOS Ventura (macOS 13). The idea stayed the same: it is the catch-all for space that macOS cannot file under a named category.


## Why there is no folder called System Data

macOS sorts the files on your disk into categories. Applications are apps, Documents are files in your documents, Photos are your photo library, and macOS is the operating system itself. Whatever does not fit goes into System Data. So it is a total, not a place: it is made of many small and large things scattered across the disk.


## What usually ends up in System Data

The exact split varies between macOS versions, but these are the typical contents:

- **Caches.** Each app keeps temporary data in `~/Library/Caches`, and the system keeps its own in `/Library/Caches`. This is often the largest part, and the easiest to get back.
- **Logs and diagnostic reports.** Usually small, but they add up on a Mac that has run for years.
- **Swap and temporary files.** Virtual memory lives in `/private/var/vm` and is managed by macOS. Do not remove it by hand.
- **App support data, plug-ins and extensions.** Data apps store in `~/Library/Application Support`, plus containers in `~/Library/Containers`.
- **Snapshots.** APFS snapshots, for example the one macOS keeps after a system update, and Time Machine local snapshots.
- **Disk images, installers and indexes.** Downloaded `.dmg` files that were left behind, and indexes such as Spotlight's.
- **Developer and tool caches.** Xcode build files, package manager caches and AI model caches often land here instead of under Developer.


## Why it keeps growing

- Apps rarely clean their own caches, so they grow with use.
- Developer tools are the heaviest cache producers: a few Xcode projects can leave tens of gigabytes behind.
- Updates leave snapshots and installer files that macOS removes later, not immediately.
- Large downloads can sit in cache folders long after you stopped using the app that made them.


## Why the number in Settings jumps around

Storage settings calculates its figures in the background, so you may see Calculating, and the result can change a lot between two looks. On one test Mac the same System Data figure read about 66 GB at one moment and about 186 GB at another. Settings also counts things that no ordinary app can see, such as snapshots and purgeable space, so a tool that adds up files will land on a different number.

> This is why See Your Disk shows System Data as pieces: the folders it can trace (caches, logs, developer data) get their own blocks, and what it cannot trace stays as one separate block instead of being hidden.


## What is safe to remove, and what is not

| Usually safe to remove | Leave alone |
|---|---|
| Per-app caches in ~/Library/Caches | /System and anything under /private/var/db |
| Logs in ~/Library/Logs | Swap in /private/var/vm |
| Xcode DerivedData and old device support files | Snapshots macOS made for an update |
| npm, Gradle, pip and Homebrew download caches | The whole ~/Library/Containers folder |
| Old downloaded installers and disk images you no longer need | Docker's virtual disk file (use Docker's own cleanup instead) |


## How to see what is in yours

You can check the usual suspects in Terminal. These commands only read sizes:

```
du -sh ~/Library/Caches ~/Library/Developer ~/.cache ~/.npm 2>/dev/null
tmutil listlocalsnapshots /
diskutil apfs listSnapshots /
```

If you would rather see it, [See Your Disk](/) draws the whole disk as a map of blocks and marks the parts that are safe to clean. When you are ready to act, read [how to clear System Data on Mac safely](/guides/how-to-clear-system-data-on-mac/).

Get See Your Disk: [Mac App Store](https://apps.apple.com/us/app/clean-systemdata-seeyourdisk/id6817565741) · [GitHub](https://github.com/bikmeev/see-your-disk)

## Frequently asked questions

**Is System Data the same as Other?**
Yes. Before macOS Ventura (macOS 13) the same category was called Other. It is the catch-all for space that macOS cannot sort into a named category.

**Can I delete System Data completely?**
No. It is not one folder or one file, and it contains things macOS needs, such as swap and system indexes. You reduce it by removing specific items inside it, mainly caches, logs and old leftovers.

**Why is System Data bigger than the files I can find?**
Storage settings also counts things you cannot browse, such as APFS snapshots, purgeable space and metadata. File-based tools can only add up what they can see, so the figures rarely match exactly.

**Is a huge System Data a sign of malware?**
Usually not. The common causes are ordinary: app caches, developer tools, snapshots after an update and large cached downloads. If it is unexplained and growing fast, check which folders are large before assuming the worst.

## Related guides

- [How to clear System Data on Mac safely](https://seeyourdisk.com/guides/how-to-clear-system-data-on-mac/)
- [How See Your Disk cleans: methods and safety levels](https://seeyourdisk.com/guides/how-see-your-disk-cleans/)