What's the difference between backup and sync?

Episode 1225 (51:13)

Jonathan from Pittsburgh, PA

Jonathan is having trouble backing up his Mac. He backs up to one with Time Machine and one with Super Duper. He formatted his hard drive to do a clean install. When he plugs in his backup drive, will it sync and wipe out what he has? Leo says backups will never delete anything from the backup. It just adds to it. Then he can restore to his source drive for that very reason.

Sync, on the other hand, can do just that, but sync software like Super Duper have a feature called "versioning," which keeps different versions of files. But he'd have to be sure he has the right settings for that.