Reference

Time Machine

Time Machine is macOS’s built-in backup feature. It copies your files, apps, and system to an external or network drive so you can restore them later, and keeps short-lived local snapshots on the startup disk between backups.

MacmacOS

Time Machine

Also known as: Mac backup, macOS Time Machine, Time Machine backup

Built-in macOS backup to external or network drives
Keeps multiple versions for point-in-time restore
Leaves purgeable local snapshots on the startup disk

What Time Machine does

Set up in Apple menu > System Settings > General > Time Machine, it backs up to a connected external drive or a network volume. Once running, it keeps multiple versions of your files so you can roll back to how things were at a past date.

Between full backups, Time Machine also stores APFS local snapshots on your startup disk. These let you recover recent changes even when the backup drive is not attached.

Time Machine and disk space

A Time Machine backup lives on the backup drive, so it does not free space on your Mac — it is a copy, not a cleanup. The local snapshots it leaves on the startup disk do use space, but macOS treats them as purgeable and removes them automatically when the disk fills.

Related terms

Keep reading the reference.

MacAPFS local snapshotAn APFS local snapshot is a point-in-time copy of your startup disk that Time Machine stores locally so you can restore recent changes even without the backup drive attached. The snapshots temporarily occupy disk space and macOS deletes them automatically when space is needed.macOS Cloud & backupDevice backupA device backup is a copy of your data — apps, settings, messages, and media — saved to the cloud or a computer so you can restore it after a reset, loss, or new device. A backup is a copy, not freed space: it never reduces the storage used on the device itself.General MacPurgeable spacePurgeable space is storage that macOS can reclaim automatically when the disk fills up — mainly caches, regenerable files, and cloud-stored content that has already been uploaded. It still appears used, but macOS frees it on demand rather than failing a write.macOS MacSystem Data (Mac)System Data on a Mac is the catch-all storage category for caches, logs, temporary files, fonts, virtual memory, and APFS local snapshots that do not fit Apps, Photos, or Documents. Much of it is reclaimable cache that macOS manages and purges on its own as space runs low.macOS

Act on it

Guides and tools for this topic.

Mac Storage Full: What’s Safe to Delete