Introducing the Registry Editor
The application you use to see what's in the Registry is the Registry Editor. It's a multithreaded application that is included with every version of Windows NT since the operating system first started shipping. To get the Registry Editor started, type regedit in the Run dialog box, which you select from the Start menu. This application, which is actually called regedit.exe, is found in the Windows subdirectory. Figure 2 shows the sequence for starting up regedit.
Figure 2 Starting regedit from the command line.
The Registry contains five standard top-level keys. Every Registry path must start with one of these root keys, just as a complete filename starts with a drive letter. Standard root keys are defined below.
HKEY_CLASSES_ROOT. File associations are defined by these keys. XP's Explorer application uses this key for information to choose icons, respond to double-clicks, and display content menus.
HKEY_CURRENT_USER. Information on the current user's profile. This is also a common location for applications to store their preferences and profiles.
HKEY_CLASSES_MACHINE. Information that applies system-wide. Windows XP stores information about hardware configurations here. Applications can also store information here that pertains to the computer rather than to users.
HKEY_USERS. Information for all users. If you configured Windows XP for multiple users, each has a subkey under this key. When the user logs on, the user's subkey becomes HKEY_CURRENT_USER.
HKEY_CURRENT_CONFIG. Defines the current configuration of the local machine. When you boot Windows XP, it determines your hardware configuration and sets this key to the appropriate subkey of HKEY_LOCAL_MACHINE/Config. This is important only if there are multiple configurations on the same machine.
By using these classes of keys with the Registry Editor, you can view, create, or modify Registry entries. Be sure you have made a backup of the Registry, however, before jumping into any of these tasks.