The Versioned Backup
A versioned backup (which may also go by any number of other names) contains copies of your files as they existed at multiple points in time. (Time Machine, for example, uses this approach.) If you want to see the version of a file that existed on your Mac two weeks ago, a versioned backup can deliver that—plus today's version and the version that existed a month ago.
Note
As I explained in the Introduction, I've repented of my formerly incorrect practice of referring to versioned backups as "archives." The term archive describes files that have been copied to removable media of some kind for long-term storage and then deleted from the source volume.
A versioned backup starts with a complete copy of a set of files or folders. ...