The Windows XP Boot Loader

As mentioned earlier in this chapter, one of the great advantages of the approaches we're advocating in this chapter is that we're using the Windows XP boot loader. It gives you a menuing system that lets you choose which OS to start every time you boot up your computer. The following sections explain the functioning of the boot loader.

The Master Boot Record

The master boot record (MBR) is the portion of the disk that tells your computer where to find the partition boot sector. All operating systems must be started up by some type of master boot record, whether this contains the system's native code or a multiboot utility. When your system is booted, a chain of events ensues, based on your currently installed operating systems. The following is a simplified version of this chain of events for an installation containing Windows XP:

1.	After POST (power on self test), the system BIOS reads the master boot record (MBR).
2.	Control is passed to the master boot record, which then looks for the partition listed as the "active partition" in the partition table of the startup disk, as defined in your BIOS.
3.	After the active partition is found, the master boot record loads sector 0, the partition's boot sector, into memory and executes it.
4.	The partition boot sector points to NTLDR (NT loader) in the root of the partition and executes that.
5.	NTLDR reads the contents of BOOT.INI, located in the partition's root folder. BOOT.INI lists the locations and names of the computer's bootable operating systems. If more than one OS is listed, NTLDR displays a menu of OS choices. If only one is listed, which is the usual case, NTLDR fires it up directly.

At this point, the user can select the operating system to boot up. Windows 2000 and NT use this same system. In the next few sections, we'll explain how to set up multiple operating systems so that they all end up as choices in BOOT.INI.

If you are having problems with the Windows boot loader, see "Boot Menu Isn't Displayed" in the "Troubleshooting" section at the end of this chapter.

If you want to remove the Windows boot loader, see "Removing the Windows XP Boot Loader" in the "Troubleshooting" section at the end of this chapter.

The BOOT.INI Settings File

BOOT.INI handles many options for booting your system. For now, you can see your current BOOT.INI by selecting Start, Run and entering C:\boot.ini, which opens the BOOT.INI with Notepad.

The BOOT.INI file has two sections.

The [boot loader] Section

This section defines two specific settings:

• Timeout This setting defines how long the system will wait until it boots into the default operating system. This value is in seconds. A value of -1 makes the system wait indefinitely until you make a manual selection. A value of 0 makes the system boot immediately into the default operating system.

• Default This is the default operating system that will boot up, unless there is user intervention. The value of the Default entry must match the location part of one of the operating systems entries, which are described in the next section.

The [operating systems] Section

This section contains a list of operating systems installed on your computer. You can see the option for Windows XP your BOOT.INI file if you've successfully completed an installation.

Each entry in this section is of the form

 location="OS Name" /options 

where location specifies the drive and folder on which the operating system is stored, "OS Name" is a text description of the OS, and options is an optional list of operating system load modifiers. For Windows NT, 2000, XP Home Edition and Windows XP Professional, an entry might look like this:

 multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows XP Professional" 

(This strange format is a throwback from the days when Windows NT ran on the Alpha and MIPS processors. The format for Windows XP 64-bit Edition is different, and equally obtuse.) In most setups, the rdisk number indicates the physical hard drive (0 = first), and partition indicates the partition number on the drive (1 = first). The entry is followed by a folder name.

TIP

For a listing of the options permitted in boot.ini, check out http://labmice.techtarget.com/windows2000/install/bootini.htm and http://appdeploy.com/tips/bootiniswitches.shtml.

NonNT-based operating systems are loaded through files that contain images of the master boot record that the OS is usually loaded by. For example, when you install Windows XP on a system that was previously running MS-DOS, the original MS-DOS boot sector is saved in a file, and the resulting BOOT.INI entry is

 C:\="MS-DOS"