Master Boot Record Takes Control
Next, the computer begins the task of loading the OS. During installation, the Windows installation program places data on the first sector of your computer's primary partition (the boot sector). That data is the Master Boot Record (MBR), and it contains executable instructions. The installation program also copies the two files that initiate the Windows boot sequence—Ntldr and Ntdetect—to the boot disk's root directory. In addition, Windows Setup copies boot.ini, the file that contains startup options, to the boot disk's root directory.
In addition to the executable instructions, the MBR has a table that defines the locations of the disk's primary partitions. (When you install Windows, you don't have to make the system partition and the boot partition the same partition, although that's the common approach.) The Windows startup files are on the system partition, and the OS files are on the boot partition. (Yes, the naming logic is backwards.)
The system partition holds the hardware-specific files that are necessary to boot Windows, including the MBR. This partition must be a primary partition, and it must be marked active. It's always drive 0, because that's the drive the BIOS accesses to turn the boot process over to the MBR. The boot partition holds the OS files (the \%systemroot% folder) and the OS support files (\%systemroot%\System).
In the last step of the hardware boot process, the computer reads the MBR into memory and transfers control of the computer to that MBR code. The executable code searches the primary partition table for a flag on a partition that indicates that the partition is bootable. When the MBR finds the first bootable partition, it reads the first sector of the partition, which is the boot sector.
Ntldr Runs
The boot-sector code reads Ntldr into memory to start the OS boot process. Ntldr contains read-only NTFS and FAT code. It starts running in real mode, and its first job is to switch the system to a form of protected mode. (For more information about these modes, see the sidebar, "Real Mode vs. Protected Mode.") This initial instance of protected mode can't perform the full physical-to-virtual translations that provide hardware protection—that feature becomes available when the OS has finished booting.
All the physical memory is now available to the OS, and the computer is operating as a 32-bit machine. Ntldr enables paging and creates the page tables. Next, Ntldr reads boot.ini from the root directory and, if you're dual booting or you've configured boot.ini to display a menu, the boot-selection menu appears on the monitor. If Ntldr is missing or corrupted, you'll see the error message Ntldr is missing. Press Ctrl-Alt-Del to restart.
Don't waste your time following the suggested sequence; you'll just recycle the system back to the same error message. You must replace Ntldr. If you created a bootable floppy for the system, you can use that disk to copy Ntldr from the floppy disk to the boot disk's root directory (usually C). If Ntldr is missing, simply copy it. If the file exists on the hard disk, it's probably corrupted. To replace it, you must first change the read-only attribute. If you don't have a bootable floppy disk, you'll have to start Setup from the Windows CD-ROM and select Repair.
Ntdetect Runs
Ntldr launches Ntdetect, which queries the system's BIOS for device and configuration information. The system sends the information that Ntdetect gathers to the registry and places it into HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION subkeys.
If a problem occurs with Ntdetect (e.g., it's missing or corrupted), you probably won't see an error message. Instead, the boot process typically just stops. The cure for a missing or corrupted Ntdetect file is to replace it. Use a bootable floppy disk to boot the computer, then copy Ntdetect from that floppy disk to the hard disk's root directory. Alternatively, start Setup from the Windows CD-ROM and select Repair.
Ntoskrnl Runs and HAL Is Loaded
After Ntdetect finishes its hardware-checking routines, it turns the OS boot process back to Ntldr, which launches ntoskrnl.exe and loads the Hardware Abstraction Layer (HAL) .dll file. (Both files are in the \%systemroot%\system32 directory.) Ntoskrnl is the core file for the Windows kernel and executive subsystems. It contains the Executive, the Kernel, the Cache Manager, the Memory Manager, the Scheduler, the Security Reference Monitor, and more. Ntoskrnl is the file that really gets Windows going. Ntoskrnl needs the hal.dll, which has the code that lets hardware interact with the OS.
You might see an error message that indicates a problem with Ntoskrnl, but the message is almost always spurious and appears because the directory referenced in boot.ini doesn't match the name of the directory into which the Windows system files were installed. This generally means that someone renamed the \%systemroot% directory or created a new directory and moved the Windows files into it. The solution is to move the files back to the location specified in boot.ini. If someone has edited boot.ini, you'll have to correct that error.
Prev. page
1
[2]
3
next page 
