How do UNIX backup programs know which files to dump. Unlike Windows, UNIX files do not have the "archive" bit, yes? So, again, how does it know which file(s) to dump. Thanks in advance.

Unix backup programs typically record the time at the start of a backup. So, for example, you do a level 0 backup at 1:00 am on the first day of the month. Then a level 1 is any file that changed after 1:00 am on the first day of the month. This enables muli-level backups too. You might do a monthly level 0 backup. Then a weekly level 1 backup. And a daily level 2 backup. Then to recover, you need the monthly, the most recent weekly, and the most recent daily backup. But the daily backups do not take a long time at the end of the month. If you change a file during the month, it will tend to be on several weekly and several daily backups...which is a big help is one tape is unreadable. You really can't do stuff like this with just a single archive bit.