“Apple’s Time Machine is effectively a well-integrated back-up
utility. The incremental back-ups aren’t done at the lowest level
of Apple’s HFS+ file-system, but is basically done by copying files
on an hourly basis from the source hard drive to the remote
destination.“Each time that’s done, a new copy is made unless the file
contents are unchanged, in which case a hard link between the
versions is created. These hourly backups then turn to daily and
weekly backups until out of disk space or opting to remove the
older data.”