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Beginner’s Guide to Understanding CPU: Introducing the BIOS Chip

written by: Ashwin Satyanarayana•edited by: J. F. Amprimoz•updated: 6/6/2009

What happens when you switch on your computer? Why does it take so long to boot? What's happening within the computer from the time you switched on to the time the Operating System is loaded? The BIOS chip is in action. See what it is and what it does, briefly.

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    The Boot-up Process

    At the simplest level, within your computer, there are 2 levels -- A physical level which consists of the hardware, and a logical level which consists of the software. However, there is a bridge between these two levels which connects them both together for some small but yet critical functions.

    BIOS (Basic Input/Output System) is the so-called bridge that juxtaposes itself between the hardware and the software embedded within your computer. It consists of simple instructions that would have to be sent to the processor that does some mandatory checks on the system and kicks-in a sequence of programs that ultimately lead to the starting of the Operating System in use. The BIOS is stored on a ROM (read-only memory) chip directly installed on the motherboard and operates all by itself without having anything to do with your operating system.

    Here’s what the code embedded in the BIOS chip would do:

    1. Conduct the POST ( Power-on Self Test): One of the most important sequence of events that must be done before the computer starts is to take a check on the most important of the hardware parts -- like checking the processor, the Memory, disk drives, input and output devices, graphics controllers and much more. This is a crucial part of the sequence since errors would show up if something is not in place and if one of the components checked is damaged or not connected well enough. The errors are usually displayed on the screen itself or it could make themselves known through a series of beeps.
    2. The Set-up Utility: The Set-up Utility in the BIOS sets the computer hardware and optimizes it such that it is now ready to perform work. Sometimes, the numbers of settings available are more than one which is when users would have to select the best possible settings for them.
    3. The System BIOS: A lot of little things go into the proper functioning of the computer and all of these have to be controlled. As you would know by now, it is the processor that does all the controlling and the System BIOS, which literally contains all the instructions, unleashes its control over little things like the temperature monitor, the clock, peripheral devices etc. Some of this control is passed on to the operating system once it starts off.
    4. The Boot Loader: After the initial checks have been done, settings have been optimized for the computer to start, the system BIOS conducts its checks on peripherals and other hardware components, the last layer of the BIOS instructions kick-in which trigger the Operating System Software and prepares to load the OS.

Understanding the CPU

This series is all about trying to understand the inner workings of a computer -- the CPU and its intricate working mechanisms.
  1. Beginner’s Guide to Understanding the CPU: How the CPU Works
  2. Beginner’s Guide to Understanding CPU: How Parts make up the Whole
  3. Beginner’s Guide to Understanding CPU: Introducing the BIOS Chip