See domain name registry.
The registry is a database used to store settings and options for the operating system, especially for Microsoft Windows 32-bit versions. It contains information and settings for all the hardware, software, users, and preferences of the PC. Whenever a user makes changes to "Control Panel" settings, or file associations, system policies, or installed software, the changes are reflected and stored in the registry.
(Taken from infoAnarchy.org/wiki:)
Many optimization and "hacking" tools are available to modify this portion of the Windows operating system.
On Windows 9x computers, an older installation can have a very large registry that slows down the computer's startup and can make the computer unstable.
Related
Domain name registries
Registries in the context of operating systems