What Is the Registry?

The Registry is a hierarchical database that contains a variety of different types of data, including descriptions of the following:
[FONT="]
■[/FONT] The hardware installed on the computer, including the central processing unit (CPU), bus type, pointing device or mouse, and keyboard.
[FONT="]■[/FONT] Installed device drivers.
[FONT="]■[/FONT] Installed applications.
[FONT="]■[/FONT] Installed network protocols.
[FONT="]■[/FONT] Network adapter card settings.

Examples include the interrupt request (IRQ) number, memory base address, I/O port base address, I/O channel ready, and transceiver type.
The Registry structure provides a secure set of records. The data in the Registry is read,updated, or modified by many of the Windows XP Professional components.

HKEY_CLASSES_ROOT Contains software configuration data: object linking and embedding (OLE) and file-class association data. This subtree points to the Classes subkey under HKEY_LOCAL_MACHINE\SOFTWARE.

HKEY_CURRENT_USER Contains data about the current user. Retrieves a copy of each user account used to log on to the computer from the NTUSER.DAT file and stores it in the %systemroot%\Profiles\username key. This subkey points to the same data contained in HKEY_USERS\SID_currently_logged_on_user. This subtree takes precedence over HKEY_LOCAL_MACHINE for duplicated values.

HKEY_LOCAL_MACHINE Contains all configuration data for the local computer, including hardware and operating system data such as bus type, system memory, device drivers, and startup control data. Applications, device drivers, and the operating system use this data to set the computer configuration. The data in this subtree remains constant regardless of the user.

HKEY_USERS Contains the .DEFAULT subkey, which holds the system default settings (system default profile) used to display the CTRL+ALT+DELETE logon screen, and the Security Identifier (SID) of the current user.

HKEY_CURRENT_CONFIG Contains data on the active hardware profile extracted from the SOFTWARE and SYSTEM hives. This information is used to configure settings such as the device drivers to load and the display resolution to use.