Quick Overview
- Pressing the power button sends an electrical signal to the motherboard
- BIOS/UEFI checks basic hardware through POST
- Bootloader is loaded from the storage drive
- Operating system starts and loads system files
- Desktop or login screen appears
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Ever wondered what really happens inside your computer after you press the power button? Let’s take a look at the process!
Pressing the Power Button
When you press the power button, you're not directly starting the computer—you're just sending a signal to a small chip on the motherboard that tells the power supply to wake up.
Once that happens, power flows to all the components: motherboard, CPU, RAM, graphics card, storage, and fans.
BIOS or UEFI Wakes Everything Up
Your motherboard comes with built-in software called BIOS or UEFI. This software runs before anything else and does a quick checkup to see if the important parts like memory and CPU are working.
This step is called the Power-On Self-Test (POST). If something’s wrong, the computer might beep or show an error.
Finding Something to Boot From
After POST, the BIOS/UEFI looks for a bootable device—usually your SSD or hard drive. It checks the boot order (set in BIOS settings) and hands control to a small program stored on that device called a bootloader.
Bootloader Hands It to the Operating System
The bootloader’s job is simple but important: it starts the operating system. On Windows, this is usually a file called winload.exe. On Linux, it could be something like GRUB.
This is the moment when your OS takes over the system.
Operating System Takes Over
Now the OS starts loading its files and settings. It tells the computer how to use hardware like your keyboard, screen, and storage. It also launches background services that handle tasks like security, internet access, and file management.
Your Desktop Appears
After all that, the system is ready to go. You see your desktop or login screen, and everything feels instant. But behind the scenes, it took multiple layers of checks, loads, and handoffs to get to that point.
To Sum It Up
Turning on a computer seems simple, but a lot happens in the background in just a few seconds. From powering up to checking hardware to loading your OS, it's a well-organized chain of events. Each step has a specific job, and if something fails along the way, the whole process can stop.
Knowing this helps you understand not just how your computer starts, but also why things can go wrong.
Source: Reddit
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