The registry is a system-defined database, which is included as a part of Microsoft Windows 3.1 and later Windows operating systems. It is used by applications and other system components to store and retrieve consistent configuration data. Information regarding the registry and its use is provided in publications available from the Microsoft Developers' Network (MSDN) of Microsoft corporation, Redmond, Wash., including “Platform SDK: Performance Monitoring/Registry,” and Chapter 23 (Registry) of the “Driver Development Kit.” These publications are incorporated herein by reference. Data in the registry can be manipulated using application program interface (API) functions and services described in the above-mentioned publication, as well as with a Windows utility called the Registry Editor (Regedit.exe). Registry-related services are normally carried out by the Virtual Machine Manager (VMM) component of the Windows operating system kernel.
The registry stores data in a hierarchically-structured tree. Each node in the tree is called a key. Each key can contain both subkeys (which are themselves keys) and data entries called values. When an application is installed on a computer running Windows, it typically stores its own registry data in a branch under a key that is created for the particular application. In addition, the application may also use subkeys and values that are stored under other keys, which are shared with the operating system and/or with other applications. While the application is running, it uses the names of the appropriate keys to navigate in the registry for the purpose of reading and writing configuration data. Without the configuration data, the application is unable to run. For this reason, installation is an indispensable preparatory step to running most Windows applications that are known in the art.
During the installation procedure, the application creates any necessary new keys and writes the values that it will require in the registry. To add a new key or value to the registry, the application must first open an existing key, typically using the RegOpenKeyEx function (or a corresponding service _RegOpenKey), as described in the above-mentioned documentation. After creating a new subkey or setting a new value, the key is closed, and the new data are written to the registry. A group of keys, subkeys and values belonging to a specified branch of the registry may be saved to a backup file, known as a hive file, using the RegSaveKey function, as described in the above-mentioned MSDN documentation. Subsequently, the RegLoadKey function can be used to recall the information from the hive file and to restore it to the registry in a specified location. When the hive file contains data used by an application, it must be loaded back into the registry before the application can run.