System Data on a Mac: what it is and how to clear it safely

What System Data means

Open Apple menu, then System Settings, then General, then Storage and the bar at the top splits your disk into categories: Applications, Documents, Photos, iCloud Drive, macOS and so on. System Data is the one that's left over.

Apple's Storage settings guide describes it as files that don't fit the other categories, mostly data the system uses: log files, caches, virtual memory files and other runtime resources. It says macOS manages these and that the size changes with the state of your Mac. It also says, plainly, "You can't manage the contents of this category." Older versions of macOS called the same bucket Other, and Apple's free up storage article still calls it System Data (or Other).

In practice System Data works as a remainder. Howard Oakley of The Eclectic Light Company explains that Storage settings adds up the categories it recognizes and counts the rest of the used space as System Data. So anything it can't attribute lands there, including local snapshots and files in folders no category claims.

Macintosh HD · 401 GB of 500 GB used

Example numbers

• Applications64 GB
• Documents118 GB
• Developer52 GB
• Photos41 GB
• macOS22 GB
• System Data104 GB

What’s usually inside System Data

Caches

App, browser and system caches. Most refill on their own.

Local snapshots

Time Machine keeps these on the disk until it needs the space.

Virtual memory

Swap files and the sleep image, managed by macOS.

App data

Containers and support files in your Library.

Logs

Diagnostic and crash reports.

Purgeable

Space macOS can free by itself when an app needs it.

What's usually inside System Data

The mix is different on every Mac, but the same few things come up again and again.

• Local Time Machine snapshots. With automatic backups on, Time Machine saves a snapshot of your startup disk about every hour and keeps it for 24 hours. It also keeps one of your last successful backup until space is needed, and another before each macOS update. Apple's snapshot article says your Mac counts this space as available, which is why it can show up as System Data and as free space at the same time. More in Time Machine local snapshots.
• Caches. Apps, browsers and macOS keep copies of things so they don't have to download or rebuild them. They live in ~/Library/Caches and in folders macOS manages itself.
• Swap and the sleep image. When apps need more memory than your Mac has, macOS writes some of it to disk. It lets those files go as memory frees up and after a restart.
• Logs and crash reports. Records apps and macOS keep for troubleshooting.
• App data in your Library. Containers, Group Containers and Application Support hold databases, downloaded media and offline files for apps like Messages, WhatsApp, Slack and Docker Desktop.
• Developer data. Xcode build data, simulators, device support files and package manager caches can reach tens of gigabytes on a developer's Mac.
• Content macOS downloads. Voices, dictionaries, language and Apple Intelligence models and simulator runtimes. macOS adds and removes these as features need them.

Some of this is purgeable: space macOS can free on its own when an app needs it. Purgeable space on a Mac explains how that is counted.

Why System Data keeps growing

Most of what's in System Data is meant to come and go. Time Machine makes a new snapshot every hour while automatic backups are on. Apps refill their caches as you use them. Swap grows when memory is tight and shrinks after a restart. That's why clearing caches often frees space only for a few days. Moving a cache that's back to full size by next week buys time, not room. The lasting wins are things that don't come back on their own: build data for projects you've finished, simulators for runtimes you removed, and data left behind by apps you no longer have.

Two moments tend to make it jump. After a macOS update, Time Machine keeps the snapshot it took before installing, and macOS may download content for new features. And if you work with virtual machines, Docker or Xcode, their disk images and build data grow quietly in the background. Apple Community threads describe System Data well past 100 GB, often for one of these reasons.

A large number by itself isn't a fault. Apple's storage guide says that when space is needed, macOS clears caches and logs that are safe to delete, such as temporary database files, interrupted downloads, staged updates and Safari website data. The work is in finding the part that won't clear itself.

Where to look for each cause

Match the cause to your Mac before you move anything. Each row points to the place where that kind of data lives.

First, read what macOS already shows

Start in Storage settings. Hover over the bar to see each category's size, and click the Info button next to a category to see what's in it. Check the categories you can act on before you chase System Data. Documents lists large files and downloads, and has a file browser that shows folder sizes. iOS Files holds iPhone and iPad backups, and Trash shows what's waiting to be emptied. These are often quicker wins than anything in System Data. Give the bar time: it can show Calculating for a while on a full disk. If the numbers themselves look wrong, why Mac storage doesn't add up explains the usual reasons.

Disk Utility shows two things Storage settings doesn't. Open Disk Utility, choose View > Show All Devices, and select your startup volume: the Info button shows how much of the used space is purgeable. Choose View > Show APFS Snapshots to list local snapshots with their sizes, as Apple's Disk Utility guide describes.

How to reduce System Data, step by step

These steps start with what costs nothing and end with what you choose to move. They work the same on macOS 15 Sequoia, macOS 26 Tahoe and macOS 27 Golden Gate.

