What “Other” and “System Data” Storage Actually Contains on Your Mac

You open System Settings, check your Mac’s storage, and discover that a huge amount of space is being used by something called System Data.

On older versions of macOS, you may have seen a similarly vague category labelled Other.

Unlike clearly defined categories such as Applications, Photos and Documents, System Data does not immediately tell you what is taking up the space. In some cases, it can occupy tens or even hundreds of gigabytes.

So, what does System Data actually contain, why does it sometimes become so large, and is it safe to delete?

What Is System Data on a Mac?

System Data is a broad storage category used by macOS for files that do not fit neatly into the usual groups.

It can include:

• System files
• Temporary files
• Application caches
• Browser caches
• Log files
• macOS update files
• Local Time Machine snapshots
• Virtual memory files
• App support data
• Plug-ins and extensions
• Fonts
• Email attachments
• iPhone and iPad backups
• Disk images
• Archive files
• Leftover files from deleted applications

Some of this data is essential for your Mac to work correctly. Other files are temporary and may be removed automatically when macOS needs more space.

The difficulty is that macOS often combines all of these items into one large category.

Is “Other” the Same as “System Data”?

Broadly speaking, yes.

Apple used the term Other in older versions of macOS. Newer versions generally use System Data.

The name has changed, but the purpose is similar: it groups together files that macOS cannot easily classify as photos, music, apps, documents or another standard storage type.

This means System Data is not one folder that you can simply open and empty.

It is a collection of files stored across different areas of your Mac.

Why Is System Data So Large?

System Data can grow for several reasons.

A relatively small amount is normal. However, if the figure becomes unusually large, it may be caused by accumulated caches, backups, snapshots or outdated files.

Application Caches

Applications create cache files to help them open and run more quickly.

For example, browsers may cache website images, while video editing software may store previews and temporary render files.

Caches are normally harmless, but they can build up over time.

Some applications are better than others at clearing old cache files automatically.

Browser Data

Web browsers can store:

• Cached images
• Website data
• Cookies
• Download history
• Temporary internet files
• Extensions and plug-in data

If you use several browsers or keep hundreds of tabs open, browser data can become surprisingly large.

Local Time Machine Snapshots

When Time Machine is enabled, macOS may create temporary local snapshots on your internal drive.

These snapshots allow you to recover recently changed or deleted files even when your external backup drive is not connected.

macOS should remove them automatically when storage space is needed. However, they can temporarily make System Data appear much larger.

iPhone and iPad Backups

If you back up an iPhone or iPad to your Mac, those backups may be included within System Data.

A single device backup can take up many gigabytes, especially if it contains photographs, messages, application data and videos.

Old backups from devices you no longer use may remain on the Mac unless you remove them manually.

Email Attachments

Apple Mail and other email applications may download local copies of attachments.

Over several years, this can include thousands of:

• PDF documents
• Images
• Spreadsheets
• Videos
• ZIP files
• Scanned documents

Even after an email is deleted, cached copies may sometimes remain for a period.

macOS Update Files

macOS may download update files before installation.

Incomplete downloads, failed upgrades or previous installation files can occasionally remain behind and consume storage.

Normally, macOS manages these files automatically, but problems can occur after an interrupted or unsuccessful update.

Log and Diagnostic Files

Your Mac keeps logs to record system activity, application crashes and technical errors.

These files are useful for troubleshooting, but they can grow if an application repeatedly crashes or produces excessive diagnostic information.

Virtual Memory and Sleep Files

When your Mac runs low on physical memory, macOS temporarily uses part of the storage drive as virtual memory.

This is known as swap space.

The system may also store information needed for sleep and power-management functions.

These files can grow when:

• Too many applications are open
• The Mac has limited memory
• A particular application uses excessive resources
• The Mac has not been restarted for a long time

They are normally managed automatically and should not be deleted manually.

Application Support Files

Applications often store important data outside the main application itself.

This can include:

• Settings
• Templates
• Project files
• Game data
• Downloaded content
• Databases
• Add-ons
• Device drivers
• Licence information

Deleting an application from the Applications folder does not always remove all of its related support files.

These leftovers can accumulate over time.

Old Disk Images and Archives

Files such as .dmg, .zip, .pkg and other installation archives can sometimes be counted as System Data.

Users often download an installer, install the application and then forget to remove the original installation file.

One installer may not matter, but years of accumulated downloads can use a considerable amount of space.

Is System Data a Virus?

A large System Data category does not automatically mean your Mac has malware.

In most cases, the storage is made up of legitimate system files, caches, backups and application data.

However, unwanted software can sometimes create:

• Large temporary files
• Excessive logs
• Hidden downloads
• Browser extensions
• Cryptocurrency-mining data
• Persistent application support files

If System Data suddenly increases alongside pop-ups, poor performance, overheating or unfamiliar applications, it is worth carrying out a security check.

Why Does the Storage Figure Keep Changing?

The macOS storage screen does not always update immediately.

Your Mac must scan and categorise thousands of files. During this process, the System Data figure may rise, fall or appear inaccurate.

