Description of the Registry Files in Windows Millennium Edition (266270)

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Logically, the registry is one data store. Physically, the registry consists of three different files for maximum network-configuration flexibility. Although Microsoft Windows 95 and Microsoft Windows 98 use the User.dat, System.dat, and sometimes the Policy.pol files, Windows Me separates the HKEY_CLASSES_ROOT hive to its own file and uses the registry to store information in the Classes.dat and System.dat files.

The following sections describe the Classes.dat, User.dat, and System.dat files.

The Classes.dat File

This file contains software settings, essential information about OLE, and association mappings to support the drag-and-drop feature, Windows shortcuts (which are OLE links), and core aspects of the Windows user interface.

The User.dat File

The User.dat file contains user-specific information, or user profiles. This file contains information such as logon names, desktop settings, and Start menu settings. During Windows Setup, the User.dat file is automatically stored as a hidden file in the Windows folder, but the file does not necessarily remain in the Windows folder. If you enable user profiles, users settings are stored in the Windows\Profiles folder. In a network setting, this file may be located on a central server.

The System.dat File

The System.dat file contains hardware-specific or computer-specific settings (the hardware profile). This file contains all of the hardware configuration, Plug and Play settings, and program settings. The System.dat file is always stored as a hidden file on the local computer in the Windows 98 folder.