What Is BIOS?

Date First Published: 4th December 2023

Topic: Computer Systems

Subtopic: Computer Software

Article Type: Computer Terms & Definitions

Difficulty: Medium

Difficulty Level: 7/10

CONTENTS

Functions Of The BIOS
Accessing BIOS
History

Learn about what the BIOS is in this article.

Stands for Basic Input/Output system. BIOS, pronounced "bye-oss" is a firmware program stored on a ROM chip on the motherboard that provides a user interface for accessing and setting up the computer at the most basic level. It is made accessible to the microprocessor on an EPROM chip, which passes control to the BIOS program when users turn on their computer.

Every time the computer is powered on, the BIOS is automatically loaded. At first, it will run the boot sequence by scanning for installed hardware components, running the POST checks, locating the boot disk, and loading the operating system.

Functions Of The BIOS

The four main functions of BIOS are:

Power-on self test (POST) - Checks that all hardware is working properly before starting the boot process. Additional information is provided through visual POST codes and beep codes if the computer does not pass the POST to help understand why the computer is failing to boot.
Bootstrap loader - Locates the operating system. The BIOS will pass control to it if a capable operating system is found.
Software/drivers - Locates the software and drivers.
BIOS or CMOS setup - A configuration program that allows hardware and system settings to be configured.

Accessing BIOS

The BIOS interface can be accessed during startup by pressing a keyboard key, often F2 whilst the manufacturer's logo appears on the screen. Accessing the BIOS varies, depending on the computer being used. Once in the BIOS interface, users can change hardware settings, manage memory settings, change the boot order or boot device, change system power settings, and perform other configuration tasks.

History

The term "bios" was invented by Gary Kildal and first appeared in the CP/M operating system in 1975, describing the machine-specific part of CP/M loaded during boot time that interfaces directly with the hardware. (A CP/M machine usually has only a simple bootloader in its ROM.)

The BIOS of the original IBM PC and XT had no interactive user interface. Error codes or messages were displayed on the screen, or a coded series of sounds were generated to signal errors when the power-on self-test (POST) had not proceeded to the point of successfully initialising a video display adapter.