TL;DR: Pressing the power button sends power to the computer’s components, runs a hardware check, prepares the system through UEFI or BIOS, then loads the operating system so the desktop or login screen appears.
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1. Power is sent to the main parts
When the power button is pressed, the power supply sends electricity to the main components. This includes the processor (CPU), memory (RAM), and other essential parts on the motherboard.
2. The computer checks its hardware
Before starting the operating system, the computer runs a short process called POST (Power On Self-Test). It checks if the memory, processor, and other key parts are present and working. If there is a serious problem, it may show an error message or not start at all.
- This step makes sure the system does not continue with faulty or missing parts, which could cause errors later.
3. UEFI or BIOS starts
The computer then runs a small program stored on a chip called UEFI or BIOS. This program prepares the hardware for use and decides which storage device to check for the operating system.
- Without this step, the computer would not know where to look for the operating system.
3.1 Modern vs older systems
Most modern computers use UEFI, which can load faster, handle larger storage devices, and offer a more user-friendly setup compared to older BIOS systems.
4. The bootloader is loaded
The bootloader is a small program found on the storage device. Its job is to load the operating system. Some bootloaders allow you to choose from different operating systems, while others load one automatically.
- The bootloader is the link between the firmware (UEFI or BIOS) and the operating system. Without it, the OS would not start.
5. The operating system begins running
The bootloader loads the main part of the operating system, called the kernel, into memory. The kernel is responsible for controlling hardware and starting essential services.
- The kernel is the core of the operating system. Without it, the system cannot manage hardware or run programs.
6. The system loads extra features and settings
After the kernel is ready, the operating system starts additional programs and services. This includes things like network connections, display settings, and user preferences. When this process is complete, the desktop or login screen appears.
- These extra services make the computer ready for normal use and ensure your preferred settings are applied.
What can slow down startup
- Using a slow hard drive instead of a faster SSD
- Having too many programs set to start automatically
- Outdated system firmware or operating system
- Failing hardware or errors during POST
Safe shutdown reminder
Shutting down the computer properly helps keep the operating system and hardware in good condition. Avoid turning off the power directly unless the system is completely frozen and cannot be shut down normally.
Quick overview in plain steps
- Power is sent to the components.
- Hardware is checked for problems.
- UEFI or BIOS prepares the system.
- Bootloader starts the operating system.
- Kernel takes control of the hardware.
- Desktop or login screen is ready to use.
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