What is System Data on a Mac? Every part, explained

What is System Data on a Mac? It's the part of your storage that System Settings › General › Storage can't put in any other category. Apple describes it as files that don't fall into the listed categories: mostly files and data the system uses, such as logs, caches, virtual memory, temporary files, fonts, app support files and plug-ins.

It isn't a folder, and it isn't one kind of file. Storage settings adds up the categories it can measure, such as Applications, Documents and Photos, and calls whatever is left System Data.

That remainder takes in Time Machine's local snapshots, which live in no folder at all, along with caches, logs, swap files, app data and most developer files. So there's no button to empty it, and the number can change while you watch.

Most of it is normal and looks after itself. A few parts are worth your attention: snapshots that haven't been cleared yet, caches of apps you no longer use, developer files, and data left behind by apps you've deleted. This post takes System Data apart, piece by piece, and says which pieces are yours to remove and which are macOS's.

Every part of System Data at a glance

Here are the parts that make up System Data on most Macs, where each one lives, and who should remove it. The sections below go through each one in detail.

Part	Where it lives	Level	Who removes it
Time Machine local snapshots	No folder: inside the startup disk	Managed by macOS	Time Machine, or you in its settings
App caches	~/Library/Caches	Safe	You, with the app quit
Shared caches	/Library/Caches	Usually safe	An administrator
Temporary files	/private/var/folders, /private/tmp	Managed by macOS	macOS, by itself
Swap and sleep image	/private/var/vm	Managed by macOS	macOS; a restart clears swap
Logs and crash reports	~/Library/Logs, /Library/Logs	Safe to usually safe	You, or Console
App data	~/Library/Application Support, ~/Library/Containers	Review first	You, in the app
Developer files	~/Library/Developer and tools' own folders	Varies	The tool that made them

The levels are the ones this site's library uses. Safe means the owner recreates the item by itself and nothing is lost. Usually safe means it comes back at a cost, or needs an administrator. Review first means it may hold your own data. Managed by macOS means macOS handles it, and you leave it alone or use a setting.

If you only want to know why the number is so large, the short guide to System Data lists the usual suspects. Here, each part gets its own section.

What is System Data on a Mac, in Apple's words

Apple's guide to Storage settings says System Data contains files that don't fall into the categories it lists. It names examples: log files, caches, VM files and other runtime system resources, plus temporary files, fonts, app support files and plug-ins. The guide has said much the same since macOS Big Sur.

Apple also says you can't manage the contents of this category in Storage settings, that macOS manages them, and that the size varies with the current state of your Mac. For data outside the other categories, it points you to Finder or the apps that created it.

That's the key to the whole category. System Data is a picture of a moving system, not a fixed pile of files, and each part of it has an owner who manages it.

Where do you see System Data?

Choose Apple menu › System Settings, click General in the sidebar, then click Storage. The bar at the top shows used and available space, split into colors by category. Move the pointer over a color to see how much space that category uses.

Below the bar is the list of categories. Most have an information button that opens a list of the largest items, where you can delete them or show them in Finder. System Data, macOS and Other Users & Shared show only a size. Apple's guide says you can't select and delete files in them.

In macOS 26 Tahoe and macOS 27 Golden Gate, an All Volumes button shows a more detailed chart of the space used and available on each volume and container of the internal disk. It's useful when your Mac has more than one volume, but it doesn't break System Data down any further.

How does macOS work out the number?

Storage settings measures each category it knows, adds them up, and subtracts the total from the used space on the startup disk. What's left is System Data. Howard Oakley of Eclectic Light, who has written about this in detail, calls it a rough estimate rather than a measured figure.

macOS itself, on its sealed system volume, is counted separately under macOS, so System Data doesn't include the system files you can't change anyway.

Because it's a remainder, System Data absorbs every error in the other categories. If a category counts too little, System Data counts too much. That's why it can jump while Storage settings finishes its calculations, and why it rarely matches what you'd get by adding up folders in Finder.

Was System Data called "Other" before?

