Boot Process in Windows and Linux with BIOS or UEFI

I still have many questions about the boot process. There are still many things confusing me, especially with UEFI. Here is what I understand and summarized:

According to Delivering fast boot times in Windows 8,the boot process begin with power on. Then the computer will do a Power-On Self-Test (POST) and load firmware configuration. It is also call a pre-boot process.

If it found a valid system disk, the boot process continue to read the master boot record (MBR). Without MBR, it cannot read the disk storage. MBR was beginning to be replaced by GUID Partition Table (GPT) in the future.

Because it may read the disk and partition, the next is to look for boot loader. For Windows XP and before, it is Windows NT Loader (NTLDR). For Vista and after, it is bootmgr.exe in EFI system partition on Unified Extensible Firmware Interface (UEFI) computers. For Linux, GRUB is in MBR while GRUB2 in a BIOS Boot partition.

NTLDR is not switchable, therefore it cannot load other operating system. But bootmgr.exe, GRUB, and GRUB2 are all switchable. They keep a list of system for boot in boot configuration data (BCD). They will follow the selection to load the operating system. that’s why when you Press F8 for Recovery Environment during Windows startup.

bootmgr.exe finds and starts the Windows loader (Winload.exe) on the Windows boot partition or Recovery Environment image in a disk partition while GRUB / GRUB2 will find your selection to start the operating system.

I will rewrite when I have more understanding the whole process. UEFI seems more complex.


  1. Wiki: Master boot record
  2. Wiki: Boot sector
  3. Microsoft: Support: Definition of System and Boot Partition
  4. Microsoft: Support: Use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows
  5. Microsoft: Windows: What are system partitions and boot partitions?
  6. TechNet Evaluation Center: Download the Evaluation: Windows 8.1 Enterprise
  7. MSDN: Delivering fast boot times in Windows 8
  8. Wiki: GUID Partition Table
  9. Wiki: EFI System partition
  10. Wiki: Unified Extensible Firmware Interface
  11. Gentoo Wiki: GRUB
  12. Gentoo Wiki: GRUB2
  13. Wiki: BIOS Boot partition
  14. Microsoft: Windows: What is Windows RE?
  15. Microsoft: Windows: Configure UEFI/GPT-Based Hard Drive Partitions
  16. 鳥哥的私房菜:第二十章、開機流程、模組管理與 Loader
  17. HP: HP Integrity Servers – EFI and EFI/POSSE Commands
  18. Windows Eight Forums: How to Turn “Fast Startup” On or Off for a Hybrid Boot in Windows 8 and 8.1

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