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what happens when computer start ?

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Many people who use computer just switch on the power button ,wait for some screen  and start using the computer .There is interesting process taking place in computer to start the computer .Before explaining the process here are few technical terms which comes

1.BIOS (Basic Input And Output System )

2.RAM(volatile component )

3.ROM(non volatile components )

4.Motherboard ( where all above components are placed)

The main advantage of motherboard is avoiding more cables in connecting one component to another ,otherwise it will be thousands of wire connecting all your components ,this wiring will keep on increasing when you add  more devices (components to your device ) like graphics card , printer etc. Motherboard  gives clear connectivity over the components and easy to find is there any problem with the devices

Let me start with main concept .

1.when you press the computer ,all your motherboard gets powered up and starts it own firmware .In case of any problem in this step only your computer fan will rotate you will  helpless .

2.when you multiprocessor system ,the computer will choose  one processor  in random and keep it as bootstrap processor  and run the BIOS and basic kernel initialization code

3.All the register in CPU will have some values to it and some address calculation takes place and BIOS codes starts up

4.Now BIOS starts the BIOS POST (Power On Self Test ) .This POST makes sure whether all component connected to computer is at good state suppose if the mouse is missing it will show the login screen but you can’t use the mouse when you connect after the boot but in case video card has some problem then it will show the error with the beep sound .which is normally called as blue screen of death

5.POST has also some more roles

  • verify CPU registers
  • verify the integrity of the BIOS code itself
  • verify some basic components like DMA, timer, interrupt controller
  • find, size, and verify system main memory
  • initialize BIOS
  • pass control to other specialized BIOSes (if and when required)
  • identify, organize, and select which devices are available for booting
  • discover, initialize, and catalog all system buses and devices
  • provide a user interface for system’s configuration

6.The BIOS now reads the first 512-byte sector (sector zero) of the hard disk. This is called the Master Boot Record and it normally contains two vital components: a tiny OS-specific bootstrapping program at the start of the MBR followed by a partition table for the disk.

7.Then all the basic loading takes place for the operating system  and i have give two links where you can find the detailed working




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