How Computer Boots up?
Have you ever given it a thought that when you press the power button on your laptop or PC, what happens behind the logo of Windows XP/Vista/Seven or Linux? From the pressing of the power button to the appearance of the login screen there are more than hundred components/peripherals that are initialized and thousand lines of code is executed during the process of booting. But what is booting? We will look inside the machine, that actually what all happens. So let us start…
Fig. 1: Image showing process of booting a computer
Fig. 2: Image showing boot sectors in Harddisk
- In the MBR the first 446 bytes are the primary boot loader, which is also referred as PBL.
- The next sixty-four bytes are the partition table, which has the record for each of the partitions.
- The MBR ends with two bytes that should be 0xAA55. These numbers act as validation that this sector is the boot sector or Master Boot Record.
- If a machine has Windows/Linux machine, then it will have only one bootloader (generally it is split into multiple stages) that is DOS/GRUB bootloader which will load the operating system.
- If a machine has 2 operating systems then the primary bootloader (GRUB if Windows and Linux are present) will give user a choice to select which operating system he/she wants that is either Windows or Linux, and corresponding to OS bootloader (secondary) DOS or GRUB will load the operating system.
Booting in Windows
Booting in Linux
Filed Under: Tutorials