Windows stores configuration data in registry. The registry is a hierarchical database, which you can describe it as s configuration database. Configuration database is the data which makes the operating system work. The registry is introduced to replace most text-based configuration files used in earlier versions of Windows operating systems, such as .ini files, autoexec.bat and config.sys files. The registry contains most of Windows XP’s settings for all the hardware, operating system software, non-operating system software, users, etc. Whenever a user makes changes to Control Panel settings, system policies, or installed software, the changes are reflected and stored in registry.