System Data is the catch-all category macOS uses for every Apple and third-party file that does not belong to a more specific category such as Applications, Photos, or Documents, which in practice means log files, caches, virtual memory files, temporary files, fonts, app support files, and plug-ins. Apple’s position is direct: the contents of this category are managed by macOS and cannot be managed by you item by item, and its size changes depending on the current state of your Mac. That does not leave you helpless, because most of what inflates System Data is reachable through documented settings rather than through manual deletion in hidden folders.
What macOS Counts as System Data
Storage settings divide your startup disk into named buckets: Applications, Documents, iCloud Drive, iOS files, TV, Music, Books, Podcasts, Mail, Messages, Music Creation, Photos, Trash, Other Users and Shared, macOS, and System Data. The macOS bucket is the operating system itself. System Data, which older macOS versions labeled Other, is everything left over.
According to Apple’s own description, System Data primarily holds files and data used by the system, such as log files, caches, virtual memory files, and other runtime system resources. It also includes temporary files, fonts, app support files, and plug-ins. Two consequences follow from that definition, and they explain almost every confusing case:
- App support data counts here. When an application stores a large working set outside your Documents folder, for example a mail download cache, a sync database, a virtual machine disk image, or a developer tool cache, that data often lands in an app support folder and is therefore tallied as System Data rather than under the app itself.
- Caches are designed to grow and shrink. macOS creates cache and temporary files on demand and removes them when space is needed, so a large System Data figure on a disk that is otherwise healthy is not automatically a defect.
There is also a measurement wrinkle. Available storage space includes both genuinely free space and purgeable disk caches, which means disk space can be reported as used and available at the same time. Time Machine local snapshots behave the same way: your Mac counts the space used by snapshots as available storage, and snapshots do not consume the space needed for downloading files, copying files, or installing software.
How to Check the Number Before You Delete Anything
Open the storage overview first and let it finish calculating. On macOS Ventura 13 and later, choose Apple menu, then System Settings, click General in the sidebar, then click Storage. On macOS Monterey 12 and earlier, choose Apple menu, then About This Mac, then click the Storage tab.
Three things are worth doing in that pane before you touch a single file:
- Wait, then restart, then look again. The category is recalculated as macOS releases caches, so a figure captured during a large download or an ongoing backup is not a stable baseline.
- Use the information buttons. Categories including Applications, Documents, Messages, Music Creation, Podcasts, Trash, and TV expose a detail view with individual items and sizes. The Documents detail view also offers a file browser that shows the contents and storage used by various folders, and lets you sort by Name, Kind, Last Accessed, or Size, then delete a selected file or reveal it in the Finder.
- Read the difference between total used and the sum of the named categories. If your named categories account for most of the disk and System Data is a few GB, nothing is wrong. If System Data alone is dozens of GB, the steps below have somewhere to work.
If your disk is partitioned, the recommendations shown in Storage settings apply only to the partition that contains your home directory.
Back Up First, and Know Which Steps Cannot Be Undone
Make a complete Time Machine backup to an external disk before you delete anything in this article. This matters more than usual here, because several of the effective steps remove data with no recovery path and no Trash to fish it back out of.
Treat the following as irreversible once confirmed:
- Emptying the Trash. Storage space does not become available until the Trash is emptied, and at that moment the files are gone.
- Deleting a device backup. Removing an iPhone or iPad backup deletes the only local copy of that snapshot of the device.
- Deleting a user account. The account’s home folder and everything in it goes with it.
- Removing a Photos or media library. Local originals that were never uploaded anywhere cannot be recovered.
- Deleting Time Machine local snapshots. The hourly restore points on the internal disk disappear immediately.
- Manually removing files from the Library folder, the virtual memory folder, or system directories. There is no undo, and nothing warns you that an app depended on what you deleted.
Local snapshots are not a substitute for a backup. They live on the same disk as the data they protect and macOS deletes them automatically as they age or as space is needed.
Every Fix, Ranked by Space Returned
The table is ordered by how much space each step typically returns on a Mac where System Data has grown unusually large. Space figures depend entirely on your own usage, so the column describes what the number is tied to rather than promising a fixed amount.
| Fix | Space returned | Hands-on time | Reversible | Recurs automatically |
|---|---|---|---|---|
| Delete old iPhone and iPad backups | Full size of each stored backup, often 10 to 60 GB per device | About 5 minutes | No | No |
| Release Time Machine local snapshots | Up to the combined size of 24 hours of hourly snapshots plus the last backup snapshot | About 10 minutes, plus a few minutes of waiting | No | Yes, snapshots are recreated hourly |
| Turn on Store in iCloud and Optimize Mac Storage | Up to the size of your original photos, videos, and rarely used documents | 5 minutes to set, hours to sync | Yes, originals can be downloaded again | Yes, ongoing |
| Empty the Trash | Exact size of the Trash category in Storage settings | Under 1 minute | No | Optional, auto-empty after 30 days |
| Restart, then start up in safe mode | Size of the system caches macOS clears, usually a few GB | 5 to 10 minutes | Yes, caches are recreated as needed | Yes, on every safe mode boot |
| Set Messages to keep messages for 30 days or 1 year | Size of stored conversations and their attachments | About 2 minutes | 30 days in Recently Deleted, then permanent | Yes, ongoing |
| Erase junk and deleted mail in Mail | Size of junk and deleted mailboxes | About 2 minutes | No | No |
| Delete unused apps and downloaded media | Size of each app or downloaded title | 5 to 15 minutes | Yes, they can be installed or downloaded again | No |
Restart, Then Try Safe Mode
A plain restart releases memory pressure and lets macOS clean up temporary files. If that is not enough, Apple’s documented trick is to start up in safe mode, which clears certain system caches that are then recreated as needed. This is explicitly a temporary measure: it can free enough room to finish a task that needs space while the task is underway, such as installing a macOS update.
