What is the Registry?

The Registry is a database used to store settings and options for the 32 bit versions of Microsoft Windows including Windows 95, 98, ME and NT/2000. It contains information and settings for all the hardware, software, users, and preferences of the PC. Whenever a user makes changes to a Control Panel settings, or File Associations, System Policies, or installed software, the changes are reflected and stored in the Registry.

The physical files that make up the registry are stored differently depending on your version of Windows; under Windows 95 & 98 it is contained in two hidden files in your Windows directory, called USER.DAT and SYSTEM.DAT, for Windows Me there is an additional CLASSES.DAT file, while under Windows NT/2000 the files are contained seperately in the %SystemRoot%\System32\Config directory. You can not edit these files directly, you must use a tool commonly known as a "Registry Editor" to make any changes (using registry editors will be discussed later in the article).

The Structure of The Registry
The Registry has a hierarchal structure, although it looks complicated the structure is similar to the directory structure on your hard disk, with Regedit being similar to Windows Explorer.

Each main branch (denoted by a folder icon in the Registry Editor, see left) is called a Hive, and Hives contains Keys. Each key can contain other keys (sometimes referred to as sub-keys), as well as Values. The values contain the actual information stored in the Registry. There are three types of values; String, Binary, and DWORD - the use of these depends upon the context.

There are six main branches, each containing a specific portion of the information stored in the Registry. They are as follows:


* HKEY_CLASSES_ROOT - This branch contains all of your file association mappings to support the drag-and-drop feature, OLE information, Windows shortcuts, and core aspects of the Windows user interface.
* HKEY_CURRENT_USER - This branch links to the section of HKEY_USERS appropriate for the user currently logged onto the PC and contains information such as logon names, desktop settings, and Start menu settings.
* HKEY_LOCAL_MACHINE - This branch contains computer specific information about the type of hardware, software, and other preferences on a given PC, this information is used for all users who log onto this computer.
* HKEY_USERS - This branch contains individual preferences for each user of the computer, each user is represented by a SID sub-key located under the main branch.
* HKEY_CURRENT_CONFIG - This branch links to the section of HKEY_LOCAL_MACHINE appropriate for the current hardware configuration.
* HKEY_DYN_DATA - This branch points to the part of HKEY_LOCAL_MACHINE, for use with the Plug-&-Play features of Windows, this section is dymanic and will change as devices are added and removed from the system.