What determines what is to be backed up?

[Palmadesso Jack]

Good Morning,

What criteria does ADSM use to determine what files are to be backed up
incrementally.  Does it go just by last date modified or by the actual
contents of the file or something else? I have some clients that show they
backed up some files last night that have not been modified since 8/2.  Why
is this happening?

Jack