Windows XP Boot Components

Windows XP Boot Components

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The boot procedure in Windows XP

This document describes the essential components required in booting up a PC running Windows XP, from power on to loading NTLDR, and the technique and events involved in presenting the boot menu listing available OS entries and booting into the selected item.

Boot Procedure (Generic)

Before we go into the details of how Windows XP’s boot process works, it’s vital first to grasp the fundamental concepts that underpin any bootloader, beginning with how the computer gets turned on. You can find a more extensive explanation of the normal BIOS boot-up routine here, but for now, the following will suffice:

As can be seen, a chain of handoffs begins when you turn on your computer, beginning with the BIOS and continuing through the MBR, boot sector, and finally, the bootloader.

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There are two possible explanations for this jumbled chain. The first is for portability: because all interactions are abstracted to a set of agreed-upon behaviors, you can take out and replace any one of the components powering/facilitating these four steps without having to replace the others. This is especially important because each layer is traditionally manufactured, written, designed, or developed by a different entity.

The second is a more technical limitation: in the early stages, the amount of space available for executable bootloader code is severely limited, but as you progress up the ladder,,, it rises. The MBR, for example, is only 512 bytes (really 446 bytes if the partition table is removed!) — by contrast, this paragraph is twice as long! The boot sector is similarly limited in size (though the exact limits depend on the filesystem of the current partition). You can only write extensive boot code after you reach the last step of the actual bootloader file.

This lengthy procedure is in charge of everything up until the Windows XP bootloader, NTLDR (short for NT loader), is ultimately discovered and invoked by the code in the NTFS or FAT32 boot partition’s boot sector.

Boot Components for Windows XP

Once the active partition’s boot-related code has been run, it will look in its root directory for a file called NTLDR (the partition itself is expected to be of NTFS or FAT32 format). While NTLDR has received fame and glory in the past, it does not do all on its own and is just a third of the solution at best.


The bootloader used by Microsoft Windows, beginning with Windows NT and continuing through Windows 2000, Windows XP, and Windows Server 2003, is known as NTLDR. NTLDR is no longer in use, having been replaced by BOOTMGR, the new Windows bootloader, with the release of Windows Vista. It’s usually found in the active partition’s root directory on the first boot drive. This is normally C: and the same partition that Windows is installed on in most Windows XP installs, although this is not always the case. NTLDR uses this capability extensively, especially when more than one OS is installed on the same computer (on distinct partitions).


Boot.ini is a plain-text file on the active partition of the first boot drive’s active partition. NTLDR reads the boot.ini file for boot configuration information and utilizes it to display and boot various operating systems. BOOT.INI1 can contain references to Windows NT-based operating systems (Windows NT, Windows 2000, Windows XP, and Windows Server 2003), as well as entries pointing to “chain loaders” (bootloaders for non-Windows OSes saved to a file) to load non-Windows OSes. This is where new operating systems are added to the bootloader and where existing entries’ boot options/parameters can be adjusted or removed.

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The file is part of Windows NT-based operating systems and is used to detect hardware components required to start the operating system during boot up. The NTLDR starts during the startup process, and collects hardware information to send to the ntoskrnl.exe program (Windows kernel). All NT-based operating systems, including Windows XP, 2003, and Vista, have NTDETECT.COM. It collects the following types of hardware data:

  • video adapters
  • hardware date and time
  • keyboards
  • hard drives
  • mouse
  • and others (bus and adapter types, floppy disks etc.)

NTLDR passes the information and configuration collected and generated by NTDETECT to the Windows NT kernel (ntoskrnl.exe). While the Windows kernel has other ways of identifying and connecting with your PC’s underlying hardware (via the HAL or hardware abstraction layer), NTDETECT information is critical for easing first access to drives and other devices.

The Boot Sequence for Windows XP

As previously stated, NTLDR loads a Windows installation from a local drive using BOOT.INI and NTDETECT.COM. The boot procedure is summarized in the diagram below, which highlights the interactions between the major components of the Windows XP boot system:


I hope you found this information helpful. Please fill out the form below if you have any queries or comments.

User Questions

1. What is the location of the boot folder in Windows XP?

It’s usually found in the active partition’s root directory on the first boot drive. This is normally C: and the same partition that Windows is installed on in most Windows XP installs, although this is not always the case.

2. What components of the computer are involved in the boot process?

A computer’s BIOS, operating system, and hardware components must all be operational to boot successfully; failure of any of these three pieces will almost always result in a failed boot sequence.

3. What are your options for starting the boot process?

When you press the power button, power is sent to the bootloader in the cache memory, starting the boot process. The bootloader program runs a POST or Power On Self Test, and if everything checks out, the Basic Input Output System, or BIOS, is enabled, and the operating system is found and loaded.

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4. Windows XP Boot Issue: techsupport – Reddit

Windows XP Boot Issue from techsupport

5. Cannot boot into USB 2.0 to install Windows XP – Reddit

Cannot boot into USB 2.0 to install Windows XP from techsupport