Ntldr

NTLDR (abbreviation for NT Loader) is the boot loader for Windows NT, including its later versions (2000/XP/Longhorn). NTLDR can be run either from a floppy disk or the primary hard disk. The partition on which it is executed must be FAT or NTFS. Windows 2000 (NT 5.0) and above support FAT32, while older versions only support FAT12 or FAT16. 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 two files to be on the active partition: NTLDR, which contains the main boot loader itself, and boot.ini, which contains configuration options for a boot menu. To load an NT-based OS, ntdetect.com must also be present.

Startup Process

When booting, NTLDR does the following in order:

1. Places the processor in 32-bit flat memory mode
2. Accesses the appropriate file system (FAT or NTFS)
3. Reads boot.ini and prompts the user with the boot menu accordingly
4. If a non NT-based OS is selected, then the file bootsect.dos is loaded and given control
5. If a NT-based OS is selected, then ntdetect.com is started, gathering information about the computer's hardware
6. The information returned by ntdetect.com is passed to the kernel, ntoskrnl.exe, which is then started. ( et al, 2000)

Example boot menu

The following is an example NTLDR boot menu:

Please select the operating system to start:
                                                                                

      Microsoft Windows XP Professional
      Microsoft Windows 98

Use ↑ and ↓ to move the highlight to your choice.
Press Enter to choose.
Seconds until highlighted choice will be started automatically: 30













For troubleshooting and startup options for Windows, press F8.

Boot.ini

NTLDR allows the user to choose which operating system to boot from at the menu; for NT and NT-based operating systems, it also allows the user to pass preconfigured options to the kernel. The menu options are stored in boot.ini, which itself is located in the root of the same disk as NTLDR.

For NT-based OSs, the location of the operating system is written as an Advanced RISC Computing (ARC) path.

Example

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
C:\="Microsoft Windows 98"

If the boot loader timeout option in boot.ini is set to 0, the NTLDR boot menu does not appear.

NT Kernel switches

• /3gb
• /basevideo
• /baudrate=nnn
• /bootlog
• /burnmemory
• /crashdebug
• /debug
• /debugport=comx
• /fastdetect
• /maxmem=nn
• /nodebug
• /noguiboot
• /nopae
• /noserialmice:comx
• /numproc
• /onecpu
• /pae
• /pcilock
• /safeboot
• /safeboot:dsrepair
• /safeboot:minimal
• /safeboot:minimal(alternateshell)
• /safeboot:network
• /sos
• /w95
• /w95dos
• /year

References

• Microsoft. (2000). Windows 2000 professional resource kit. 1st ed. Redmond, WA: Microsoft Press. ISBN 1-57231-808-2.