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Learning the BIOS Boot up process

by: Vianca C. Villar | 04 Feb, 2010 04:10:32

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Ever wonder what goes on in the background or within the computer's system or motherboard once you press the power button on? Which program runs or software runs first?  Let this article take you through the process.

Once your computer is turned on, its microprocessor found on a single micro chip which functions as its central processing unit (CPU) awaits for its first command. The instruction cannot come from the Operating system since it is stored on a hard disk and the microprocessor would need to be directed to it. This is where the function of the Basic Input/output System or BIOS, pronounced as "bye-ose" comes into play. It is a system soft ware that ensures all programs, chips, hard drives, ports and even hardware are working properly as it powers up your computer and let you start working.

It simply allows the microprocessor to communicate with the Operating System and its applications and then detects all hardware (mouse, keyboard) installed or attached to get your computer all ready to start.

Here are the steps that BIOS follows to fire up your computer:

  1. confirm your CMOS set up for your computer's settings
  2. Initiate interrupt handlers/device drivers
  3. Enable  system registers and power operation
  4. Conducts power-on self-test (POST)
  5. Presents the system's settings
  6. Decides on which devices are bootable
  7. Begins bootstrap sequence

BIOS primarily checks information kept on a tiny 64 byte (RAM) chip found on a complementary metal oxide semiconductor (CMOS). It displays pertinent information particular to your system's default settings which can be modified by the user or as deemed necessary by BIOS.

A typical PC will show you a CMOS set-up dependent on their BIOS manufacturer with several options such as:  System Time/Date; Boot Sequence; Plug and Play; Mouse/Keyboard; Drive Configuration; Memory; Security; Power Management and Exit.   Hitting a key or combinations like "Esc," "Del," "F1," "F2," "Ctrl-Esc" or "Ctrl-Alt-Esc" will allow you to go into the CMOS set-up screen. Although, you can alter your computer's custom settings take extra precaution in doing so to avoid any system issue that may arise.

Acting as an interpreter between the operating system and its components or hardware are the Interrupt handlers. To cite an example, this type of software enables the CPU to know which key you pressed on the keyboard via signals and passes it to the Operating System. While, device drivers detect components attached to your computer such as   keyboard, hard drive, floppy drive and mouse.

BIOS may also perform a power-on self-test (POST) to confirm that all hard ware or components are functioning. It will then eventually try to launch the Operating System as determined by the boot sequence - the order in which BIOS will begin loading the Operating System.

It's amazing to note that a simple process such as turning on your computer requires a series of steps to make it work. It'll start from the microprocessor receiving its first command to initiating the sequence of booting the operating system to powering all computer hardware or components which are made possible by this one essential software known as, BIOS.

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