Which backup method saves all changed files since the last full backup?

The method that saves all changed files since the last full backup is the differential backup. This approach captures not only new or modified files but also keeps track of all changes made since the last full backup was completed. This means that you only need to have the last full backup and the most recent differential backup to restore the system to its latest state.

In contrast, a full backup captures all files every time it is performed, resulting in a larger amount of data being stored but providing a complete snapshot of all the data at a specific point in time. An incremental backup, on the other hand, saves only the changes made since the last backup of any kind (either full or incremental), meaning that to restore to the latest state, one would need the last full backup and all subsequent incremental backups. Finally, the term "complete backup" is often used interchangeably with a full backup, further emphasizing that it captures everything without reference to incremental changes.