Chapter 6: Registry and the System Boot Process

Overview

"Complexity increases the possibility of failure; a twin-engine airplane has twice as many engine problems as a single-engine airplane."

Airplane rule

(THE JARGON FILE, VERSION 4.1.2)

If you knew what you will know when your candle was burnt low it would greatly ease your plight while your candle still burns bright

P. Hein Grooks

As I mentioned in Chapter 1, the Windows XP registry plays an extremely important role, because it actually manages the whole configuration of your system. Like in Windows NT/2000, the registry information also manages the Windows boot process. Proper understanding of the influence of the registry data on the system startup allows you to solve most startup problems, for example, when the system won't boot or starts incorrectly.

 

As I will show in this chapter, the Windows XP boot process closely resembles the Windows NT/2000 boot process. This is not surprising, because Windows XP is built on the basis of the Windows NT/2000 kernel. However, there are several improvements in this area, which will be emphasized later in this chapter. These include a logical prefetcher for faster boot, boot loader improvements, and operating system boot improvements.

You never can overestimate the role of the system registry, since it's required even in the early phases of the boot process (actually, when the operating system loader starts executing). For example, if the loader can't find the \System hive that's necessary for loading the drivers (or the hive happens to be corrupt), you'll see an error message like the one shown at the beginning of Chapter 1:

    Windows XP could not start because the following file is missing     or corrupt:    \WINNT\SYSTEM32\CONFIG\SYSTEM    You can attempt to repair this file by Starting Windows XP Setup using    the original Setup floppy disk of CD-ROM.    Select 'r' at the first screen to repair. 

When Windows XP is up and running, the System registry hive is visible under HKEY_LOCAL_MACHINE. This hive defines the loading order for all drivers installed in the system. Both the operating system loader (NTLDR) and I/O Manager access this hive.

Each driver installed in the system has its own key under HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services. Each of the driver keys, in turn, contains a start value entry. The value assigned to this entry defines the phase during the system boot process when the driver is loaded and initialized. We'll talk about the Start value in more detail later in the chapter.