What Happens When You Start Your Computer

As was stated earlier in this chapter, the Windows XP boot sequence closely resembles that of Windows NT/2000. Listed below are the processes that take place when Windows NT/2000/XP successfully starts on an x86-based computer:

• Power On Self Test (POST)

• Initial startup process

• Boot loader process

• Selects the operating system (if you have a multi-boot system)

• Detects the hardware

• Selects a hardware profile

• Loads the kernel

• Kernel initialization process

• Logs on

Note 

The startup sequence described above applies to systems started or restarted after a normal shutdown. The startup processes begin when you do one of the following:

• Power on the computer

• Reboot the system by selecting the Shutdown option in the Enter Password window or the Restart option in the Shut Down Windows window (Fig. 6.1)

  
  Fig. 6.1: The Shut Down Windows window

However, this startup sequence does not apply when resuming from hibernate or standby modes.

Windows XP also runs on Itanium-based systems, for which the following startup stages take place:

• Power-on self test (POST) phase

• Initial startup and boot manager phase

• Kernel loading phase

• Windows XP device driver and service initialization phase

• Windows XP logon phase

When you log on, the process of loading Windows NT/2000/XP is completed, as well as are most of the initialization procedures. However, the startup can be considered successfully completed only after you log on.

The following requirements need to be met to successfully begin the Windows NT/2000/XP startup:

• Correct initialization of all the hardware.

• Presence of all the files required for starting Windows NT/2000/XP. If any of these files aren't present in the correct folder or are corrupt, the startup will fail.

Power on Self Test

When you power on or restart your computer, it undergoes the Power On Self Test (POST) procedure. The POST routine is a set of tests performed by the CPU, which, as soon as the power is applied, starts to perform the code contained in the motherboard system firmware. Firmware, known as the basic input output system (BIOS) on x86-based systems and internal adapters, contains the code necessary to start the computer.

The POST routine performs the following two tasks:

• Runs the POST diagnostic routine, which, depending on the firmware, might run some rudimentary hardware checks, such as determining the amount of memory present. The POST diagnostic routine also verifies that all hardware devices needed to start an operating system (such as a hard disk) are present and have been correctly initialized.

• After completing the diagnostic routine, POST retrieves the system configuration settings from the Complementary Metal Oxide Semiconductor (CMOS) memory, located on the motherboard. After the motherboard POST completes, each add-on adapter with built-in firmware (for example, video and hard drive controllers) runs a device-specific POST routine.

If there are problems related to the computer hardware or BIOS settings, POST will emit a series of beeps. POSTs are controlled by your computer's BIOS and may differ from machine to machine. Because of this, I recommend that you always have at hand the documentation supplied with your computer.

The topic of troubleshooting hardware problems goes beyond the range of problems discussed in this book. As a matter of fact, it deserves a separate comprehensive volume. However, I would like to recommend to you some helpful resources on the topic that would certainly help you make sense of the BIOS error codes:

• BIOS Survival Guide, available at: http://www.burks.bton.ac.uk/burks/pcinfo/hardware/bios_sg/bios_sg.htm

• Definitions and Solutions for BIOS Error Beeps and Messages/Codes, available at http://www.earthweb.com

 

The POST process for Itanium-based systems is similar to x86-based systems. The Extensible Firmware Interface (EFI) performs rudimentary hardware checks, similar to those performed by BIOS, and verifies that the devices needed to start the system are present. The EFI specification, currently implemented for Itanium-based systems only, defines a new model for the interface between operating systems and platform firmware. For more information about EFI, see the EFI link on the Web Resources page at http://www.microsoft.com/windows/reskit/webresources.