Yes. Before macOS Monterey, the same leftover category was called Other, and the storage view lived in About This Mac. The name changed, and so did a few details of what's counted where.

macOS version	Where you look	What the leftover category is called
Big Sur 11 and earlier	Apple menu › About This Mac › Storage	Other, with macOS listed as System
Monterey 12	About This Mac › Storage › Manage	System Data
Ventura 13 to Sequoia 15	System Settings › General › Storage	System Data
Tahoe 26 and Golden Gate 27	System Settings › General › Storage	System Data, with All Volumes beside the bar

One detail changed with the rename. Apple's Big Sur guide listed Time Machine's local snapshots as part of the System category. In later versions, the examples for macOS no longer mention them, and snapshots end up in System Data, which has no Time Machine category of its own.

System Data vs macOS, Documents and the other categories

A lot of confusion about System Data comes from guessing which category a big item belongs to. Several of the largest things on a Mac are counted somewhere else entirely.

What's the difference between System Data and macOS?

macOS holds macOS's own apps and files, such as Mail, Terminal and Calculator. They sit on a sealed, read-only system volume that only Apple's updates change. On Macs that support Apple Intelligence, its models are counted here too: Apple says they need up to 8 GB, or up to 14 GB on some newer Macs.

System Data is everything else that no other category claims. It includes files macOS manages, such as swap and temporary folders, and files apps manage, such as caches and app data. The two are easy to mix up because both sound like "the system", but only System Data has parts you can do something about.

Are iPhone backups part of System Data?

No, although many guides say so. Apple's guide puts iPhone and iPad backups, and the software files Finder downloads to update them, in the iOS Files category. Click its information button to see and delete them.

The same goes for a few other large items people often blame on System Data. Messages attachments are counted under Messages, mail under Mail, and GarageBand and Logic content under Music Creation.

Where does each large item show up?

Item	Category in Storage settings	Where to manage it
iPhone and iPad backups	iOS Files	Storage settings, or Finder with the device connected
Messages attachments	Messages	Storage settings, or Messages
Apple Intelligence models	macOS	System Settings › Apple Intelligence & Siri
Some Xcode build and device support files	Developer, on a Mac with Xcode	Storage settings, or Xcode
Time Machine local snapshots	System Data	Time Machine settings, or Disk Utility
App caches and app data	System Data	Finder, or the app itself
Other accounts' files	Other Users & Shared	Their own account, or Users & Groups

Why are some of your own files counted as System Data?

The categories don't always catch everything. Oakley found that Storage settings counted under 50 GB of a Music folder that held over 100 GB, because files outside the Music app's library aren't counted under Music. Used space that no category claims ends up in the remainder.

Files outside your home folder are another source. Apple's guide says Documents holds files in your home folder that aren't in another category. Shared caches in the Library folder at the top of the disk, and tools installed outside your home folder, have no category to go to.

Time Machine's local snapshots: the part no folder shows

If you back up with Time Machine, local snapshots are often the single largest part of System Data, and the hardest to see. A snapshot is a record of your startup disk at one moment, kept on the disk itself so you can restore files even when your backup disk isn't connected.

Apple says Time Machine saves a snapshot about every hour and keeps each one for 24 hours. It also keeps a snapshot of your last successful backup until the space is needed, and macOS saves one before each macOS update.

Why do snapshots take up space?

A snapshot holds on to the files as they were when it was taken. Delete a 20 GB video, and the space stays in use until every snapshot that still includes the video is gone. If you change large files often, the snapshots grow with them.

Apple says your Mac counts the space snapshots use as available, and that Time Machine removes them as they age or when space is needed. That's why Finder can show plenty of available space while Storage settings shows a large System Data figure.

They're describing the same space in two ways: Finder as space macOS can free when asked, Storage settings as space still in use.

How do you see your snapshots?

Open Disk Utility, in the Utilities folder inside Applications. Choose View › Show APFS Snapshots, then select your startup disk's volume in the sidebar. Its snapshots appear in a table at the bottom of the window, with the date each was taken.

