I think a short explanation of the "archive" attribute of a file is worthy of note. In the explanation of Full, Incremental and Differential backups, how does it know about changes?
I offer that a tangential mention of the ATTRIB of the file...Read, System, Hide & Archive, is worthy. The short story is that the OS just needs to scan files for files where the Archive bit has been set. Except for a full backup, the OS just checks the Archive bit of the files to select which ones are chosen.
My observation is only to thank you for the explanations of other parts of the OS. It's offered in good faith and to the next generation that never knew DOS 2.0<g>