The Basic Input/Output System (BIOS) is firmware stored on a small memory chip on a computer's motherboard. BIOS initializes and tests the system hardware components and loads the operating system during the startup process. When the computer is powered on, BIOS performs the POST (Power-On Self-Test) to ensure that all hardware, such as the processor, memory, and storage, is functioning properly. Once the hardware check is complete, BIOS locates the boot loader and passes control to the operating system. Modern systems use UEFI (Unified Extensible Firmware Interface), which offers more advanced features than traditional BIOS.