Time Machine backups are unfussy: unlike many proprietary backup software packages, you can browse a Time Machine backup either through its interface or via the drive in the Finder. However, it appears as if every backup is a complete backup.
This concerned Macworld reader Peter, who just purchased a new iMac and a 4TB external drive to use with Time Machine. “This is going to fill up my external drive fairly quickly,” he worries.
Time Machine just looks like it’s making a full backup every time it creates one, but it’s really using a clever technique to only copy changed files at each hourly interval.
While Time Machine’s method has been the same since its introduction, it’s opaque to most users, because it’s meant to work without requiring any maintenance or fussing. (In fact, that’s a flaw, too, because there are no tools to fix corruption or control any of settings, like frequency and purging of older files.)