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MCSA/MCSE Self-Paced Training Kit (Exam 70-270): Installing ...

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4-4 Chapter 4 Modifying and Troubleshooting the Startup Process<br />

Floppy or USB disk inserted If you see an error message stating that there is a nonsystem<br />

disk or a disk error, or stating that no operating system could be found, a<br />

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

disk is inserted in the drive during startup. On most computers, BIOS is configured<br />

by default to try starting using the floppy drive or an available USB drive before it<br />

attempts to start by using the hard drive.<br />

What Happens During the Boot Sequence<br />

After the computer loads NTLDR into memory, the boot sequence gathers information<br />

about hardware and drivers in preparation for the Windows XP Professional load<br />

phases. The boot sequence uses the following files: NTLDR, BOOT.INI, BOOT-<br />

SECT.DOS (optional), NTDETECT.COM, and NTOSKRNL.EXE.<br />

The boot sequence has four phases: initial boot loader phase, operating system selection,<br />

hardware detection, and configuration selection (described in the following sections).<br />

Initial Boot Loader Phase<br />

During the initial boot loader phase, NTLDR switches the microprocessor from real<br />

mode to 32-bit flat memory mode, which NTLDR requires to carry out any additional<br />

functions. Next, NTLDR starts the appropriate minifile system drivers. The minifile system<br />

drivers are built into NTLDR so that NTLDR can find and load Windows XP Professional<br />

from partitions formatted with file allocation table (FAT), FAT32, or NT file<br />

system (NTFS).<br />

Operating System Selection<br />

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

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

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

you do not select an entry before the timer reaches zero, NTLDR loads the operating<br />

system specified by the default parameter in the BOOT.INI file. Windows XP Professional<br />

Setup sets the default parameter to the most recent Windows XP Professional<br />

installation. If there is only one entry in the BOOT.INI file, the Please Select The Operating<br />

System To Start screen does not appear, and the default operating system is automatically<br />

loaded.<br />

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

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

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