For a sense of their size, click the More pop-up menu, choose Show Columns, and turn on Private Size and Cumulative Size. Snapshots share data with each other and with your files, so there's no exact size for each one. Choose View › Hide APFS Snapshots when you're done.

Should you remove local snapshots?

Usually not. Time Machine removes them by itself, and they're your quickest way back to a file you deleted this morning. They become a problem only when something needs the space before macOS gets round to freeing it, such as a macOS update or a large copy.

When you need the space now, open System Settings › General › Time Machine, click Options, set Backup Frequency to Manually and click Done. Wait a few minutes, then set it back. To remove one snapshot, select it in Disk Utility's snapshot table and click Delete Snapshot.

Either way, you can no longer restore files from the removed snapshots. Backups on your Time Machine disk aren't affected. The guide to Time Machine local snapshots also covers snapshots made by other backup apps, and what to do when you no longer have a backup disk.

Caches: the largest part you can clear yourself

A cache is data an app keeps so it doesn't have to fetch or work it out again: downloaded images, compiled code, thumbnails, previews. Apple's guidelines for developers say an app should keep only data it can recreate in its Caches folder. Caches live in several places, and each place has its own rules.

Which caches are in System Data?

• ~/Library/Caches holds a folder for each app and service, named after the app or its identifier, such as com.apple.Music. These are the caches you can clear yourself. Folders from apps you've deleted stay here until you remove them.
• Sandboxed apps, which include most apps from the App Store, keep their caches inside their own container in ~/Library/Containers, in a Caches folder within the container's Data and Library folders.
• /Library/Caches, in the Library folder at the top of your disk, holds caches shared by every user account. Most items belong to macOS or an administrator, so removing them needs an administrator's password.
• /private/var/folders holds a private cache and temporary folder for each user account. macOS manages it, and you leave it alone.

Is it safe to delete caches?

For the caches in your own Library folder, yes. Quit the app first, so it isn't writing to its cache while you remove it. The app rebuilds what it needs, which makes it slower for a while, and some apps download data again.

Clearing caches frees space. It doesn't make a Mac faster, and the space comes back as you use your apps. It's most worthwhile for caches of apps you've removed, and for one app whose cache has grown far beyond the others.

The post on how to clear cache on a Mac goes through every kind, from browsers and apps with their own buttons to developer tools.

macOS also clears some caches by itself. When space is needed, Apple says it removes caches and logs that are safe to delete, such as temporary database files, interrupted downloads, staged updates and Safari's website data.

Does safe mode clear System Data?

Partly. Apple says starting up in safe mode clears some system caches, including font and kernel caches, which macOS rebuilds as needed. It can free a little space for a one-off job such as installing an update. The caches come back once you use your Mac normally.

On a Mac with Apple silicon, shut down, then press and hold the power button until you see Loading startup options. Select your startup disk, hold Shift and click Continue in Safe Mode.

On an Intel-based Mac, turn it on or restart it, then press and hold Shift right away, and let go when the login window appears. To leave safe mode, choose Apple menu › Restart.

Logs, crash reports and diagnostics

macOS and apps keep records of what they do, and of what went wrong. Most of these are small and look after themselves. A few can grow, usually because one app writes far more than it should.

Which logs can you remove?

Part	Where	Level	What to do
App logs	~/Library/Logs	Safe	Move what's inside to the Trash; keep the folders
Crash and diagnostic reports	~/Library/Logs/DiagnosticReports	Safe	Move them to the Trash in Console
Logs for all users	/Library/Logs	Usually safe	Needs an administrator; keep the folders
System log files	/private/var/log	Managed by macOS	Leave them: macOS rotates them
The unified log	/private/var/db/diagnostics	Managed by macOS	Leave it: macOS limits its size
Core dumps	/cores	Review first	Exist only if someone turned them on

Keep the log folders themselves when you clear logs. Some programs, including background jobs, expect them to exist.

What is the unified log?

