As per
http://support.microsoft.com/support/kb/articles/Q256/9/86.ASP
The Microsoft Computer Dictionary, Fifth Edition, defines the registry as:
A central hierarchical database used in Microsoft Windows 9x, Windows CE, Windows NT, and Windows 2000 used to store information necessary to configure the system for one or more users, applications and hardware devices.
The Registry contains information that Windows continually references during operation, such as profiles for each user, the applications installed on the computer and the types of documents that each can create, property sheet settings for folders and application icons, what hardware exists on the system, and which ports are being used.
The Registry replaces most of the text-based .ini files used in Windows 3.x and MS-DOS configuration files, such as the Autoexec.bat and Config.sys. Although the Registry is common to several Windows platforms, there are some differences among them.
Registry data is stored in binary files.