THE WINDOWS 7 REGISTRY

 The Registry is a central repository Windows 7 uses to store anything and everything that applies to the configuration of your system. This includes all the following:

• . Information about all the hardware installed on your
• computer
• . The resources those devices use
• . A list of the device drivers that Windows 7 loads at
• startup
• . Settings that Windows 7 uses internally
• . File type data that associates a particular type of file
• with a specific application
• . Backgrounds, color schemes, and other interface
• customization settings
• . Other customization settings for things such as the Start menu and the taskbar
• . Internet and network connections and passwords
• . Settings for Windows 7 applications such as Windows Explorer and Internet Explorer
• . Settings and customization options for many third-party applications

It’s all stored in one central location, and, thanks to a handy tool called the Registry Editor, it’s yours to play with (carefully!)


To launch the Registry Editor, select Start, type regedit into the Search box, and then press Enter. When the User Account Control dialog box shows up, enter your credentials to continue.

CAUTION

The Registry Editor is arguably the most dangerous tool in the Windows 7 arsenal. The

Registry is so crucial to the smooth functioning of Windows 7 that a single imprudent

change to a Registry entry can bring your system to its knees. Therefore, now that you

have the Registry Editor open, don’t start tweaking settings willy-nilly. Instead, read the

section titled “Keeping the Registry Safe,” later in this chapter, for some advice on pro-

tecting this precious and sensitive resource

Getting to Know the Registry

The Registry may be a dangerous tool, but you can mitigate that danger somewhat by becoming familiar with the layout of the Registry and what it various bits and parts are used for. This will help you avoid sensitive areas and stick to those Registry neighborhoods where it’s safe to poke around.

Navigating the Keys Pane

The Registry Editor is reminiscent of Windows Explorer, and it works in sort of the same way. The left side of the Registry Editor window is similar to Explorer’s Folders pane, except that rather than folders, you see keys. For lack of a better phrase, I’ll call the left pane the Keys pane.

Understanding Registry Settings

If the left side of the Registry Editor window is analogous to Explorer’s Folders pane, the right side is analogous to Explorer’s Contents pane. In this case, the right side of the Registry Editor window displays the settings contained in each key (so I’ll call it the Settings pane). The Settings pane is divided into three columns:

. Name—This column tells you the name of each setting in the currently selected key 

                (analogous to a filename in Explorer).

. Type—This column tells you the data type of the setting. There are six possible

             data types:

REG_SZ—This is a string value.

REG_MULTI_SZ—This is a series of strings.

REG_EXPAND_SZ—This is a string value that contains an environment variable name that

gets “expanded” into the value of that variable. For example, thE %SystemRoot% environment variable holds the folder in which Windows 7 was installed. So, if you see a RegistrY setting with the value %SystemRoot%\System32\, and Windows 7 is installed in C:\Windows, the setting’s expanded value is C:\Windows\System32\.

 REG_DWORD—This is a double word value: a 32-bit hexadecimal value arranged as eight

digits. For example, 11 hex is 17 decimal, so this number would be represente in DWORD form as 0x00000011 (17). (Why “double word”? A 32-bit value represents four bytes of data, and because a word in programming circles is defined as two bytes, a fouRbyte Value is a double word.)

REG_QWORD—This is a quadruple word value: a 64-bit hexadecimal value arranged as 16

digits. Note that leading zeros are suppressed for the high 8 digits. Therefore, 11 hex229 Getting to Know the Registry appears as 0x00000011 (17), and 100000000 hex appears as 0x1000000000(4294967296).

REG_BINARY—This value is a series of hexadecimal digits.

. Data—This column displays the value of each setting.

Getting to Know the Registry’s Root Keys

The root keys are your Registry starting points, so you need to become familiar with what

kinds of data each key holds. The next few sections summarize the contents of each key.

HKEY_CLASSES_ROOT

HKEY_CLASSES_ROOT—usually abbreviated as HKCR—contains data related to file extensions

and their associated programs, the objects that exist in the Windows 7 system, as well as

applications and their automation information. There are also keys related to shortcuts

and other interface features.

The top part of this key contains subkeys for various file extensions. You see .bmp for

bitmap (Paint) files, .txt for text (Notepad) files, and so on. In each of these subkeys, the

Default setting tells you the name of the registered file type associated with the exten-

sion. (I discussed file types in more detail in Chapter 3, “Customizing the File System.”)

For example, the .txt extension is associated with the txtfile file type.

These registered file types appear as subkeys later in the HKEY_CLASSES_ROOT branch, and

the Registry keeps track of various settings for each registered file type. In particular, the

shell subkey tells you the actions associated with this file type. For example, in the

shell\open\command subkey, the Default setting shows the path for the executable file

that opens.

HKEY_CLASSES_ROOT is actually a copy (or an alias, as these copied keys are called) of the

following HKEY_LOCAL_MACHINE key:

HKEY_LOCAL_MACHINE\Software\Classes

The Registry creates an alias for HKEY_CLASSES_ROOT to make these keys easier for applica-

tions to access and to improve compatibility with legacy programs.

HKEY_CURRENT_USER

HKEY_CURRENT_USER—usually abbreviated as HKCU—contains data that applies to the user

that’s currently logged on. It contains user-specific settings for Control Panel options,

network connections, applications, and more. Note that if a user has group policies set on

his account, his settings are stored in the HKEY_USERS\sid subkey (where sid is the user’s

security ID). When that user logs on, these settings are copied to HKEY_CURRENT_USER. For

all other users, HKEY_CURRENT_USER is built from the user’s profile file, ntuser.dat (located

in %UserProfile%).

Here’s a summary of the most important HKEY_CURRENT_USER subkeys:

AppEvents           Contains sound files that play when particular system events occur

                            (such as maximizing of a window)

Control Panel       Contains settings related to certain Control Panel icons

                             

Keyboard               Layout Contains the keyboard layout as selected via Control Panel’S Keyboard icon

Network                 Contains settings related to mapped network drives

Software                Contains user-specific settings related to installed applications and

                               Windows

HKEY_USERS

HKEY_USERS (HKU) contains settings that are similar to those in HKEY_CURRENT_USER.

HKEY_USERS is used to store the settings for users with group policies defined, as well as the

default settings (in the .DEFAULT subkey) which get mapped to a new user’s profile.

HKEY_CURRENT_CONFIG

HKEY_CURRENT_CONFIG (HKCC) contains settings for the current hardware profile. If your

machine uses only one hardware profile, HKEY_CURRENT_CONFIG is an alias for

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001. If your machine uses multiple hardware

profiles, HKEY_CURRENT_CONFIG is an alias for HKEY_LOCAL_MACHINE\SYSTEM\ControlSetnnn,

where nnn is the numeric identifier of the current hardware profile. This identifier is given

by the CurrentConfig setting in the following key:

HKLM\SYSTEM\CurrentControlSet\Control\IDConfigDB