Most of what macOS and apps record now goes to the unified log, in a compressed format that the Console app reads. The service that keeps it removes the oldest entries as new ones arrive, so it stays about the same size.

macOS still writes a few plain text logs in /private/var/log, such as install.log. It rotates them on a schedule, compressing older copies and removing the oldest, so they stay within set limits.

How do you clear crash reports?

Open Console, in the Utilities folder. Under Reports in the sidebar, select Crash Reports, Spin Reports, Log Reports or Diagnostic Reports. Select a report at the top of the window, then choose File › Move to Trash. Administrators can see reports for the whole system as well as their own.

Nothing on your Mac needs these reports. They help a developer or Apple understand a problem, so keep any you're about to send with a bug report. macOS writes a new one if something crashes again.

What are core dumps?

A core dump is a copy of a crashed program's memory, saved in /cores. macOS writes them only if someone has turned them on, usually a developer examining a crash in a debugger. Each one holds a program's whole memory, so they can be very large. If you find them and no longer need them, they can go.

Virtual memory, temporary files and other parts macOS runs itself

Several parts of System Data belong to macOS while it runs. They take real space, and some can be large, but the right move is to let macOS handle them, or to use the one setting that controls them.

Swap files and the sleep image

When apps need more memory than your Mac has, macOS moves some of it to swap files on the startup disk. It can also save the contents of memory to a sleep image, so your work is safe during a long sleep. Both live in /private/var/vm.

To see how much swap is in use, open Activity Monitor, click Memory, and look at Swap Used at the bottom of the window. Restarting clears the swap files. Quitting apps that use a lot of memory keeps them small. Removing these files yourself while macOS uses them can make your Mac stop responding.

Temporary files

Apps and macOS keep short-lived files in two places. /private/var/folders holds a private temporary folder and cache folder for each user account, with random names. macOS removes temporary items there that haven't been used for three days, but the cache part isn't cleared on a schedule, so it can grow.

/private/tmp, also known as /tmp, is shared by every user and process. Each day, macOS removes items that haven't been opened or changed for three days. Leave both folders to macOS: removing files an app is using can make it lose work in progress.

The Spotlight index

Spotlight keeps an index of each disk in a hidden .Spotlight-V100 folder at the top of the disk, and a separate index of content inside apps, such as mail and notes, in ~/Library/Metadata/CoreSpotlight. Both are normally modest. Some people have seen them grow to well over 100 GB when indexing goes wrong.

If you suspect the disk's index, rebuild it rather than deleting it. Open System Settings › Spotlight and click Search Privacy. Add your startup disk to the list, wait a few seconds, select it again and click the remove button, then click Done. Spotlight indexes the disk again, and searches are incomplete until it finishes.

Document versions, the Rosetta cache and downloaded parts of macOS

A few smaller parts belong to macOS too:

• Document versions. Apps such as Pages, TextEdit and Preview save earlier versions of your documents in a hidden folder at the top of the disk. To remove one, open the document, choose File › Revert To › Browse All Versions, select the version, then choose File › Revert To › Delete This Version.
• The Rosetta cache. On a Mac with Apple silicon, Rosetta keeps translated copies of apps made for Intel processors in /private/var/db/oah. It grows only when you use such apps; versions built for Apple silicon don't need it.
• Downloaded assets. macOS downloads speech and language data, voices, fonts and dictionaries separately from the system, and adds or removes them as features need them.
• Software update files. Software Update keeps information about available updates, and some downloads, in /Library/Updates. Installing pending updates lets it remove the files it no longer needs.

App data: Application Support, Containers and Group Containers

Apple's examples for System Data include app support files. Apps keep the data they manage for you in three places in your Library folder, and this is where System Data stops being about caches and starts being about your own work.

What's in Application Support?

~/Library/Application Support holds a folder for each app: libraries, databases, downloads and settings. It can include your own data, such as a library, a chat history or projects saved only inside the app. A second Application Support folder, in the Library folder at the top of the disk, is shared by all users.

Sandboxed apps keep the same kinds of data in their own container in ~/Library/Containers. Apps from one developer that share data, such as an app and its widgets, use a group container in ~/Library/Group Containers.

