BIOS
Basic Input Output System
A program that runs the moment you turn on a computer, preparing its hardware components to start working.
In Simple Terms
BIOS is the program that runs first when you power on a computer, getting parts like the keyboard and screen ready to work. When you press the power button, BIOS first checks that components like the motherboard and memory are working correctly. After that, it calls up the startup program (the bootloader) stored on the SSD or HDD.
Behind the Name
BIOS stands for Basic Input/Output System: Basic (fundamental), Input Output (the flow of data in and out), and System (a mechanism). It's named this way because it's the most basic program a computer relies on, kicking in the moment it's powered on.
Take a Closer Look!
BIOS is the program that runs first, the instant you power on a computer, initializing each hardware component and starting the process of booting the operating system. It handles the most basic input and output — things like the screen display and keyboard — and lives on a dedicated chip on the computer's motherboard.
Simply put, BIOS gets everything ready before a computer can run. After you press the power button and power reaches every component, BIOS checks each one in turn — the CPU, memory, storage, and more — to confirm it's working normally. Once the checks pass, BIOS calls up the startup program (the bootloader) at the start of the SSD or HDD and hands off control to it. The bootloader then loads the OS itself, such as Windows, and passes control of the computer to it.
BIOS also opens a settings screen where you can set the date and time or change which storage device boots first. This describes the traditional firmware known as BIOS. UEFI was created to replace it, using a different method for finding and handing off to the OS. Because it still follows the same basic role — checking hardware after power-on, then handing control to the OS — UEFI's settings screen is sometimes still referred to as "BIOS settings" out of habit.