Chapter 15 PC Troubleshooting 671
loading the startup files is the detection of the preferred operating system. This
information is stored in the
boot.ini
file. Windows 2000 and XP, like NT, allow for
the existence of more than one operating system. They will coexist with Windows
95, Windows 98, Windows NT, MS-DOS, and OS/2.
Note that in a BIOS-based system, the operating system provides a boot
manager to select which operating system to boot to after the POST has been
completed. Often there are compatibility issues when multiple operating
systems reside on the same computer and use a boot manager designed by one
of the operating system, such as Microsoft or Linux. The EFI has designed and
implemented a boot manager that allows the selection of the operating system to
load during the POST period. This will hopefully prevent incompatibility issues
caused by the operating system designing the boot manager rather than the EFI
standard implementing the operating system boot manager.
Once Windows 2000 or XP is selected as the operating system,
ntldr
calls
the
ntdetect.com
file. This file detects the hardware in the PC system. After the
hardware detection is complete, the boot process loads the operating system
kernel called
ntoskrnl.exe
and the hal.dll. The
hal.dll
is the hardware abstraction
layer. The Windows 2000 and XP operating systems do not allow software
programs to gain direct access to the system hardware the way that traditional
Windows programs allow. The
hal.dll
is a machine language program that serves
as the go-between for software and hardware. The
hal.dll
makes it possible for
the computer system to be hardware and device independent. It supports many
different CPU platform designs. In other words, the PC does not have to be an
IBM clone. It could use a processor such as Digital’s Alpha processor. The
ntoskrnl.exe
file is the heart of the operating system. It initializes the hardware system and
drivers. It controls and oversees the entire operating system and the processing of
instructions and files.
The entire boot process is not considered complete until you log on with the
[Ctrl] [Alt] [Delete] key combination. Once you log on, the system turns to the user
mode of operation. There are two modes of operation: user mode and kernel
mode. Kernel mode oversees the system resources and processor actions. This is
an automatic mode requiring no user intervention. User mode is the actual user
interface with the operating system. It is very restrictive in the sense that many
areas are not accessible by the user or user programs. This environment is what
makes NT-based operating system such a stable system as compared to other
earlier Microsoft Windows products. The stability is due to software and users
not being allowed to manipulate hardware resources and features.
Windows Vista Boot Sequence
In Windows Vista,
ntldr
has been replaced by the Windows Boot Manager
(bootmgr) and Windows Vista Boot Loader (winload.exe).
Ntdetect
is incorporated
into the kernel. Windows Vista also uses Boot Configuration Data (BCD) in place
of the
boot.ini
file, which is used by previous versions of Windows. This section
begins with the Boot Manager phase.
Boot Manager phase
The Boot Manager (bootmgr) is used to select which operating system to load
when more than one operating system is present on a computer. If more than one
operating system is installed on a computer, a screen similar to the one in Figure 15-28
will appear. The Windows Boot Manager screen does not appear if only one operating
kernel mode
automatic Windows
NT mode of
operation that
oversees the system
resources and
processor actions.
user mode
the actual user
interface mode
for the NT-based
operation system.
It is very restrictive
and many areas
are not accessible
by the user or user
program.