Can you delete Application Support folders?

Not as a whole, and not without looking. These folders are Review first: some of what's inside can't be made again. Manage the data in the app itself, for example by removing downloads or old projects there, or use the app's own uninstaller if it has one.

Deleting an app doesn't remove its folders here, so apps you removed years ago can still hold space. Before you move such a folder to the Trash, open it and check that nothing in it is still needed. The guide to uninstalling apps properly goes through each place an app leaves things.

Are preferences part of System Data?

They live in your Library folder too, but they aren't worth removing. An app's preferences and its saved window state are tiny files. Removing them frees almost nothing and only resets the app, so leave them alone.

Developer files and local AI models

On a developer's Mac, tools often make up most of System Data. Their files sit in your Library folder or in hidden folders in your home folder, and some of them run to tens of gigabytes.

Xcode, simulators and runtimes

Xcode keeps build products for every project in DerivedData, a simulator for every device you've tested on, runtimes for every OS version you've installed, and debug symbols for every OS version your devices have run. Storage settings counts some of this under Developer, and the rest in System Data.

DerivedData is Safe: Xcode rebuilds it. Simulator runtimes are managed through Xcode's Components settings, never in Finder. Archives of builds you shipped are worth keeping. The post on why Xcode takes up so much space goes through every folder.

Docker, virtual machines and package caches

Docker Desktop keeps every image, container and volume in one disk image file. Don't delete it: remove what you don't need in Docker Desktop instead. Virtual machines from UTM, Parallels and similar apps each hold a whole computer's disk, and belong to the app that made them.

Package managers such as npm, pip, uv and Homebrew keep a cache of what they download. Each can download it again, and most have their own cleanup command.

Local AI models

Tools such as Ollama and LM Studio keep every model you download until you remove it, and a single model can take several gigabytes or more. Remove models in the tool that downloaded them, because some tools share files between models.

• App caches2–30 GB · Safe
• Shared caches1–10 GB · Usually safe
• Logs and crash reports0.1–5 GB · Safe
• Per-user temporary files1–70 GB · Managed by macOS
• Swap and sleep image1–20 GB · Managed by macOS
• Rosetta cache1–10 GB · Managed by macOS
• Xcode DerivedData5–100 GB · Safe
• Docker disk image10–100 GB · Usually safe

Typical ranges on Macs that have these items at all, from the research behind the app's catalog. Many Macs have far less. Local snapshots aren't shown because their size depends entirely on what changed since each was taken.

How big should System Data be?

There's no normal size. Apple doesn't publish one, and the parts that make it up depend on how you use your Mac. A Mac that backs up with Time Machine, runs Xcode and Docker, and has been in use for years will carry far more than a new one used for mail and browsing.

What's worth noticing is change. A System Data figure that jumps by tens of gigabytes points to one part that grew: usually snapshots, a cache, a virtual machine or a set of models.

Why does System Data change by itself?

Snapshots are taken every hour and age out after a day, swap grows and shrinks with memory use, and caches fill as you work. Storage settings also works its figures out in the background, so a number you read before it settles can move a lot.

A drop overnight usually means snapshots aged out or swap was cleared by a restart. A rise usually means new snapshots holding files you deleted or changed, or an app that downloaded or built something large.

Why is System Data larger after a macOS update?

macOS saves a local snapshot before each update, and like any snapshot it holds on to space until it's removed. Storage settings also needs time to work out its figures again after an update. Give it a day or two, and a restart, before you go looking for anything to remove.

How can you find out what's inside your own System Data?

Storage settings won't tell you. To look for yourself:

1. Check snapshots first: in Disk Utility, choose View › Show APFS Snapshots and select your startup disk's volume.
2. Check swap: in Activity Monitor, click Memory and look at Swap Used.
3. In Finder, choose Go › Go to Folder, enter ~/Library, and use File › Get Info on Caches, Application Support, Containers and Developer to see how large each is.
4. Look at the folders of the tools you use, such as Docker, Xcode, and AI model folders in your home folder.

