NTLDR
boot loader
NTLDR (abbreviation of NT loader) is the boot loader for all releases of Windows NT from 1993 with the release of Windows NT 3.1 up until Windows XP and Windows Server 2003. From Windows Vista onwards it is replaced by Windows Boot Manager (BOOTMGR).
NTLDR is typically run from the primary storage device, 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 a minimum, the following three (or four) files to be on the system volume:
ntldr, the main boot loader itself
NTDETECT.COM, required for booting an NT-based OS, detects basic hardware information needed for successful boot
boot.ini, which contains boot configuration
If this file was missing, then it would default to the Windows directory on the first partition of the first hard drive (which by default is WINNT on most Windows NT releases until Windows 2000, WINNT35 on Windows NT 3.5 and 3.51, or WINDOWS on Windows XP and Windows Server 2003).
Non-English versions of Windows may also load bootfont.bin.
NTLDR is launched by the volume boot record of system partition, which is typically written to the disk by the Windows FORMAT or SYS command.
History
Windows NT was designed to be compatible with Advanced RISC Computing (ARC) platforms, relying on its boot manager support and providing only osloader.exe, a loading program accepting ordinary command-line arguments specifying Windows directory partition, location or boot parameters, which is launched by an ARC-compatible boot manager when a user chooses to start a specific Windows NT operating system. However, because IBM PC compatible machines based on the x86 IA-32 platform lacked any kind of ARC support (as they predate the creation of the ARC specification), an additional layer was added specifically for that platform: a custom boot manager code presenting a text-based menu allowing the user to choose from one or more operating systems and its options configured in a boot.ini configuration file, prepended by a special StartUp module which is responsible for some preparations such as switching the CPU to protected mode.
When a user chooses an operating system from the boot menu, the following command-line arguments are then passed to the part of the osloader.exe common to all processor architectures:
load osloader=<Windows Path>\System32\NTLDRsystempartition=<Windows Partition>osloadpartition=<Windows Partition>osloadoptions=<Windows Boot Parameters>consolein=multi(0)key(0)keyboard(0)consoleout=multi(0)video(0)monitor(0)x86systempartition=<NTLDR partition>
Different versions of NTLDR were used for several different architectures.
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