The total can also change because macOS regularly:

• Clears temporary files
• Creates and removes snapshots
• Rebuilds indexes
• Downloads updates
• Manages virtual memory
• Recalculates file categories

Restarting the Mac and allowing the storage screen time to recalculate may produce a more accurate figure.

How Much System Data Is Normal?

There is no single correct figure because every Mac is different.

A Mac used mainly for email and web browsing will usually have less System Data than one used for software development, video editing, music production or managing several mobile devices.

The more important questions are:

• Is the category growing rapidly?
• Is your Mac running out of space?
• Has performance become noticeably worse?
• Is there data from old applications or devices that you no longer need?

If your Mac has plenty of available space and works normally, a moderately large System Data category may not require any action.

How to Reduce System Data Safely

You should avoid deleting files from system folders unless you understand exactly what they do.

Removing the wrong file can cause applications to stop working or make macOS unstable.

Safer steps include the following.

Restart Your Mac

A restart can clear temporary files, reduce virtual memory usage and allow macOS to remove data that is no longer required.

It also forces some applications to close properly rather than continuing to hold temporary files.

Install macOS and Application Updates

Updates may fix bugs that cause applications to create excessive cache or log files.

Keeping macOS updated also improves security and storage management.

Check the Downloads Folder

Look for old installers, disk images, video files and archives that are no longer required.

Sort the folder by size to identify the largest items quickly.

Remove Unused Applications Properly

Dragging an application to the Bin may leave support files behind.

Check whether the software includes its own uninstaller, especially for:

• Antivirus software
• VPN clients
• Creative applications
• Printer software
• Audio tools
• Business software

Dedicated uninstallers are often better at removing related files.

Review iPhone and iPad Backups

Check whether your Mac contains backups from older devices.

Only remove a backup when you are confident it is no longer needed and you have another reliable copy of important data.

Clear Browser Data

Most browsers allow you to clear cached files without deleting saved passwords or bookmarks.

Review the available options carefully before confirming the deletion.

Review Large Email Attachments

Deleting old messages with large attachments may free up space, although changes may not appear immediately.

Make sure important attachments have been saved somewhere secure before removing them.

Empty the Bin

Files placed in the Bin still use storage until the Bin is emptied.

Check the contents before deleting them permanently.

Connect Your Time Machine Drive

If local snapshots are occupying space, connecting your normal Time Machine backup drive may allow macOS to complete a backup and manage those snapshots.

Avoid using Terminal commands to delete snapshots unless you know exactly what you are doing.

Should You Use a Mac Cleaner Application?

Mac cleaner applications often promise to remove System Data with a single click.

Some reputable tools can help identify large files, old caches and unused applications. However, others may exaggerate problems, display alarming warnings or delete more than you intended.

Before using any cleaner application:

• Check that the developer is reputable
• Read the deletion list carefully
• Avoid tools that claim your Mac is “critically infected” without evidence
• Back up your data first
• Never grant unnecessary permissions
• Do not allow an application to remove system files automatically

A storage analyser that shows you where the space is being used is often safer than a tool that automatically deletes everything it considers unnecessary.

Files You Should Not Delete Manually

Be extremely cautious around folders such as:

• /System
• /Library
• Hidden macOS folders
• Virtual memory locations
• System extension folders
• Recovery files
• Unknown files inside application support folders

A file may look unnecessary but still be required by macOS or an important application.

Searching for the largest folder and deleting it is not a safe storage strategy.

Could a Full Drive Slow Down Your Mac?

Yes.

macOS needs free storage for:

• Temporary files
• Software updates
• Virtual memory
• Application caches
• File indexing
• System maintenance

When the drive becomes nearly full, you may experience:

• Slow application launches
• The spinning beachball
• Failed updates
• Freezing
• Application crashes
• Problems saving files
• Time Machine errors
• Poor overall performance

Keeping a reasonable amount of free space gives macOS room to work efficiently.

When Should You Ask for Professional Help?

Professional support is recommended when:

• System Data takes up an unusually large percentage of the drive
• The storage returns immediately after files are deleted
• Your Mac reports that the disk is full
• You cannot identify what is using the space
• Applications are repeatedly crashing
• macOS updates will not install
• You suspect malware
• The Mac contains important business data
• You do not have a reliable backup

A technician can inspect storage usage properly without deleting essential files or putting your data at unnecessary risk.

How Hamilton Group Can Help

System Data can be confusing because it is not a single type of file and there is no universal button that safely removes it.

Hamilton Group can help identify what is using your Mac’s storage, remove unnecessary files safely and resolve the underlying cause of excessive storage use.

We can assist with:

• Mac storage analysis
• Performance problems
• macOS update issues
• Secure data backups
• Malware and security checks
• Application removal
• Time Machine configuration
• Business Mac management
• Ongoing IT support

Before making major changes, we can also ensure your important data is backed up and protected.

To arrange help with a slow or full Mac, contact Hamilton Group on 0330 043 0069 and speak to one of our IT experts.