incremental backups

A type of backup operation in which files on your computer are only appended to the backup if they have changed since the previous backup. This accomplishes two things:

• Backups can occur in a fraction of the time, since the entire body of data being protected doesn't have to be transferred and stored every night (assuming nightly backups, which are common).
• You end up with a chronological record of the data being protected (because you can restore your data to the state it was in at any particular incremental backup), which gives you significantly more comprehensive protection.

• In order to efficiently perform incremental backups, your backup software must maintain a detailed (read: often large) index of everything stored to your backup media. Sometimes these catalogs are lost (along with everything else) in the event of a catastrophe. Upside: the index can always be reconstructed as long as you still have the tapes.
• It can take much longer to restore data from an incremental backup as the set of backup media increases in size, since rather than reading back a contiguous block of backup data for a given restore, the backup software must skip through each tape (if you used tapes, for instance) to assemble the most current set of your files available.