BOOTING OF AN OPERATING SYSTEM OR UNDERSTANDING OF HOW OS BOOTS

HOW OS BOOTS 

Hello every one here I am going to explain how operating system boots i.e what happens when we start our PC. This is a very large process and here I am presenting it in a short form.

When we power on the computer then it takes some time, until it gets power good signal and in this duration it sends a reset signal to CPU. Power good signal is a sign that shows that it is appropriate to start the booting sequence. The value of power good signal is generally 5V.

When the booting of BIOS starts it first do the POST (power on self test) which checks the devices that is connected and if there is an error it makes notification in the form of BEEP (A sound of indication ).

The BIOS then looks for other devices like ROM to see if any of them have BIOSes. Normally, the IDE/ATA hard disk BIOS will be found at C8000H and executed. If any other is associated have BIOS, they are executed as well.

Then the BIOS display the welcome screen. Which is nothing but the drawing which is displayed over the screen and the selected OS is chosen by reading the ASCII values of the up down arrow key.

The selected OS is then start its own MBR and the OS comes into the main memory.

Posted in: operating system