𝐖𝐡𝐚𝐭 𝐡𝐚𝐩𝐩𝐞𝐧𝐬 𝐰𝐡𝐞𝐧 𝐰𝐞 𝐬𝐰𝐢𝐭𝐜𝐡 𝐨𝐧 𝐚 𝐜𝐨𝐦𝐩𝐮𝐭𝐞𝐫?🤔

When the power-on button is pressed, the first chipset that gets activated is called BIOS. 𝐁𝐈𝐎𝐒 𝐬𝐭𝐚𝐧𝐝𝐬 𝐟𝐨𝐫 𝐁𝐚𝐬𝐢𝐜 𝐈𝐧𝐩𝐮𝐭 𝐎𝐮𝐭𝐩𝐮𝐭 𝐒𝐲𝐬𝐭𝐞𝐦 and is responsible for three things.

1️⃣ First, BIOS performs a Power On Self Test also known as POST. This BIOS verifies if the computer keyboard, random access memory, disk drives, and other hardware are working correctly or not. 2️⃣ Next, BIOS searches and loads the master boot record or MBR into the RAM. MBR contains a partition table that has entries regarding partitions on your storage device. 3️⃣ Now BIOS will look at the partition table and identify all the bootable partitions. If there is just one bootable partition then BIOS will proceed with the boot process else it will give you an option to select the OS that you want to boot.

📍𝐓𝐡𝐞 𝐁𝐨𝐨𝐭𝐥𝐨𝐚𝐝𝐞𝐫 👉When BIOS knows which partition to boot from, it will go to that partition and again load a program stored in the first 512 bytes of the selected partition. This program is known as a bootloader. If you are using Linux then your bootloader will either be 𝐆𝐫𝐮𝐛 𝐨𝐫 𝐋𝐈𝐋𝐎. In the case of windows, the program is very creatively called windows bootloader. 𝐓𝐡𝐞 𝐛𝐨𝐨𝐭𝐥𝐨𝐚𝐝𝐞𝐫 𝐢𝐬 𝐫𝐞𝐬𝐩𝐨𝐧𝐬𝐢𝐛𝐥𝐞 𝐟𝐨𝐫 𝐥𝐨𝐚𝐝𝐢𝐧𝐠 𝐭𝐡𝐞 𝐨𝐩𝐞𝐫𝐚𝐭𝐢𝐧𝐠 𝐬𝐲𝐬𝐭𝐞𝐦 𝐢𝐧𝐭𝐨 𝐭𝐡𝐞 𝐑𝐀𝐌.

👉Now control goes to the bootloader and the bootloader is responsible for loading the first major piece of the operating system into the RAM. 𝐓𝐡𝐢𝐬 𝐢𝐬 𝐜𝐚𝐥𝐥𝐞𝐝 𝐚 𝐤𝐞𝐫𝐧𝐞𝐥. If you are using Linux, it is called Linux kernel and on Windows, it is called WNT which stands for Windows New Technology kernel.

👉Once the kernel is loaded into the RAM, the execution control is given to it and it starts the 𝟑 𝐬𝐭𝐚𝐠𝐞 𝐩𝐫𝐨𝐜𝐞𝐬𝐬 to bring the computer to life.

1️⃣ In the first stage, the kernel performs a test known as auto-probing. 𝐀𝐮𝐭𝐨-𝐩𝐫𝐨𝐛𝐢𝐧𝐠 simply means checking if other hardware components such as wifi-card, ethernet card, hard-drives, USB devices, keyboard, mouse, touchpad, etc are working correctly or not. Once, auto-probing is done the kernel will check if the hard drive is okay or not. 2️⃣ Once all the checks are done, in the second stage, the kernel will start the system daemons. 𝐃𝐚𝐞𝐦𝐨𝐧𝐬 are programs that run in the background and provide services to other programs. There are daemons for services such as printer spooling and networking. 3️⃣ Once the daemons are running, the kernel will execute the 𝐆𝐔𝐈 𝐦𝐚𝐧𝐚𝐠𝐞𝐫 or the display manager that will actually give you a login screen.

📍On a typical modern computer, it takes about 10–15 seconds to see a login screen after pressing the power-on button. During this time, the computer actually executes over a million lines of code just to give you a login screen, which is quite magical.✨