In computing, BIOS (/ ˈbaɪɒs, - oʊs /, BY-oss, -⁠ohss; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup).

BIOS, computing, stands for Basic Input/Output System. The BIOS is a computer program embedded on a chip on a computer's motherboard that recognizes and controls various devices that make up the computer. The purpose of the BIOS is to make sure all the things plugged into the computer can work properly.

BIOS, computer program that is typically stored in EPROM and used by the CPU to perform start-up procedures when the computer is turned on. Its two major procedures are determining what peripheral devices (keyboard, mouse, disk drives, printers, video cards, etc.) are available and loading the operating system (OS) into main memory.

Basic input/output system (BIOS) is a type of firmware that usually comes installed on a computer and provides it with instructions to boot up when turned on. Firmware is a form of software or a program embedded in hardware, and in the case of BIOS, it's a memory chip embedded in your motherboard.

The term "BIOS" originated from CP/M, an OS for microcomputers born in 1974. BIOS referred to a program for I/O control in CP/M, which played the role of a device driver today. Unlike PC/AT compatible machines (so-called "PC"), which will be discussed later, the BIOS was stored on a external storage as part of the OS.