The BIOS is software that interfaces hardware components with the operating system. It loads at startup and performs checks before initializing devices and passing control to the operating system. The BIOS locates bootable devices, runs self-tests, displays system settings, and provides drivers for basic input/output. It has been largely replaced by UEFI which is meant to improve on the BIOS and interface directly with Windows.

1. 1
BIOS – Basic Input Output System
• The BIOS is special software that interfaces the major hardware
components of your computer with the operating system.
• BIOS is the interface between hardware and software allowing them to
communicate with each other.
• It is usually stored on a Flash memory chip on the motherboard, but
sometimes the chip is another type of ROM.
• Its most important role is to load the operating system.
• When a system boots its BIOS that runs the system until the operating
system loads and takes control.
• In 2003 Intel introduced UEFI. UEFI (Unified Extensible Firmware
Interface) is meant to completely replace BIOS.
• UEFI is actually another small operating system that interfaces between
the hardware and Windows.
When you turn on your computer, the BIOS does several things. This is its usual
sequence:
1. Check the CMOS Setup for custom settings
2. Load the interrupt handlers and device drivers
3. Initialize registers and power management
4. Perform the power-on self-test (POST)
5. Display system settings
6. Determine which devices are bootable
7. Initiate the bootstrap sequence

2. 2

3. 3
BIOS preforms three basic tasks:
1. It contains the POST program (Power On Self Test) run by the CPU for the
self-test during boot up, and helps to locate and load the operating system.
2. It displays the CMOS Setup screen which is used to configure system
parameters that can be changed.
3. Provides low level drivers for devices such as floppy drives, keyboards, etc
…