Oct 9, 2010


 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.

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—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:
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—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
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 (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:

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