<operating system> A kind of backup that copies all files that have changed since the last full backup. Each differential backup will include all files in previous differential backups since the full backup so to restore a version of a file, you only need to search the full backup and the relevant differential backup. Some systems support differential backup by associating an "Archive" flag with each file and setting this flag whenever the file is modified to indicate that it should be included in the next backup. A differential backup does not change this flag, whereas an incremental backup resets it. (2004-03-05)

A differential backup is a type of data backup that preserves data, saving only the difference in the data since the last full backup. The rationale in this is that, since changes to data are generally few compared to the entire amount of data in the data repository, the amount of time required to complete the backup will be smaller than if a full backup was performed every time that the organization or data owner wishes to back up changes since the last full backup.

<operating system> ("back up" when used as a verb) A spare copy of a file, file system, or other resource for use in the event of failure or loss of the original. The term commonly refers to a copy of the files on a computer's disks, made periodically and kept on {magnetic tape} or other removable medium (also called a "dump"). This essential precaution is neglected by most new computer users until the first time they experience a disk crash or accidentally delete the only copy of the file they have been working on for the last six months. Ideally the backup copies should be kept at a different site or in a fire safe since, though your hardware may be insured against fire, the data on it is almost certainly neither insured nor easily replaced. See also backup software, differential backup, incremental backup, full backup. Compare archive, source code management. (2004-03-16)