# System Data Canonical page: https://vitalsmac.com/glossary/system-data Activity Monitor glossary, Figures Activity Monitor leaves out. What is System Data on Mac? Also: Other storage **Short answer:** System Data is the category in the Mac's storage settings for files macOS does not put anywhere else: caches, logs, local Time Machine snapshots, swap files, and the data apps keep in the Library folders. Before macOS Monterey it was called Other. Open System Settings → General → Storage and the bar at the top splits the disk into Applications, Documents, Photos, macOS and a few more. System Data is what is left once those are counted. That is why it can be anything from 10 GB to well over 100 GB, and why the Storage pane cannot list what is in it the way it lists Documents. A large System Data figure is not a fault. Some of it is working space macOS needs, some of it is space macOS will free on its own when the disk runs short, and some of it is data an app keeps and never clears: a virtual machine, a container disk, simulator images, old device backups. The last kind is where the tens of gigabytes usually are, and it is the only kind worth removing by hand. ## What is usually in System Data The contents differ from Mac to Mac, but the same few things account for most of it. - Local Time Machine snapshots, copies of recent changes kept on the startup disk. Often the largest single piece on a laptop. - Swap files and the sleep image, which grow with memory use and shrink after a restart. - Caches and logs, for macOS and for every app. Most are small and rebuilt when deleted. - App data in the Library folders: virtual machine disks, container images, mail downloads, chat app media. - Developer data that Xcode does not claim, such as simulator runtimes and package caches. - Updates macOS has downloaded and not yet installed. ## What is safe to remove, and what is not Safe: data you can name and no longer need. Old iPhone and iPad backups (Finder → the device → Manage Backups), virtual machines you have finished with, container images you can pull again, simulator runtimes you do not test against, and local snapshots once the backup disk has a recent copy. Leave alone: the swap files, the sleep image, and folders under /System, /private/var or /Library that you do not recognize. macOS manages those itself, and deleting them can stop apps or macOS from working until they are rebuilt. Cleaner apps mostly remove caches, which come back within days. The number drops for a while, and the cause stays. ## How to find what is taking the space The Storage pane will not open System Data, but Finder and Terminal can measure the folders it is made of. Start with your own Library, where most app data lives. 1. In Finder, choose Go → Go to Folder, type `~/Library` and press Return. 2. Switch to list view (⌘2), choose View → Show View Options, and turn on Calculate all sizes. Click the Size column to sort by it. Large folders take a moment to fill in. 3. Open the largest folders. Containers, Application Support, Developer and Caches are the usual places, and a folder named after an app tells you which app is holding the space. 4. For a list in Terminal, run `du -sh ~/Library/* 2>/dev/null | sort -h | tail -15`. It prints the 15 largest folders in your Library, biggest last. Some folders are only readable if Terminal has Full Disk Access in System Settings → Privacy & Security. 5. Run `tmutil listlocalsnapshots /` to see the local Time Machine snapshots. Each line is one snapshot, and together they can hold tens of gigabytes. ## The usual large items, and how to remove each Once you know what it is, remove it with the tool that made it, not by dragging its folder to the Trash. The app's own tool knows which files belong together and leaves the rest working. - Old iPhone and iPad backups: in Finder, select the device, click Manage Backups, and delete the ones you do not need. - Local Time Machine snapshots: macOS keeps each one for about a day and deletes them sooner when the disk runs short. To remove one now, use `tmutil deletelocalsnapshots` with the snapshot's date from the list. - Docker: its containers and images live in one disk image. Run `docker system prune` to remove what is not in use, and lower the disk size limit in Docker Desktop's settings. - Xcode simulators: run `xcrun simctl delete unavailable` to remove simulators for runtimes that are no longer installed, and remove runtimes you do not test against in Xcode's settings. - Virtual machines: delete the ones you have finished with from inside the app that runs them, such as Parallels, VMware Fusion or UTM. ## Why the figure changes by itself System Data is not a fixed pile of files. Snapshots come and go with each backup, swap files grow while memory is under pressure and are removed after a restart, and caches fill and empty as you work. The Storage pane also takes a while to recalculate, so the number right after a cleanup can be out of date. Watch it over a few days rather than a few minutes. A figure that goes up and down by 10 GB is macOS doing its job. A figure that only ever climbs points at an app that keeps adding data and never removes it, and the Library folders will show you which one. ## Questions people ask ### What is System Data on a Mac? The part of the storage bar for files macOS does not put in another category: caches, logs, local Time Machine snapshots, swap files and the data apps keep in the Library folders. It was called Other before macOS Monterey. ### Why is System Data so large? Usually because of one or two big items: local Time Machine snapshots, a virtual machine or container disk, simulator runtimes, or old device backups. Caches and logs rarely add up to more than a few gigabytes. ### Can I delete System Data? Not as a whole, and not from the Storage pane. You can remove the large items inside it that you recognize, such as old backups, virtual machines and local snapshots. Leave system folders you do not recognize alone. ### Does restarting the Mac reduce System Data? A little. A restart removes the swap files and some temporary files, which can free several gigabytes on a Mac that has been up for weeks. It does not touch snapshots, backups, virtual machines or app data, which are usually the larger part. ### Why is System Data larger after a macOS update? The update may leave downloaded files, a snapshot taken before it installed, and caches that are rebuilt afterwards. Most of that is cleared by macOS within a few days. If it is not, look for local snapshots with `tmutil listlocalsnapshots /`. ## In Vitals Vitals shows free space per volume on its Disk tab and in the menu bar, and which app is writing to the disk right now. It does not break down System Data or delete anything. ## Related - [Purgeable space](https://vitalsmac.com/glossary/purgeable-space) - [Swap Used](https://vitalsmac.com/glossary/swap-used) - [backupd](https://vitalsmac.com/glossary/backupd) - [Cached Files](https://vitalsmac.com/glossary/cached-files) Looking for something better than Activity Monitor? See [the best Activity Monitor alternatives for Mac](https://vitalsmac.com/best-activity-monitor-alternatives), or [every term in the glossary](https://vitalsmac.com/glossary).