Wednesday, October 14, 2009

The Bootup Sequence of Windows XP Consist of 5 Major Steps

1) Pre-boot. This phase is started when the computer is first power on. The computer runs a power-on-self-test, which it will be probing for Plug and Play Hardware devices. After this process, the Basic Input/Output System (BIOS) will locates the Master Boot Record (MBR), which it uses to locate and start the Operating System.

2) Boot. In this phase the NTLDR is used to initialize the system and change the microprocessor from real mode to 32-bit flat memory mode. Next the following files are used to locate and load the Operating System


3) Kernel Load. During this phase the NTLDR loads the Ntoskrnl.exe file, but does not initialize it. It also loads the HAL and HKEY_LOCAL_MACHINE Registry key during this phase. This registry key is used to load the device drivers and some of the low level services, which are critical for a successful logon. The information that is created at this phase is called the control set. After this only the NTLDR initializes and passes over the control to the Ntoskrnl.exe (NT Kernel).

4) Kernel Initialization. Upto this point the screen was in text mode. From here onwards the screen changes and the Windows logo appear. During this phase 4 tasks are accomplished.

(a) The Hardware key is created using the data found on the file.

(b) The clone control set is created, which is a copy of the control set which was created at the kernel load phase.

(c) The kernel initializes the low-level device drivers that were loaded in the kernel load phase and loads and initializes the higher-level device drivers that are dependent upon the low-level device drivers.

(d) Finally the Session Manger loads all of the Higher-Level Services, including the Win32 sub-system, which is controls the graphical user interface, video display and all I/O devices. Also the WinLogon process is started.

5) Logon. In this stage the winlogon.exe starts the Local Security Authority (LSA), which provide a logon screen.

After a successful logon the System copies the Clone Control Set to the Last Known Good Configuration (LKG) Control Set. This will not be changed until the next successful logon.


  1. What is the fix for the "NTLDR is missing" error?

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  3. NTLDR is the boot loader for XP and many other Windows Operating Systems.

    The best and easiest way to fix this issue is to follow these steps.

    1. Boot the computer using a Windows XP CD
    2. When you get the prompt to "Hit ENTER to install" and "R to Repair", Select R'
    3. If an Administrator Password has been set you will be prompted for it. Else you will enter a command prompt.
    4. Type the following to re-write the NTLDR : "fixmbr"[ENTER]
    5. "fixboot" will re-write the entire boot sector.
    6. Restart the computer and it will be back in business.

    Note- The above is for a Windows XP Computer. Windows VISTA and Windows 7 the process is much more robust.