Mac System Data Storage: What It Is, How to Clear It

System Data (formerly Other) is the catch-all for files macOS didn’t put in another category: usually Time Machine local snapshots, caches, swap and app data in your Library folder. Don’t delete it blindly — find out what actually grew first, then remove that the proper way.

Large System Data isn’t a diagnosis, it’s a question: what exactly ended up in there.

Where to look

System Settings → General → Storage. At the top is a bar of the disk by category, below it a list: Applications, Documents, macOS, System Data and others. Most categories have an ⓘ button that opens the files and lets you delete them. System Data has none: it isn’t a folder but a remainder — everything that didn’t fit another category.

According to Apple, it’s a general category for files from Apple and third-party apps that don’t fit a more specific one. In older versions of macOS it was called Other.

Right after you open it, Settings is still calculating sizes, and the numbers may shift. Give it a minute.

What’s usually in System Data

Time Machine local snapshots

If Time Machine is on, the Mac takes snapshots of the startup disk right on that disk. According to Apple: about once an hour, each kept for 24 hours, plus a snapshot of the last successful backup and one before every macOS update. Snapshots are deleted automatically as they age or when space is needed — and Apple counts the space they use as available: they don’t stop you from downloading a file or installing an app.

To see them:

tmutil listlocalsnapshots /

To remove them right away, Apple suggests: System Settings → General → Time Machine → Options, set Backup Frequency to Manually, wait a few minutes, then set the frequency back.

Swap files

When memory runs short, macOS moves some of it to disk, into swap files. To see how much there is right now:

sysctl vm.swapusage

Swap goes away after a restart and grows again if memory is tight. Where it comes from and how much is normal is in the swap guide.

Caches and app data

Browsers, messengers, music and video services and development tools keep caches and working files in the hidden Library folder of your user account. Virtual machine and container images end up there too. That’s usually where tens of gigabytes hide.

How to find what grew

Start with the regular categories. In the same Storage pane, open ⓘ next to Applications, Documents and Trash — some of the “extra” is there, and it’s easier to remove.
Check folder sizes in Library. In Terminal (Applications → Utilities → Terminal):
```
du -xhd 1 ~/Library 2>/dev/null | sort -h | tail -15
```
The command only reads, and lists the 15 largest folders at the end. Without extra permission for Terminal it silently skips some folders — usually that’s still enough to find the big ones.
Go one level deeper into the largest folder — for example ~/Library/Caches or ~/Library/Containers — with the same command and a different path. The folder name almost always points to the app.
Open the folder in Finder if you’d rather look: Go → Go to Folder (⇧⌘G), type ~/Library.

What to do with what you find

An app’s cache — clear it in that app’s settings: browsers, messengers and streaming services have a button to clear the cache or downloads. A cache deleted by hand gets downloaded and rebuilt.
An app you no longer use — remove it completely, along with its data in Library. How to find what it leaves behind is in the guide to app size and uninstalling.
Virtual machine and container images — remove them from inside the app itself: machines, images and volumes you don’t need.
Old iPhone and iPad backups — Apple suggests deleting the ones you don’t need; they’re under iOS Files in Storage (if that category is there) or in Finder with the device connected.

Apple also reminds you that space is freed only once the Trash is emptied, and that starting up in safe mode temporarily clears some system caches (Apple).

macOS recommendations

At the bottom of Storage are Recommendations: Store in iCloud, Optimize Storage (remove Apple TV movies and shows you’ve watched and keep only recent Mail attachments) and Empty Trash Automatically (after 30 days). They don’t touch System Data directly, but they free space without going into system folders.

What not to do

Don’t delete anything in /System, /private/var or /Library at the root of the disk. Those are macOS’s own files and installed services; after a “cleanup” the Mac may not start.
Don’t delete swap files or snapshots by hand in Finder. A restart frees swap; Time Machine removes snapshots (see above).
Don’t install “cleaners” for System Data. They delete the same caches that apps immediately recreate, and they run in the background themselves.

Low on space and the Mac is slow

A nearly full disk slows things down by itself: macOS needs free space for swap, updates and temporary files. If your Mac is also slow, walk through the step-by-step diagnosis — step 3 is about the disk. If it’s SSD wear rather than space that worries you, see the SSD wear guide.

In the app

To be clear up front: Mac Resources doesn’t show what’s on the disk or how big System Data is — that’s the job of Storage and du.

What the app gives you alongside:

the small Disk widget — how full the system volume is, a graph for the past hour and a figure like “2.4 of 4.0 TB”. It counts free space the same way Finder does, in base 1000, so the numbers match;
the hourly graph shows when space is vanishing before your eyes: something is writing a lot right now — swap, a download, an export. Who exactly is on the Disk tab in Activity Monitor.

The app is free and runs on macOS 14 and later.