We all know that when we switch on a computer system, it does take time to process “something” until a sexy girl occupies your desktop screen and GUI icons appear beside. But very few of us know what it actually does. In fact, it is one of the most crucial things that a computer should perform – The everyday process of Booting.

For a computer to undergo a successful boot, its BIOS, the operating system and hardware components must all be working at their optimum level. Even a slightest disruption in any one of these components may result in a failed boot sequence. The whole process is explained here in the simplest manner.

→ When we supply a sufficient AC to the computer system, the CPU (Central Processing Unit) initializes itself because of series of clock ticks generated by the system clock. As the ROM BIOS stores the first instruction (which is the instruction to run the power-on self test), the CPU looks for ROM BIOS for its first instruction. The power-on self test (POST) then checks BIOS chip and CMOS RAM. If there is no battery failure, it goes on initializing the CPU and checks for hardware devices like hard drives, ports, then the keyboard and mouse, ensuring at every stage they are working properly.

→ Now the BIOS waits for the CMOS chip to tell it where the OS is located. The drive order that the CMOS chip looks to in order to locate the OS is called the boot sequence. However, one can also change this sequence by altering the CMOS setup. In the appropriate boot drive, the BIOS will first come across the boot record to find the commencement of the operating system and the ensuing program file that will initialize the operating system.