How NetBackup determines that files are due for backup on Windows

On Windows clients, NetBackup performs the incremental backups of files that are based on the Perform incrementals based on archive bit setting. This setting is found in the Backup, Archive, and Restore client interface, under File > NetBackup Client Properties, on the General tab.

If Perform incrementals based on archive bit is enabled, incremental backups for this client are based on the state of the archive bit of each file. The operating system sets the bit whenever a file changes and it remains set until cleared by NetBackup. The conditions under which NetBackup clears the bit depend on the type of backup being performed.

For a full backup, NetBackup backs up files regardless of the state of their archive bit. After a full backup, the archive bit is always cleared.
For a differential incremental backup, NetBackup backs up the files that have the archive bit set and have therefore changed. When the client receives a response from the server that indicates that the backup was successful (or partially successful) the archive bits are cleared. The clear archive bit lets the next differential incremental back up only the files that changed since the previous full or differential incremental backup.
For a cumulative incremental backup, NetBackup backs up the files that have the archive bit set. However, NetBackup does not clear the archive bits after the backup. Without a clear archive bit, the next cumulative incremental backup backs up changed files and the files that were in the cumulative incremental backup.

If Perform incrementals based on archive bit is disabled, NetBackup includes a file in an incremental backup only if the datetime stamp of the file has changed since the last backup. The datetime stamp indicates when the file was last backed up.

Depending on the timestamp, NetBackup behaves in the following manner:

For a full backup, NetBackup backs up files regardless of the datetime stamp.
For a differential incremental backup, NetBackup compares the datetime stamp of the file against the last full or incremental backup.
For a cumulative incremental backup, NetBackup compares the datetime stamp of the file against the last full backup.

If files are installed or copied from another computer, the new files retain the datetime stamp of the originals. If the original date is before the last backup date, the new files are not backed up until the next full backup.