When does the functionality of BIOS take place during a computer's operation?

The functionality of the BIOS (Basic Input/Output System) occurs during the startup process of a computer. When the computer is powered on, the BIOS is the first piece of software that runs. Its primary role is to conduct a Power-On Self-Test (POST) to check the hardware components, ensuring everything is functioning correctly before the operating system loads. Additionally, the BIOS is responsible for initializing hardware and helping to load the operating system from storage into memory.

While the operating system is running, applications are being loaded, or when the system is powered down, the BIOS is not active. Its operations are specifically confined to the initial startup phase, making the identification of this period crucial to understanding how computers boot up and how hardware interacts with software at the most fundamental level.