A hierarchical database in which newer Microsoft Windows operating systems store their hardware and software configuration information such as user profiles, the hardware and software installed on the system, registered document types, property settings for icons, ports being used, and so on. The registry in Windows 2000, Windows NT, Windows 95, and Windows 98 replaces the INI files, such as win.ini and system.ini, that were used in the legacy Windows 3.1 and Windows for Workgroups 3.11 operating systems.
In Windows NT and Windows 2000, the registry is logically divided into five subtrees, each containing keys and subkeys (analogous to folders and subfolders) that themselves contain values (analogous to files). Physically, the registry consists of a series of hives and their transaction files located in %SystemRoot%\system32\config.
In Windows 95 and Windows 98, the logical structure of the registry is similar to that for Windows NT and Windows 2000, but the physical format is incompatible. A sixth subtree called HKEY_DYN_DATA is created dynamically and is used for performance measuring and Plug and Play configuration. The registry consists of dynamic information stored in RAM and two files in the %Win_Root% directory: system.dat, which stores computer-specific information, and user.dat, which stores user-specific information.
The main tool you should use to modify the registry is Control Panel, which provides a number of utilities for safely configuring different aspects of the system’s hardware and installed software. If you want (or need) to dig deeper into the registry, use the registry editor, but do so carefully - a single wrong value can render your operating system unbootable.