Folders at the top of the disk, such as /private/var, are hidden in Finder, and macOS keeps parts of them private, so their totals are hard to get by hand.

What not to do with System Data

Advice on System Data is full of shortcuts that cost more than they save. Most of them come from treating it as one pile of files, when it's a dozen different things with different owners.

Don't delete folders macOS manages

Leave /System, /private/var and their contents alone. macOS protects most of it, and manages the rest: swap, temporary files, logs and the Spotlight index all have their own mechanisms, which the sections above describe.

Don't move whole Library folders to the Trash

The Caches, Application Support and Containers folders themselves hold every app's data and settings. Remove single items inside them, after checking what they are, never the folders. The same goes for the Library folder itself.

Don't reinstall macOS to shrink it

Reinstalling macOS doesn't remove your apps, your data or your caches, and System Data comes back from the same snapshots, caches and tools. Erasing the Mac and starting again does clear it, at the cost of setting everything up again, and it grows back the same way.

Don't paste Terminal commands from a web page

Guides that ask you to paste a command to "clear System Data" are ones to close. Commands that delete files can't be undone, and fake cleanup guides are a known way to install malware. Everything in this post works through Finder, System Settings and the apps themselves.

How the app does it

Wombit is a native Mac app that shows what's using your storage, explains every item in plain language, and clears it safely: Trash first, undoable and logged. Its scan reads only names, sizes and dates, and file names and paths never leave your Mac.

System Data, explained splits that one number into named buckets, such as local snapshots, caches, logs, swap and sleep image, app data and developer files, and shows how much it couldn't explain, instead of hiding it in a total. Folders macOS didn't let it read are listed, not skipped, and hard links and APFS clones count once.

Every item comes from a catalog entry written and checked by hand, with sources. Items no rule explains get a Best guess, written on your Mac by Apple Intelligence and labelled as a guess. These are the entries for the parts in this post:

• Time Machine local snapshots

  Hourly snapshots of your startup disk that Time Machine keeps on the disk itself, so you can restore files even without your backup disk.

  Managed by macOS · Runs tmutil for Time Machine's own snapshots, through the helper

• ~/Library/Caches/*

  App caches

  Data that apps and macOS services keep so they can load things faster. Apps create it again when they need it.

  Safe · Moves it to the Trash

• /Library/Caches/*

  Shared app and system caches

  Caches that apps and macOS services keep for every user of this Mac, in the Library folder at the top of your disk.

  Usually safe · Moves it to the Trash

• /private/var/folders

  Per-user temporary files and caches

  Private temporary folders and caches that macOS creates for each user account, in hidden folders with random names.

  Managed by macOS · Explained only: never removed

• /private/var/vm

  Swap files and sleep image

  Disk space macOS uses as extra memory when RAM runs low, and a copy of memory it can save before a long sleep.

  Managed by macOS · Explained only: never removed

• ~/Library/Logs/DiagnosticReports/*

  Crash and diagnostic reports

  Reports macOS saves when an app crashes, stops responding or uses a lot of resources. You can view them in the Console app.

  Safe · Moves it to the Trash

• /System/Volumes/Data/.Spotlight-V100

  Spotlight index

  The index Spotlight keeps for each disk so it can find files, and what's inside them, quickly.

  Managed by macOS · Explained only: the app shows you how

• ~/Library/Application Support/*

  Application Support folders

  Data that apps create and manage for you, such as libraries, databases, downloads and settings, in a folder for each app.

  Review first · Explained only: the app shows you how

Each entry has a level. Safe items, such as app caches and crash reports, start checked in Cleanup, and only they count in the headline number. Usually safe and Review first items wait for you. Managed by macOS items, such as swap and the Spotlight index, are explained and handled through macOS's own mechanism, never moved.

Seeing System Data explained is part of the free analyzer. Cleanup, removing Time Machine snapshots and items that need an administrator, such as shared caches, are PRO: one payment of $4.99 with lifetime access. Every Pro tool's review is free to open, so you see what would go and why before you buy.