backup what:
what is data files, and what is system files
System Files: Files from the installation source, usually default files put on by the installation media in order for the system to work as intended.
System Settings: setting files for determining the behavior of the system. This would be such things as samba settings, network settings, etc.
Default Settings: System settings that are created as defaults during OS or Application installation.
Data: User data, basically all files and other data that is on a system created or otherwise put there by a user. Movies, songs, documents, and including such things as user profiles or other such data. Basically anything that is on a system for or by the user and is not included by default by installation material.
backup how: