01Pressing Power Doesn't Mean Entering the System Immediately
After you press the computer's power button, you might see a brand logo after a few seconds, then a login screen or desktop appears after a while.
During this seemingly short time, the computer actually completes many tasks: Power Supply → Start Firmware → Initialize Hardware → Find Boot Device → Load Operating System → Start System Services and Interface.
Power Supply
Let hardware start working
Firmware
CPU first executes startup firmware
Initialize Hardware
Make main devices usable
Find System
Select bootable device
Enter System
Kernel, services, and interface start
02Step 1: Let Hardware Start Working Stably
The power button doesn't directly "turn on Windows." It first sends a startup request to the computer's power management circuit.
Desktop power supplies, laptop power management systems, etc., will supply stable power to needed circuits. When conditions like voltage meet requirements, the processor and other hardware enter normal startup state.
Press Power Button
Generate startup request
Power System Works
Provide appropriate power to main circuits
Processor Starts Up
Enter predetermined startup state
03Step 2: CPU First Runs Firmware
When the computer first boots, the operating system hasn't entered memory yet. So what does the CPU execute first?
The answer is the firmware on the motherboard. Modern PCs typically use UEFI; older computers often use traditional BIOS.
Firmware Storage on Motherboard
Stores UEFI / BIOS code and configuration
CPU Starts Executing
First runs startup firmware, not directly the operating system
04Step 3: Discover and Initialize Hardware
After the firmware starts running, it makes the hardware needed for startup gradually enter a usable state, such as memory, display-related hardware, storage controllers, and some peripherals.
Prepare Memory
Let later programs have a place to run and store data
Prepare Display
Let the computer display startup information or logo
Recognize Storage
Discover SSDs, hard drives, and other possible boot devices
Prepare Some Input Devices
Let startup menus and settings interfaces be operable
What Is POST?
Traditional materials often call early startup checks POST (Power-On Self-Test). Modern UEFI system initialization is more complex and doesn't necessarily show all checks to users.
The firmware doesn't "thoroughly test every hardware" before starting the system. It mainly completes the detection, configuration, and initialization needed for startup.
05Step 4: Find a Bootable System
After the hardware is ready, the firmware still needs to answer a question: Where should it boot from next?
The computer might have SSDs, external hard drives, USB drives, or even network boot options. The firmware will look for appropriate boot items according to startup configuration.
Selected Boot Item
Find the next stage startup program to run
06Step 5: Actually Start the Operating System
After the firmware finds the startup program, it hands control to the next stage. One task of the startup program is to load the core part of the operating system.
Startup Program
Runs from boot device
Load to Memory
Put needed content like operating system kernel into RAM
Start Kernel
The core part of the operating system starts running
07Step 6: From Kernel to Login Screen and Desktop
After the operating system kernel starts running, it still can't immediately say "boot is complete." It needs to continue initializing more devices and system functions.
Kernel Running
Manages resources like CPU, memory, and devices
Drivers and Devices
Let more hardware be usable by the system
System Services
Start background functions like network, login, etc.
Login and Desktop
Finally reach the familiar interface
Seeing the Desktop Is Only One of the "Last Stops" of the Startup Process
Some background services might continue starting after you see the desktop. So "desktop appears" doesn't necessarily mean all background work is completely finished.
What You've Learned
- After pressing the power button, the computer first needs to let hardware get stable power and enter startup state.
- The CPU usually first runs UEFI / BIOS firmware on the motherboard, not the operating system.
- The firmware completes hardware detection, configuration, and initialization needed for startup.
- Then the firmware finds bootable devices and startup programs according to startup configuration.
- The startup program loads necessary content like the operating system kernel into memory and hands control to the operating system.
- The operating system then initializes more devices, drivers, and services, finally displaying the login screen or desktop.
- The real startup process is more complex than the "six-step diagram," and different computers and operating systems may vary.
Next Question: After the operating system starts, why does the computer still need it running in the background? Next article: What Does the Operating System Do?