What Is the BIOS?

• By Adrian Wong
• Sep 24, 2004
• Sample Chapter is provided courtesy of Prentice Hall Professional

This chapter is from the book
Breaking Through the BIOS Barrier: The Definitive BIOS Optimization Guide for PCs

The BIOS is short for Basic Input/Output System. By definition, it is the interface between software and hardware that allows software and hardware to communicate and interact with each other.

The BIOS is made up of everything that allows software and hardware to interact with each other. While you may think that the BIOS only exists in the form of the motherboard BIOS, it is actually the combination of the motherboard BIOS, the BIOS of all add-on cards in the system, as well as their device drivers.

How Does the BIOS Work?

Most people never think about what actually goes on when they do something on the computer. To most people, whenever they command the computer to do something, it just does it. No questions asked.

It isn't as simple as that. Behind the facade of the user-friendly GUI (Graphical User Interface), many things have to be done by the system for the command to be carried out.

Let's visualize the computer system as three separate layers that communicate with each other through different interfaces. The diagram to the right is of that layered division:

In our layered system, the application is the highest level. It cannot directly interact with the hardware. It can only communicate with the operating system through the API or Application Program Interface.

The API is a set of common functions that the application calls upon to get the operating system to do what it wants. Because the API is operating system-specific, it differs from operating system to operating system.

However, irrespective of the operating system, the API allows the application to get the job done without knowing how the operating system does it. The application doesn't need to know anything about the computer's hardware.

The operating system then communicates to the BIOS what it needs to carry out the application's request. The operating system never communicates directly with the hardware.

Figure 1.1 The different layers and interfaces.

The BIOS layer allows the operating system to support all manners of hardware. Each piece of hardware comes with its own BIOS and/or driver, which become part of the system's BIOS.

Therefore, the BIOS layer is dynamic and changes to match the computer's hardware configuration. It serves to mask the differences between different hardware by presenting a common interface to the operating system.

The operating system only needs to know how to communicate with the BIOS layer. It is up to the BIOS layer to translate the operating system commands into action by the hardware.

Without the BIOS layer, there's no way the operating system can access the hardware layer. The BIOS layer is the operating system's key to the hardware layer. That's how important the BIOS layer is in the computer system.