INSTALL WINDOWS XP PROFESSIONAL FROM A MASTER IMAGEIN THIS EXERCISE, Y...

4. The computer loads and initializes the NTLDR file, which is the operating system

loader.

Note Windows XP Professional Setup modifies the boot sector during installation so that

NTLDR loads during system startup.

There are a number of problems that can occur during the preboot sequence, including

the following:

Improper hardware configuration or malfunctioning hardware If the BIOS

cannot detect a hard drive during its POST routine, startup fails early during the

preboot sequence and usually presents a message stating that a hard drive cannot

be located.

Corrupt MBR If your MBR becomes corrupt (a fairly common action taken by

viruses), you can generally repair it by using the Recovery Console, which is cov-

ered in Lesson 3, “Troubleshooting Problems Using Startup and Recovery Tools.”

Antivirus software can prevent and often repair a corrupt MBR.

Floppy or USB disk inserted If you see an error message stating that there is a non-

system disk or a disk error, or stating that no operating system could be found, a

common reason is that a floppy disk or a universal serial bus (USB) flash memory

disk is inserted in the drive during startup. On most computers, BIOS is configured

by default to try starting using the floppy drive or an available USB drive before it

attempts to start by using the hard drive.

What Happens During the Boot Sequence

After the computer loads NTLDR into memory, the boot sequence gathers information

about hardware and drivers in preparation for the Windows XP Professional load

phases. The boot sequence uses the following files: NTLDR, BOOT.INI, BOOT-

SECT.DOS (optional), NTDETECT.COM, and NTOSKRNL.EXE.

The boot sequence has four phases: initial boot loader phase, operating system selection,

hardware detection, and configuration selection (described in the following sections).

Initial Boot Loader Phase

During the initial boot loader phase, NTLDR switches the microprocessor from real

mode to 32-bit flat memory mode, which NTLDR requires to carry out any additional

functions. Next, NTLDR starts the appropriate minifile system drivers. The minifile sys-

tem drivers are built into NTLDR so that NTLDR can find and load Windows XP Pro-

fessional from partitions formatted with file allocation table (FAT), FAT32, or NT file

system (NTFS).

Operating System Selection

During the boot sequence, NTLDR reads the BOOT.INI file. If more than one operating

system selection is available in the BOOT.INI file, a Please Select The Operating System

To Start screen appears, listing the operating systems specified in the BOOT.INI file. If

you do not select an entry before the timer reaches zero, NTLDR loads the operating

system specified by the default parameter in the BOOT.INI file. Windows XP Profes-

sional Setup sets the default parameter to the most recent Windows XP Professional

installation. If there is only one entry in the BOOT.INI file, the Please Select The Oper-

ating System To Start screen does not appear, and the default operating system is auto-

matically loaded.

Note If the BOOT.INI file is not present, NTLDR attempts to load Windows XP Professional

from the first partition of the first disk—typically C:\.