On a Mac with Apple silicon, shut down completely, then press and hold the power button until Loading startup options appears, select your startup volume, then press and hold the Shift key and click Continue in Safe Mode. On an Intel-based Mac, turn on or restart the Mac and immediately press and hold the Shift key until the login window appears. You will see Safe Boot in the menu bar. To check which type you have, open About This Mac: an item labeled Chip means Apple silicon, an item labeled Processor with an Intel processor name means Intel. Restart normally afterward.
Remove Old iPhone and iPad Backups
Local device backups are frequently the single largest recoverable block on a Mac, and they accumulate silently across devices you no longer own. Connect the device with a cable, open a Finder window, select the device in the sidebar, trust the device if prompted, open the General tab, then click Manage Backups to see the list. Control-click the backup you want to remove, choose Delete, then confirm.
Backups are stored in the home Library folder, at Library/Application Support/MobileSync/Backup, reachable through the Finder Go menu, then Go to Folder. Use that path to look, not to edit. Do not rename, relocate, or extract individual files inside a backup folder, because a backup that has been altered may no longer restore. Deleting a backup is permanent unless you copied the backup folder to another disk first.
Release Time Machine Local Snapshots
Time Machine saves one snapshot of your startup disk approximately every hour and keeps it for 24 hours, and keeps an additional snapshot of your last successful Time Machine backup until space is needed. Snapshots are stored only on disks with plenty of free space and are deleted automatically as they age, so in most situations this step is unnecessary.
To clear them deliberately, turn automatic backups off temporarily. On macOS Ventura 13 and later, choose Apple menu, System Settings, General, then Time Machine, click Options, choose Manually from the Back up frequency menu, then click Done. On macOS Monterey 12 and earlier, open System Preferences, then Time Machine, and deselect Back Up Automatically. Wait a few minutes to allow local snapshots to be deleted, then turn automatic backups on again. The deleted snapshots are gone, so if you have been relying on hourly restore points, make an external Time Machine backup before you do this.
Turn On the Built-In Storage Recommendations
Storage settings offers recommendations that are the supported way to keep the disk from filling again:
- Store in iCloud turns on iCloud Drive and stores most files in iCloud, saving local storage space. Files are downloaded on demand, and recent files stay on the Mac.
- Optimize Storage automatically removes movies and TV shows you have already watched from your Mac.
- Empty Trash automatically sets your Mac to remove files that have been in the Trash for more than 30 days.
Two app-level settings belong in the same pass. In Photos, choose Photos, then Settings, click iCloud, select iCloud Photos, then select Optimize Mac Storage, which keeps smaller versions locally and full-size originals in iCloud; Download Originals to this Mac reverses it. In Messages, choose Messages, then Settings, click General, and set the Keep messages menu to 30 days or 1 year, which removes older conversations including all attachments once the period elapses. Deleted messages and attachments sit in Recently Deleted for 30 days before they are permanently removed. In Mail, choose Mailbox, then Erase Junk Mail, and Mailbox, then Erase Deleted Items.
When System Data Stays Large Anyway
Sometimes the number refuses to drop, and that is often correct behavior rather than a problem to fight.
Do not delete cache files, virtual memory files, or system folders by hand. macOS creates and removes those files itself, they are recreated immediately after deletion, and removing the wrong item can break an application or destroy its data with no recovery path. Nothing in Apple’s documentation asks you to empty Library folders manually, and Apple does not document any third-party cleaning utility as part of this workflow, so treat any tool that promises to purge System Data as unsupported and as a risk you are accepting yourself.
If System Data is still tens of GB after the steps above, look for large app support data rather than for a macOS defect. Virtual machine disk images, container and developer tool caches, media production scratch files, and mail download caches all live in app support locations and are counted in this category. The Documents file browser in Storage settings will show you which folders hold the weight, and the right fix is usually the application’s own cleanup or preference setting, not a deletion in the Finder.
Finally, remember the measurement caveats. Purgeable caches and local snapshots are reported as available space, so the free space number can be healthier than the used number suggests. If your only goal is to finish a macOS update on a tight disk, the safe mode cache clear is the documented shortcut and you do not need to delete anything permanently.
Mac System Data FAQ
Is it safe to delete System Data files manually?
No, not as a routine step. Apple states that the contents of this category are managed by macOS and that you cannot manage them directly. Cache and temporary files are recreated on demand, so manual deletion tends to return the space only briefly while risking app data that sits in the same folders with no undo and no Trash. Work through Storage settings, device backups, and app-level settings instead.
Why does System Data grow back after I clear it?
Because most of what it contains is meant to be rebuilt. Log files, caches, virtual memory files, and runtime system resources are created as the system works, and macOS clears the ones that are safe to delete when space is actually needed, including temporary database files, interrupted downloads, staged macOS and app updates, and Safari website data. A figure that rises during heavy use and falls again later is normal.
Does restarting my Mac reduce System Data?
Often, yes, at least temporarily. A restart releases temporary files and memory-related data, and starting up in safe mode goes further by clearing certain system caches, which is Apple’s documented way to free enough room for a task such as installing a macOS update. The effect is short-lived by design, so use it to get unstuck, then apply the durable fixes such as removing old device backups and turning on the storage recommendations.
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