Intel x86bBased system boot sequence and files

SUMMARY

There are four key files used during the boot process of Windows NT on Intel x86-based systems: BOOT.INI, NTLDR, NTDETECT.COM, and NTOSKRNL.EXE. They are responsible for starting the Boot Loader, building the hardware list, and loading the Windows NT kernel. The following describes the steps taken during the boot sequence.

Boot Sequence for x86-Based Machines

1. Power on self-test (POST).
2. Find boot device and load boot record (handled by the system BIOS). The master boot record (MBR) reads the partition table, determines the location of the boot record, and then jumps to that sector and begins execution there.
3. Windows NT bootstrap routine finds and loads NTLDR.
   
   NOTE: Steps 2 and 3 as documented on page 474 of the Windows NT System Guide are in reverse, incorrect order. The step order listed here is correct.
4. NTLDR switches processor to 32-bit flat memory mode.
5. NTLDR reads the BOOT.INI and displays operating system choices.
6. User selects an operating system (Windows NT in this example).
7. NTLDR loads NTDETECT.COM.
8. NTDETECT.COM builds the hardware list. It then passes the list and control back to NTLDR. If an operating system other than Windows NT is selected, BOOTSECT.DOS is loaded and control is passed to it.
9. NTLDR loads NTOSKRNL.EXE.
10. NTOSKRNL.EXE loads and initializes Windows NT using information from the Registry to load and initialize drivers and other system settings.