What is the main characteristic of a differential backup?

The main characteristic of a differential backup is that it backs up all changes made since the last full backup. This means that each time a differential backup is executed, it captures all the files that have changed since the most recent full backup, regardless of any previous differential backups. This approach allows for efficient data recovery; if a restoration is needed, you would only require the last full backup and the most recent differential backup.

Differential backups are advantageous because they reduce backup time and storage requirements compared to performing a full backup each time. Unlike incremental backups, which only save changes made since the last backup of any type (whether full or incremental), differential backups simplify the restoration process by minimizing the number of backup files needed.

In contrast, other options do not accurately describe a differential backup's functionality. For instance, backing up all files every time or providing a full copy of all data indicates a full backup scenario, which focuses on capturing the complete dataset rather than just the changes. Optionally backing up changes since the last incremental is specifically characteristic of an incremental backup rather than a differential one.