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Understanding the boot.ini File

Understanding each step in the boot process is important for troubleshooting Windows startup problems. Boot.ini is one of the first files to come into play in the boot process, therefore it's important to know how to edit, or should it become necessary, to replace the boot.ini file.

NTLDR (Ntldr) is the bootstrap loader for Windows Operating systems before Vista. The term "bootstrap" refers to "pulling oneself up by ones bootstraps", in other words starting with nothing and ending up with, in this case, the Windows Operating System loaded.

In a multiboot system, the file boot.ini, located in the root directory of the boot drive, provides a list of the available operating systems from which the user can choose. NTLDR reads boot.ini and, if more than one operating system is listed, it displays a message requesting which operating system to load.

Because boot.ini a system file, its hidden attribute is set. It will not appear in the file list unless the Folder Options are set to Show hidden files and folders.

If one of the operating systems in your multi-boot system is Linux, then GRUB or LILO may be configured as the boot loader, in that case the boot.ini file is ignored.

Windows Vista does away with NTLDR along with boot.ini and instead uses the Windows Boot Manager (Bootmgr) to read the Boot Configuration Data (BCD) database, which replaces the boot.ini file.

If you select an operating system other than Windows, NTLDR passes control to bootsect.dos. Bootsect.dos is a file that contains a copy of the boot sector found in sector 0 of the boot disk. If the Windows operating system is chosen, then the boot process moves on to the hardware detection phase.

Below is an example of a basic boot.ini file.

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINNT="Microsoft Windows 2000 Professional" /fastdetect

The timeout= setting specifies the number of seconds that the screen requesting which operating system to load will be displayed. The default= setting specifies the path - in Advanced RISC Computing (ARC) format - to the default operating system. If timeout is set to 0, NTLDR will start the default operating system immediately without displaying the operating system selection screen. If the value is set to -1, NTLDR will will display the operating system selection screen indefinitely, until the user makes a selection.

In ARC format, in multi(x), x is the number of the IDE disk controller or the SCSI adapter (always 0). In disk(z), z is the number of the IDE disk or SCSI disk (always 0). In rdisk(y), y is the number of the IDE disk (0 first, 1 second, 2 ....),(for SCSI always 0). In partition(b), b is the partition number (1,2,3,4...) with primary partitions always before extended partitions and logical disks. The last part of the path, \%SystemRoot%, is the name of the directory containing the Windows operating system.

The [operating systems] section of boot.ini defines the choices displayed on the screen In the example it specifies partition number 2 contains the Microsoft Windows 2000 Professional operating system.

There are many options you can specify in the boot.ini file. In the example, the /fastdetect option is set, which disables detection of serial mice on com ports. This option is defined by default for Windows 2000 and higher because these systems use plug-and-play device detection.

The /bootlogo option will cause Windows to display a splash screen that you define, instead of the default splash screen. Create a 16-color, 640 pixel x 480 pixel bitmap and save it in the Windows directory with the name Boot.bmp. Then add the /bootlogo option to boot.ini.

Many boot.ini options are to assist in debugging. The /bootlog option causes Windows to write a log of the boot process to the file Ntbtlog.txt. The /debug option causes the kernel debugger to load when Windows starts. The /crashdebug option causes the kernel debugger to load, but remain inactive unless a crash occurs.

Boot.ini is a text file that can be edited in Windows Notepad. You can open the boot.ini file directly in Notepad or through the System Properties dialog box. To open the System Properties dialog box, select Start | Run, then type sysdm.cpl in the text box and click on the [OK] button. In the System Properties dialog box, on the Advanced tab, under Startup and Recovery, click on the [Settings...] button. Under System Startup, click on the [Edit] button. This opens the boot.ini file in Notepad ready for editing.

In the Windows boot process, boot.ini is one of the first files to come into play, therefore it's important to know how to edit or replace the boot.ini file. There are many other options that you can specify in the boot.ini file. For more information about boot.ini options, visit: Available options for the Boot.ini file


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