The BIOS (Basic Input Output System) is a microchip which contains the software (firmware) for the motherboard. When the computer is switched on, the CPU needs somewhere to get the first instruction from. The BIOS performs the following actions:
1. Checks the CMOS Setup for custom settings
The BIOS configuration is stored in the CMOS microchip. When you change something in the BIOS (for example the boot order) these changes are stored on the CMOS microchip. The master boot record location is stored in the CMOS microchip. CMOS stands for Complementary metal–oxide–semiconductor and is a small amount of RAM which is always powered by a battery.
2. Load the interrupt handlers and device drivers
Interrupt handlers are small pieces of software that act as translators between the hardware components and the operating system. For example, when you press a key on your keyboard, the signal is sent to the keyboard interrupt handler, which tells the CPU what it is and passes it on to the operating system. The device drivers are other pieces of software that identify the base hardware components such as keyboard, mouse, hard drive and floppy drive.
3. Perform the power-on self-test (POST)
The POST tests the hardware devices which are connected to the motherboard such as the CPU, RAM video card, hard drive and keyboard to ensure they are functioning correctly. If any are not functioning correctly the BIOS will alert the user by a series of lights or beeps known as BIOS codes.
Display system settings
Determine which devices are bootable
Initiate the bootstrap sequence
The BIOS knows what type of hardware is connected to the motherboard (eg keyboard, CPU) and how to interact with them. It has the first set of instructions that the CPU (Central Processing Unit) needs in order to find the master boot record.
This chip is either ROM or Flash memory so is not lost when the power is diconnected from the computer.
To obtain the BIOS version you can either see it when the computer first boots up or by running the windows utility msinfo32.exe and looking under the summary screen.
Upgrading the BIOS
Upgrading the computer BIOS may need to be done occasionally. It may be required in order to support new types of CPUs or RAM. Upgrading the BIOS should be done whilst connected to a reliable power supply and by following the manufacturers instructions.