What does the Basic Input/Output System (BIOS) do?

The Basic Input/Output System (BIOS) is crucial in the computer's startup process. Its primary role is to contain the routines that are executed when the computer powers on. This includes performing a Power-On Self-Test (POST) to check hardware components such as the keyboard, RAM, and storage devices to ensure they are functioning properly before loading the operating system.

After the POST is completed successfully, the BIOS then locates the operating system's boot loader from the designated storage device and transfers control to it, thus initiating the loading process of the operating system. This foundational role of the BIOS is vital for the overall startup sequence of a computer.

In contrast, executing applications on startup pertains more to operating system-level tasks that occur after the BIOS completes its functions. Acting as a firewall or managing network connections are responsibilities that involve higher-level software or components within the operating system, which come into play after BIOS has performed its initial duties. By understanding that the BIOS is the first layer of software that interacts with hardware upon startup, its critical function becomes clear.