What Is System Data on Mac and iPhone (and How to Reduce It)

Quick answer: System Data is the catch-all storage category for caches, logs, temporary files and other files that macOS or iOS manages itself. You can’t delete it directly. To shrink it, restart, install pending updates and clear browser and app caches. On iPhone, reinstalling apps with heavy caches helps most. On a Mac, so does letting Time Machine clear its local snapshots.

The rest of this guide explains what sits inside System Data on each device, why it jumped after the macOS 27 and iOS 27 updates, and which fixes are safe.

What is System Data on Mac?

Open Apple menu > System Settings, click General, then click Storage. System Data is the category for everything that doesn’t belong to a more specific one, like Applications, Documents or Photos.

Apple’s guide to finding and deleting files on your Mac says it mainly holds files and data used by the system, such as log files, caches, virtual memory (VM) files and other runtime resources. It also includes temporary files, fonts, app support files and plug-ins. Apple is direct about the limits: you can’t manage this category from Storage settings, macOS manages it, and it varies in size with the current state of your Mac.

Two parts of that list are yours to clean: app caches in ~/Library/Caches and app support files in ~/Library/Application Support, including ones left behind by apps you’ve deleted. The rest is the system’s job.

Time Machine local snapshots are the other piece people find here. According to Apple’s page on Time Machine local snapshots, your Mac takes one roughly every hour and keeps it for 24 hours, keeps a snapshot of your last successful backup, and saves another before installing a macOS update. Apple counts that space as available storage and deletes snapshots when the space is needed.

What is System Data on iPhone?

On iPhone, open Settings > General > iPhone Storage. In recent iOS versions, System Data is listed there along with iOS itself.

Apple’s article on checking the storage on your iPhone and iPad still uses the older name, Other. It describes the category as non-removable assets like Siri voices, fonts and dictionaries, non-removable logs and caches, the Spotlight index, and system data such as the Keychain and CloudKit database. The operating system itself is counted separately.

Apple also notes that an app’s cached and temporary data might not count toward that app’s own usage. That’s a likely reason heavy apps add to System Data without showing it on their own line.

You can’t open System Data on an iPhone, and no app can clear it for you. iOS sandboxes every third-party app, so one app can’t reach another app’s files or the system’s. iOS removes cached and temporary files itself when it needs room.

System Data on Mac vs iPhone

Question	Mac	iPhone
Where you see it	System Settings > General > Storage	Settings > General > iPhone Storage
What’s inside	Logs, caches, VM files, temporary files, fonts, app support files, plug-ins	Logs and caches, Siri voices, fonts, dictionaries, Spotlight index, Keychain data
Backup snapshots	Time Machine local snapshots	Not applicable
Can you browse it?	Partly, through ~/Library in Finder	No
Does it clean itself?	Yes, caches, logs and staged updates when space is needed	Yes, cached and temporary files when storage is low
Your best levers	Restart, app caches, snapshots, pending updates	Restart, updates, Safari data, reinstalling heavy apps

Why System Data balloons after a major update

macOS 27 and iOS 27 shipped on September 14, 2026, and plenty of people noticed System Data jump afterward. Several things can contribute:

• Your Mac took a snapshot before installing. Apple says Time Machine saves one before every macOS update. It’s removed later, when it ages out or when space is needed.
• Caches and indexes can rebuild. Apps and the system may recreate caches after an update, and on iPhone the Spotlight index lives in this category.
• New on-device models download. Apple’s page on getting Apple Intelligence lists up to 14GB of storage on models such as iPhone 17 Pro, iPhone Air and Macs with M3 or later and at least 12GB of memory, and up to 8GB on other supported devices. Apple doesn’t say which storage category those files count under.

After the iOS 27 release, some users posted storage screens where iOS, Apple Intelligence and System Data together came close to 70GB. Those are user reports, not Apple figures. In many reports the number fell back after a restart and a few days of normal use, but Apple makes no promise about that.

