Final answer:
An Incremental backup system saves only the files that have changed since the last backup, making it efficient in terms of storage and time. (option B)
Step-by-step explanation:
The backup system that backs up only the files that have changed since the last backup is known as an Incremental backup. This type of backup method is efficient because it only saves the data that has been altered after a full backup or the most recent incremental backup, thus reducing the amount of time and storage space required. Unlike a full backup that copies all files or a differential backup that copies all changes made since the last full backup, an incremental backup will save only those files that were changed or newly created since the last incremental backup.
Full backup (Option A) backs up all selected files regardless of whether they have changed, leading to larger storage requirements and longer backup times.
Incremental backup (Option B) focuses on the changes since the last backup, resulting in smaller and faster backup operations.
Differential backup (Option C) backs up all changes since the last full backup, potentially leading to larger backups compared to incremental backups.
Backup server (Option D) refers to a system or device that manages and facilitates backups but doesn't specify the type of backup strategy.