NTLDR

NTLDR, short for NT Loader, is the boot loader used by certain Windows NT-based operating systems, notably Windows 2000, Windows XP, and Windows Server 2003. It runs after the computer’s BIOS hands control to the boot sector on the active partition and is responsible for loading the Windows kernel and core system components into memory.

During the boot process on BIOS-based machines, the system’s boot sector loads NTLDR. NTLDR then loads NTDETECT.COM to identify hardware and reads boot.ini to determine available operating systems and the default selection. Based on the user’s choice or the default setting, NTLDR loads the kernel NTOSKRNL.EXE, the hardware abstraction layer HAL.DLL, and other essential components, initializes core subsystems, and transfers control to the kernel. The kernel then starts the session manager and presents the logon interface.

Key files associated with the loader include NTLDR itself, NTDETECT.COM, boot.ini, NTOSKRNL.EXE, and HAL.DLL. Boot.ini is a text file that lists installed operating systems and boot options; NTLDR uses it to present boot choices to the user.

NTLDR is part of the Windows NT boot sequence and is commonly associated with the “NTLDR is missing” error, which can indicate that NTLDR, NTDETECT.COM, or boot.ini are absent or corrupted on the boot partition. Recovery typically involves restoring these files from installation media or a recovery console, fixing the boot sector, and repairing boot.ini.

Legacy and successors: NTLDR was used by Windows 2000, XP, and Server 2003. Beginning with Windows Vista, the boot process shifted to BOOTMGR and the Windows Boot Manager, along with the winload.exe loader, marking a shift away from NTLDR in modern Windows releases.