How to reduce System Data on Mac

1. Restart. VM files and temporary files track what your Mac is doing right now, so a restart is the cheapest first step.
2. Install pending updates. Go to System Settings > General > Software Update. Apple says macOS clears staged macOS and app updates on its own when space is needed, along with logs and interrupted downloads.
3. Clear app caches. Quit the app, open ~/Library/Caches with Go > Go to Folder, and empty the contents of its folder. Our guide to clearing cache on a Mac safely walks through it. BlueHammer Cleaner groups caches by app and shows sizes first, so you can see which apps are worth clearing.
4. Let Time Machine remove local snapshots. Open System Settings > General > Time Machine, click Options, choose Manually from Backup Frequency, then click Done. Wait a few minutes, then switch automatic backups back on.
5. Check snapshots in Terminal if you’re curious. This command lists the local snapshots on your startup disk and changes nothing: tmutil listlocalsnapshots /. Running tmutil deletelocalsnapshots / deletes all of them, and may need sudo and your admin password. It removes only the copies on your Mac, not the backups on your backup disk, but you lose those restore points. The Time Machine settings method above does the same job with less room for a typo.
6. Remove leftovers from deleted apps. Their support files count here. See uninstalling Mac apps completely.
7. Trim Messages. Messages and attachments have their own category, so this frees space without lowering System Data. In Messages, choose Messages > Settings > General and change Keep messages. With Messages in iCloud, deletions apply on all your devices.

How to reduce System Data on iPhone

Be honest with yourself about the goal here. You can’t delete System Data on an iPhone. You can only give iOS a reason to clear what it already manages.

1. Restart. Turn the iPhone off and back on. It deletes nothing you care about, and users often report System Data dropping afterward.
2. Update. Go to Settings > General > Software Update. Apple says your data and settings stay unchanged when you update.
3. Clear Safari data. Go to Settings > Apps > Safari and tap Clear History and Website Data. To keep your history, tap Advanced > Website Data > Remove All Website Data instead. Sites will sign you out. Our guide to clearing cache on iPhone covers other apps too.
4. Offload or reinstall heavy apps. In iPhone Storage, tap an app. Offload App frees the app’s own storage but keeps its documents and data. Delete App removes the app and its data, including its cache. For chat and social apps that cache gigabytes, deleting and reinstalling clears that cache, unless the app has its own clear-cache option. Make sure the app’s data is synced or backed up first.
5. Set Messages retention. Go to Settings > Apps > Messages > Keep Messages and choose 30 days or 1 year. Anything older, attachments included, is removed automatically. Like on the Mac, this frees space under Messages, not System Data.

Last resorts come after all of that. Reset All Settings, under Settings > General > Transfer or Reset iPhone > Reset, returns settings to defaults. Apple says it deletes no data or media, so it isn’t a storage tool. Some users report it helped, but treat that as anecdote. Erasing the iPhone and restoring it from a backup rebuilds everything from scratch, and users commonly report a smaller System Data afterward. Only do it with a backup you’ve checked. If you’re short on space overall, our full iPhone storage guide is the better place to start.

What not to do

• Don’t delete folders in /System, /private or the top-level /Library on a Mac. macOS depends on them, and the payoff is close to zero.
• Don’t run cleanup scripts with sudo rm. One typo in a path can delete far more than a cache.
• Don’t trust an iPhone app that claims to clear System Data. iOS doesn’t let apps reach it. BlueHammer Cleaner on iPhone sticks to what an app can do: finding duplicate, blurry and burst photos and screenshots, which frees space in Photos.
• Don’t erase an iPhone to chase a number. If your device has healthy free space, a large System Data figure isn’t a problem.

When a big System Data number is fine

System Data is meant to move. Caches grow with use, snapshots come and go, and the system trims both when it needs room. A figure that looks alarming the day after an update can be smaller a week later.

The useful test isn’t the size of System Data. It’s whether you have enough free space for what you do. If you do, leave it alone. If you don’t, clear the parts you control, starting with app caches and apps you no longer use.