NTLDR

NTLDR (abbreviation of NT Loader) is the boot loader for all releases of Microsoft's Windows NT operating system up to and including Windows XP and Windows Server 2003. NTLDR is typically run from the primary hard disk drive, but it can also run from portable storage devices such as a CD-ROM, USB flash drive, or floppy disk. NTLDR can also load a non NT-based operating system given the appropriate boot sector in a file.

NTLDR requires, at the minimum, the following two files to be on the system volume:

• NTLDR, which contains the main Boot loader itself
• boot.ini, which contains configuration options for a boot menu.

To load an NT-based OS, ntdetect.com must also be present. (Strictly speaking, only NTLDR is actually required. If boot.ini is missing, NTLDR will default to \Windows on the first partition of the first hard drive. Many desktops in the home are in this configuration and a missing boot.ini file will simply generate an error stating it is missing, then boot into Windows successfully.) In Vista, Boot information is stored in a Registry-like file called the Boot Configuration Data (BCD) store. Vista comes with a command-line tool bcdedit.com for configuring BCD. However, the command-line tool is rather complicated to use and a free editor called EasyBCD has a graphical user interface that is simpler to use.

The Volume Boot Record written to disk by the Windows NT format command attempts to load and to run the NTLDR program.

In Windows Vista and Windows Server 2008, NTLDR was replaced; the boot loader functionality is instead provided by two new components: winload.exe and the Windows Boot Manager.