> Archive bit is somewhat symbolic. It should be set if the file was not archived by the backup utility. Never in my life I have seen the use of this bit.

I have - back in the days of DOS' BACKUP.COM and RESTORE.COM utilities.

I believe the way it worked was that when you created or edited a file, DOS set this bit, and when BACKUP.COM archived it, that cleared the bit again (or was it the other way round?) That allowed you to do a very early form of incremental/differential backup, and had a whole section explaining it in the DOS 3.somethingorother manual I first learnt very basic system administration from.

Back in those days our school PC came like many others with two floppy drives called A: and B: - which is why hard disk names traditionally start at C: - and you backed stuff up with a complicated schedule of put system disk in A:, boot, put data disk in B:, load program then it tells you to swap disks so you take out the system disk and put the backup disk in A: and when you're done you put the system disk back in again.

You could set and clear the archive bit manually with ATTRIB +/-A FILENAME.