Home > Articles > Operating Systems, Server

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

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. The next few sections introduce you to the major parts of the Registry.

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.

The Keys pane, like Explorer's Folders pane, is organized in a tree-like hierarchy. The five keys that are visible when you first open the Registry Editor are special keys called handles (which is why their names all begin with HKEY). These keys are collectively referred to as the Registry's root keys. I'll tell you what to expect from each of these keys later (see the section called "Getting to Know the Registry's Root Keys" later in this chapter).

These keys all contain subkeys, which you can display by clicking the arrow to the left of each key, or by highlighting a key and pressing the plus-sign key on your keyboard's numeric keypad. To close a key, click the minus sign or highlight the key and press the minus-sign key on the numeric keypad. Again, this is just like navigating folders in Explorer.

You often have to drill down several levels to get to the key you want. For example, Figure 12.2 shows the Registry Editor after I've opened the HKEY_CURRENT_USER key, and then the Control Panel subkey, and then clicked the Mouse subkey. Notice how the status bar tells you the exact path to the current key, and that this path is structured just like a folder path.

Figure 12.2

Figure 12.2 Open the Registry's keys and subkeys to find the settings you want to work with.

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 represented 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 four-byte 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 hex 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 extension. (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.

  • See "Understanding File Types," p. 46.

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. Figure 12.3 shows this subkey for the txtfile file type.

Figure 12.3

Figure 12.3 The registered file type subkeys specify various settings associated with each file type, including its defined actions.

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 applications 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_LOCAL_MACHINE

HKEY_LOCAL_MACHINE (HKLM) contains non-user-specific configuration data for your system's hardware and applications. You'll use the following three subkeys most often:

Hardware

Contains subkeys related to serial ports and modems, as well as the floating-point processor.

Software

Contains computer-specific settings related to installed applications. The Classes subkey is aliased by HKEY_CLASSES_ROOT. The Microsoft subkey contains settings related to Windows (as well as any other Microsoft products you have installed on your computer).

System

Contains subkeys and settings related to Windows startup.

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

Understanding Hives and Registry Files

The Registry database actually consists of a number of files that contain a subset of the Registry called a hive. A hive consists of one or more Registry keys, subkeys, and settings. Each hive is supported by several files that use the extensions listed in Table 12.1.

Table 12.1. Extensions Used by Hive Supporting Files

Extension

Descriptions

None

A complete copy of the hive data.

.log1

A log of the changes made to the hive data.

.log, .log2

These files are created during the Windows 7 setup, but remain unchanged as you work with the system.

Table 12.2 shows the supporting files for each hive. (Note that not all of these files might appear on your system.)

Table 12.2. Supporting Files Used by Each Hive

Hive

Files

HKLM\BCD00000000

%SystemRoot%\System32\config\BCD-Template

%SystemRoot%\System32\config\BCD-Template.LOG

HKLM\COMPONENTS

%SystemRoot%\System32\config\COMPONENTS

%SystemRoot%\System32\config\COMPONENTS.LOG

%SystemRoot%\System32\config\COMPONENTS.LOG1

%SystemRoot%\System32\config\COMPONENTS.LOG2

HKLM\SAM

%SystemRoot%\System32\config\SAM

%SystemRoot%\System32\config\SAM.LOG

%SystemRoot%\System32\config\SAM.LOG1

%SystemRoot%\System32\config\SAM.LOG2

HKLM\SECURITY

%SystemRoot%\System32\config\SECURITY

%SystemRoot%\System32\config\SECURITY.LOG

%SystemRoot%\System32\config\SECURITY.LOG1

%SystemRoot%\System32\config\SECURITY.LOG2

HKLM\SOFTWARE

%SystemRoot%\System32\config\SOFTWARE

%SystemRoot%\System32\config\SOFTWARE.LOG

%SystemRoot%\System32\config\SOFTWARE.LOG1

%SystemRoot%\System32\config\SOFTWARE.LOG2

HKLM\SYSTEM

%SystemRoot%\System32\config\SYSTEM

%SystemRoot%\System32\config\SYSTEM.LOG

%SystemRoot%\System32\config\SYSTEM.LOG1

%SystemRoot%\System32\config\SYSTEM.LOG2

HKU\.DEFAULT

%SystemRoot%\System32\config\DEFAULT

%SystemRoot%\System32\config\DEFAULT.LOG

%SystemRoot%\System32\config\DEFAULT.LOG1

%SystemRoot%\System32\config\DEFAULT.LOG2

Also, each user has his or her own hive, which maps to HKEY_CURRENT_USER during logon. The supporting files for each user hive are stored in \Users\user, where user is the username. In each case, the ntuser.dat file contains the hive data, and the ntuser.dat.log1 file tracks the hive changes. (If a user has group policies set on her account, the user data is stored in an HKEY_USERS subkey.)

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020