Basic Input Output System

What is the BIOS?

The Basic Input Output System (BIOS), also known as the System BIOS or ROM BIOS, is software that is programmed into and stored on a read only memory (ROM) chip, often referred to as a CMOS chip. This is the first code that executed by a PC when it is powered on. The CMOS chip itself is located on the motherboard of a PC.

What does the BIOS do?

When the PC starts up, the first job for the BIOS is the power-on self-test, which initializes and identifies system devices such as the CPU, RAM, video display card, keyboard and mouse, hard disk drive, optical disc drive and other hardware.

BIOS settings can be altered in the BIOS Setup, which can usually be entered during startup by pressing the DEL or F2 key (keys may vary with manufacturer, refer to your motherboard manual).

The BIOS then locates boot loader software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD/DVD, and loads and executes that software, giving it control of the PC. This process is known as booting, or booting up, which is short for bootstrapping.

Reseting the BIOS.

Most motherboards have a "Restore factory defaults" option in the BIOS setup software which can be selected to return to the settings that the chip was originally shipped with. The motherboard also has a jumper which allows you to return to the default BIOS settings configured by the manufacturer. This is useful when you cannot access the BIOS Setup because of incorrect settings or lost BIOS passwords. Make sure the power is completely off when you short the jumper.

Flashing the BIOS.

Updating, or "flashing" the BIOS, is a procedure that involves rewriting the contents of the CMOS chip and is usually performed by means of a special program provided by the system's manufacturer. This program, sometimes referred to as a "BIOS image", is typically downloaded to the primary hard drive or to the root of a bootable USB flash drive and executed at POST. A BIOS upgrade might be performed to fix existing bugs or provide improved performance. It may also be necessary to support newer hardware, or to repair a damaged BIOS.

Warning: Once it is determined that a BIOS flash is in order and begun, the process should not be interrupted for any reason. Doing so may render the unit inoperable.