Computer booting is the process of loading and hence booting the operating system, starting from the point when users switch on the power button and ending with the appearance of Windows login screen. During this process, hundreds of components are initialized and lines of codes are performed. Well then, what is the booting sequence? Let’s see booting sequence:
On MBR disk:
Turn on the Power button → CPU pins are reset and registers are set to specific value → CPU jumps to address of BIOS (0xFFFF0) → BIOS runs POST (Power-On Self Test) and other necessary checks → BIOS jumps to MBR (Master Boot Record) → Primary Bootloader runs from MBR and jumps to Secondary Bootloader → Secondary Bootloaders loads Operating System.
Therefore, once MBR gets damaged, Windows can not boot. At this time, it is very necessary to rebuild MBR.
On GPT disk:
Booting sequence on GPT disk is the same as that on MBR disk before BIOS jumps to MBR, but after this operation there are some differences since there is no MBR on GPT disk. Under UEFI (booting from GPT disk requires UEFI motherboard, which is ruled by Microsoft), the firmware usually includes a simple boot manager which enables users to choose which OS to boot, and each OS provides its own boot loader that loads an OS kernel and transfers control to it. With the help of boot manager and boot loader the operating system can boot successfully without MBR.