What is BIOS?

BIOS:-

Your system’s BIOS (Basic Input/Output System) is firmware stored in a chip on your PC that handles basic system startup—in essence, it gets your computer’s hardware ready so that the operating system can load on it. What’s important to understand about the BIOS is that it runs before Windows runs, and handles the basic tasks of recognizing and configuring your hardware.
And here is the rest of it.