Boot process of a Windows 11 computer

In short: From power-on to login a fixed chain runs: power supply and motherboard start, the UEFI firmware checks hardware (POST), loads the bootloader, which loads the Windows kernel, then drivers, services and finally the login start.

In more detail: Each stage checks and starts the next. Whoever knows the order finds startup problems much faster, because depending on the symptom a stage can be narrowed down.

In Depth

1. Power: The power supply (PSU) delivers voltage. When it has reached stable values it sends the power-good signal. Only then may the CPU start.
2. CPU initialization: The CPU resets and jumps to the fixed start address of the firmware.
3. UEFI firmware runs: It loads settings from NVRAM (CMOS data) and initializes memory, chipset and basic devices.
4. POST (power-on self-test): Self-test of CPU, RAM, graphics, keyboard. Errors show up as beeps, LEDs or error codes.
5. Secure Boot and TPM: Signatures are checked, measurements recorded in the TPM.
6. Boot device and bootloader: The firmware searches the boot order for the EFI system partition (GPT) and starts the Windows Boot Manager (bootmgfw.efi).
7. Boot manager: Reads the startup configuration (BCD), shows a menu if needed, loads winload.efi.
8. Kernel start: winload.efi loads the kernel (ntoskrnl.exe), the hardware abstraction layer, the registry hive (SYSTEM) and the boot drivers. If BitLocker is active, the drive is unlocked here with the key from the TPM.
9. Kernel initialization: Process management, memory management, further drivers, the session manager (smss.exe).
10. System services: wininit.exe, service control, security subsystem (lsass.exe), drivers for all devices.
11. Login: winlogon.exe shows the sign-in screen (password, PIN, Windows Hello). After login the user interface (explorer.exe) and autostart programs start.

• Fast startup: On shutdown Windows saves the kernel state (hibernation file) and restores it at the next start. This shortens steps 7 to 10.
• Troubleshooting: No picture and beeping → hardware/POST. “No bootable device” → boot order, partition, bootloader. Blue screen while loading → driver or kernel. Hangs at login → services, profile.

See also: POST (power-on self-test), Bootloader, Cold boot, warm boot and fast boot