Time Machine is the backup mechanism of macOS, the desktop operating system developed by Apple.
Time Machine was revamped in macOS 11 Big Sur to support APFS, thereby enabling "faster, more compact, and more reliable backups" than were possible previously.
[5] Time Machine was overhauled in macOS 11 Big Sur to utilize APFS, Apple's modern file system first introduced in 2016.
"[1] There is no option to convert existing, HFS+-based backups to APFS; instead, users who want to benefit from the advantages of the new, APFS-based implementation of Time Machine need to start with a fresh volume.
[2] Time Machine's user interface when retrieving a file uses Apple's Core Animation API.
When toggling through the previous snapshots, the stacked windows extend backwards, giving the impression of flying through a "time tunnel."
Sparse bundles are mounted by macOS like any other device, presenting their content as a HFS+ formatted volume, functionally similar to a local storage.
The only officially supported configurations are:[8] On a Time Capsule, the backup data is stored in an HFS+ disk image and accessed via Apple Filing Protocol.
Although it is not officially supported, users and manufacturers have also configured FreeBSD and Linux servers and network-attached storage systems to serve Time Machine-enabled Macs.
[17] Multiple linking of directories is a peculiar feature for HFS+, and is not supported on modern Unix file systems including Apple's own APFS.
In other words, a hard drive can be restored from a Time Machine backup in the event of a catastrophic crash.
OS X Mountain Lion introduced the ability to use multiple volumes simultaneously for Time Machine operations.