BIOS, pronounced “BYE-oss,” stands for Basic Input Output System and is software stored on a small memory chip in your system’s motherboard. When you boot up your system and look at the screen at the right time, you may see a startup message that uses the term “BIOS.”
BIOS is the first software that runs when you power on your system, performing an initial pack of diagnostic tests (POST, or Power On Self-Test) to see if there are any issues with the hardware. POST is the first step in your hardware’s boot sequence. The machine won’t continue with the boot sequence if the POST fails.