What does a differential backup copy?

A differential backup copies all data that has changed since the last full backup was performed. This means that it captures all modifications to files or new files that have been created since that specific full backup. It does not reset after each backup; instead, it continues to accumulate changes until the next full backup occurs. This approach allows for faster recovery times compared to doing a full backup every time, as it reduces the volume of data being processed after the initial full backup.

In contrast, the other options miss the mark in defining what a differential backup entails. For instance, copying only the most recently created files would not account for changes made to existing files since the last full backup. Likewise, including only deleted data misinterprets the function of differential backups, which focus on capturing active files rather than those that have been removed. Lastly, stating that it copies no data and only system settings ignores the primary goal of backing up data for recovery purposes, which is the essence of differential backups.