The Windows operating system registry, or simply the registry, is a database that stores configuration settings and options for the operating system and its applications. The registry is an essential component of the Windows system, as it contains information that affects the performance, security, and functionality of the system and its programs. In this article, we will explore the structure and functions of the registry, and how it can be accessed and modified by users and administrators.
Structure of the Registry
The registry is organized in a hierarchical tree format, similar to a file system. Each node in the tree is called a key, and each key can contain subkeys and values. A subkey is a container for other subkeys and values, while a value is a data entry that contains the actual information or setting. A value has a name and a data type, such as string, binary, or integer. A key can have multiple values, but only one default value, which is unnamed and displayed as (Default) in the registry editor.
The registry is divided into five main sections, called hives, which are the top-level keys in the tree. Each hive represents a different aspect of the system configuration, and has a specific name and abbreviation. The five hives are:
- HKEY_CLASSES_ROOT (HKCR): This hive contains information about file associations, COM objects, and shell extensions. It is a merged view of two other hives: HKEY_LOCAL_MACHINE\Software\Classes and HKEY_CURRENT_USER\Software\Classes.
- HKEY_CURRENT_USER (HKCU): This hive contains information about the current user's preferences, settings, and environment. It is a link to a subkey of HKEY_USERS, which contains the profiles of all users on the system.
- HKEY_LOCAL_MACHINE (HKLM): This hive contains information about the hardware, software, and system settings of the local machine. It is the most important and largest hive in the registry, and has several subkeys that store different types of data, such as system services, drivers, and security policies.
- HKEY_USERS (HKU): This hive contains information about all the user profiles on the system. Each user profile is represented by a subkey with a unique identifier, called a security identifier (SID). The subkey of the current user is linked to HKEY_CURRENT_USER, while the subkey of the default user is linked to HKEY_USERS\.DEFAULT.
- HKEY_CURRENT_CONFIG (HKCC): This hive contains information about the current hardware configuration of the system, such as display settings, device drivers, and ports. It is a link to a subkey of HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles.
In addition to these five hives, there are also some pseudo-hives, which are not stored in the registry files, but are generated dynamically by the system. These pseudo-hives include:
- HKEY_PERFORMANCE_DATA (HKPD): This hive contains performance data and counters for the system and its components, such as memory, processor, and disk usage. It is accessed by the Performance Monitor tool and other performance-related applications.
- HKEY_DYN_DATA (HKDD): This hive contains dynamic data that changes frequently, such as plug-and-play devices and network connections. It is only available on Windows 95, 98, and ME, and is obsolete on later versions of Windows.
- HKEY_CURRENT_USER_LOCAL_SETTINGS (HKCULS): This hive contains information about the current user's local settings, such as regional and language options, and desktop themes. It is only available on Windows 10 and later, and is a link to a subkey of HKEY_USERS\<SID>_Classes\Local Settings.
The registry is stored in several files, called hive files, which are located in different folders on the system drive. The location and name of these files depend on the version of Windows and the hive they belong to. For example, on Windows 10, the files for HKEY_LOCAL_MACHINE are stored in C:\Windows\System32\Config, while the files for HKEY_CURRENT_USER are stored in C:\Users\<username>\NTUSER.DAT.
Functions of the Registry
The registry serves as a central repository for the configuration data of the Windows system and its applications. The registry is used for various purposes, such as:
- Storing system settings and options, such as boot options, startup programs, service configurations, and security policies.
- Storing application settings and options, such as preferences, features, and license keys.
- Storing user settings and options, such as desktop themes, keyboard layouts, and environment variables.
- Storing hardware settings and options, such as device drivers, ports, and resources.
- Storing file associations and extensions, such as which program to use to open a certain type of file, and what actions to perform on it.
- Storing COM objects and components, such as class identifiers, interface identifiers, and type libraries.
- Storing shell extensions and handlers, such as context menu items, property sheets, and drag-and-drop operations.
The registry is accessed and modified by the system and its applications through a set of application programming interfaces (APIs), which are provided by the Windows operating system. These APIs allow the system and its applications to read, write, delete, and enumerate registry keys and values, as well as to monitor and notify changes in the registry. The registry APIs are used by various components of the system, such as the Windows kernel, the Windows shell, the Windows Installer, and the Windows Management Instrumentation (WMI).
The registry is also accessed and modified by users and administrators through a graphical user interface (GUI) tool, called the Registry Editor, which is included by default with every version of Windows. The Registry Editor allows users and administrators to view and edit the registry keys and values, as well as to import and export registry files, and to create and restore registry backups. The Registry Editor can be launched by executing regedit.exe from the Command Prompt, the Run dialog box, or the Search bar.
Conclusion
The registry is a crucial component of the Windows operating system, as it stores the configuration data of the system and its applications. The registry has a hierarchical structure, consisting of keys, subkeys, and values, which are organized into five main hives and some pseudo-hives. The registry is stored in several files, which are located in different folders on the system drive. The registry is accessed and modified by the system and its applications through a set of APIs, and by users and administrators through a GUI tool, called the Registry Editor. The registry is used for various purposes, such as storing system, application, user, hardware, file, COM, and shell settings and options. The registry is a powerful and flexible tool, but also a sensitive and complex one, and should be handled with care and caution.