Boot Sequence

Boot sequence is the series of steps that occurs when an operating system boots on a machine.

What is Boot Sequence?

The series of steps that occurs when an operating system boots on a machine.

Alternatively, Boot Sequence can also refer to the sequence which devices a computer should check for the operating system’s boot files and the order in which those devices should be checked. The list can be changed and re-ordered in the computer’s BIOS. This is also called Boot Options or Boot Order.

Boot Sequence
Boot Sequence

Each operating system has its own particular boot sequence and uses its own specific set of boot files. Knowledge of the boot sequence for a particular operating system can aid in troubleshooting problems booting a machine on which that operating system is installed. For example, from messages displayed during the boot process, a technician can often determine whether a particular boot file is missing or corrupt.

The following table is a high-level illustration of the boot sequence for the Microsoft Windows NT operating system installed on an x86 platform. This boot sequence is divided into four phases, and different activities occur in each phase. For a successful boot of the system to occur, all four phases must be completed successfully.

The Four Phases of a Windows NT Boot Sequence

0Initial phasePower-on self test (POST); locate and load ntldr
1Boot loader phaseBlack screen: hardware detection, boot loader menu, last known good option, load ntoskrnl.exe or ntkrnlmp.exe
2Kernel phaseBlue screen: kernel initialization, create hardware hive and Clone control set, initialize devices, start services
3Logon phaseBegin Logon dialog box