Term: differential backup

A differential backup includes all files changed since the first full backup of a series. The term derives from the word “difference,” in that only the difference of the entire collection of files will be included.

Differential backups are used in conjunction with full backups as space-saving alternatives to backing up everything every time.

A differential backup is used when backups are taken periodically. The first is a full backup of everything. Each subsequent differential backup in the series, backing up all files modified since the first backup. This is in contrast to an “incremental” backup, which includes only those files changed since the immediately preceding backup.

While differential backups save space, they have a built-in dependency: to recover an entire collection of files to its most recent state, the initial full backup must also be available.