The BIOS, or Basic Input/Output System, is a low-level software that is installed on a computer's motherboard. It acts as a bridge between the computer's hardware and the operating system. The BIOS performs a power-on self-test (POST) when the computer is first started, and initializes and identifies system components, such as the CPU, memory, and hard drive.
Additionally, the BIOS provides a user-configurable setup utility that allows you to change system settings, such as the time and date, the boot order of devices, and system security options. The BIOS also provides an interface for accessing and controlling certain hardware devices, such as the keyboard and mouse.
In modern computers, the BIOS has largely been replaced by the Unified Extensible Firmware Interface (UEFI), which provides more advanced features and capabilities compared to the traditional BIOS.