What is the purpose of the Internet Recovery startup?

The Internet Recovery startup is specifically designed to allow a Mac to recover the operating system by downloading it over a broadband internet connection. This feature is particularly useful in scenarios where the existing operating system has been corrupted, or if the recovery partition on the Mac is no longer available due to disk issues. When a user initiates Internet Recovery, the Mac can connect to Apple's servers and download the latest appropriate version of macOS for that hardware model, enabling the user to reinstall the operating system even without a local recovery partition.

The other options describe functionalities that are not related to the Internet Recovery feature. For example, booting from external drives is a separate process that allows users to start up their Mac from an external device, while local backups pertain to saving data to an external drive using Time Machine or similar tools. Resetting a firmware password involves a different process that is unrelated to the operation of Internet Recovery. Thus, the purpose of Internet Recovery is specifically tailored to restoring or reinstalling the operating system via an internet connection.