1. 1

   Read the numbers first

   Choose Apple menu > System Settings, click General, then Storage. Wait for the bar to finish calculating and note how big System Data is next to the other categories.

2. 2

   Restart your Mac

   macOS lets go of swap files at restart, so System Data often drops after one.

3. 3

   Check for local Time Machine snapshots

   In Terminal, run tmutil listlocalsnapshots /. If there are many and you need the space now, set Time Machine's Backup Frequency to Manually, wait a few minutes, then set it back.

4. 4

   Find the big folders in your Library

   In Finder, choose Go > Go to Folder, enter ~/Library, then select Caches, Logs, Developer, Containers and Application Support one at a time and press Command-I to see each one's size.

5. 5

   Move what you no longer need to the Trash

   Good candidates are old logs, caches of apps you've removed, Xcode build data and simulators you don't use. Leave the data of apps you still use where it is.

6. 6

   Empty the Trash when you're sure

   Items in the Trash still use space. It comes back only when you empty the Trash.

For step 3, Apple's way to remove local snapshots is to pause automatic backups. Open System Settings, then General, then Time Machine, then Options…, set Backup Frequency to Manually, click Done, and wait a few minutes. Then set it back to Automatically Every Hour, or whatever you had before. Until you do, your Mac isn't backing up on its own.

For step 4, the Library folder is hidden in Finder, so use Shift⌘G (Go to Folder) and type ~/Library. Select a folder and press ⌘I to see its size. The field guide explains what about 220 common folders are and whether they come back.

Checking System Data in Terminal

Terminal is good for looking. These two commands only read.

List local Time Machine snapshots of the startup disk:

tmutil listlocalsnapshots /

Show the biggest folders in your Library, largest last:

du -sh ~/Library/* 2>/dev/null | sort -h | tail -n 15

du -h counts in powers of 1,024, so its figures look about 7% smaller than the ones in Finder and System Settings, which count in powers of 1,000. Without Full Disk Access for Terminal, folders such as Mail and Safari may show as smaller than they are.

If simulators are the big item, Xcode's own tool removes simulators whose runtime is no longer installed. This deletes them permanently and skips the Trash:

xcrun simctl delete unavailable

Delete iOS simulators and clear Xcode DerivedData cover the developer side in more detail.

Be wary of advice to run sudo rm -rf on folders under /private/var, /System or /Library. rm skips the Trash and can't be undone. System Integrity Protection blocks changes to /System, and much of what it doesn't block is something macOS needs to run.

What's safe to clear and what to leave

/System/Library/AssetsV2

macOS downloaded content

Made by

macOS

What it is

Content macOS downloads as features need it: voices, fonts, dictionaries, language and Apple Intelligence models, and simulator runtimes.

Does it come back?

Comes back when it's needed

Without it

macOS protects this folder. It downloads and clears these items itself as features need them.

How to manage it

System Settings → General → Storage

System Data on macOS Tahoe and macOS 27

Apple's Storage settings guides for macOS 15 Sequoia, macOS 26 Tahoe and macOS 27 Golden Gate use the same path and the same definition of System Data, so everything above applies to all three. After Tahoe updates, several Apple Community threads reported System Data of several hundred gigabytes.

Two things explain much of the jump right after any update. Time Machine keeps the snapshot it took before installing, and macOS downloads content for features you use, such as Apple Intelligence models, which macOS adds and removes itself. Restart and give it a day before you conclude something is wrong. If System Data keeps growing for days and tmutil lists no snapshots, run the du command above again and see which folder grew.

How MacClearings explains System Data

MacClearings has a page for exactly this question. Breakdown starts from the same figures System Settings uses, read from macOS's own volume list. Then it measures the folders behind them and names each part in plain words: macOS, Apps, Your files, App data in your Library, and Shared and system data. Much of what Storage settings calls System Data turns out to be in your Library, and each folder there is explained in a sentence.

Local snapshots, purgeable space and swap get a "Frees on its own" label, because macOS frees them itself. Breakdown explains them and never offers them as a cleanup. Whatever MacClearings can't measure, such as the Spotlight index, document versions, or folders macOS hides until you allow Full Disk Access, is shown as a number at the bottom with the likely reasons. Breakdown only reads; it doesn't move anything.

When you want to act, Suggestions lists caches, logs and developer data, each with a plain reason. App and browser caches start unchecked, because apps rebuild them within days:

Suggestions rule · App caches

App caches

Temporary files apps keep to work faster. Apps recreate them as you use them, so moving them frees space only for a while, and the first launch afterwards may take a moment longer. They start unchecked.

• ~/Library/Caches/*

Listed, but you decide whether to check it.

You review the full list before anything moves. MacClearings moves what you confirm to the Trash, and History can undo the whole cleanup or put back a single item. The space comes back when you empty the Trash, which MacClearings never does for you. It also measures each cleaned place again after a day, a week and a month, so you can see which cleanups stayed free and which grew straight back.