Cmd.exe - Attrib ?

I'm studying for my A+, and in Mike Meyers book for 'Attributes', it mentions that when you run attrib and you notice, 'A' this is an archive.

This is how his book says this:

The archive attribute, which is used by backup software to identify files that have been changed since their last backup.

Well the thing is, I've never used any backup software, so I'm at a loss to understand what is going on here, or maybe I'm not understanding this properly, but it sure looks like what he is saying is if you made a backup then this file is marked as an archive, simple enough, BUT how do I have files listed as archives when I've never made any backups before, this I don't get?

THANKS

 

Certain software can check if the attribute flag is on or off on all files, namely dos commands. If you set the attribute on +a you can specify in the commands to just include the files that have the archive set. Also when a file gets modified it turns on the archive flag so when the backup is run, just the changed files can be backed up and not all the files as they still unchanged making smaller backups. You might want to just copy some fiiles from a folder that have the archive set using xcopy and not all the files in the folder.