The Windows XP Registry - Information courtesy PC Pro .
There are five predefined Keys in the registry Editor
Basically, the Registry is a database whose records are called 'keys' and they're structured in a hierarchical, tree-like fashion. Each sub tree holds information representing some aspect of the computer or its user: hardware and software parameters for the computer; passwords, desktop settings, software program preferences and so on for each user. Before the Registry was added in Windows 95, this sort of data was spread among the old WIN.INI and SYSTEM.INI files, plus further INI files for each application.
Each individual Registry key is like a folder containing data items called value entries (like files in a folder) and can in turn contain sub keys (like sub folders). Predefined keys exist at the top level of the tree structure and their names all begin with 'HKEY_; the H standing for 'handle', a value used to uniquely identify some resource so that it can be accessed by programs.
Here's a summary of the Windows XP Registry Root Keys and what they mean:
HKEY CLASSES ROOT
This root key stores the associations between applications and file types. It also holds the OLE details for COM objects and any file-class associations (as used in the older Windows 3.x).
HKEY_CURRENT_USER
This root key holds the profile for the user who's currently logged into the machine, including stuff like environment variables, Desktop settings, network connections, printer settings, application preferences and soon.
HKEY_LOCAL_MACHINE
This root key holds all the data about the local computer system, including low-level stuff tike its bus type, system memory, device driver details and startup control data - alt this is applicable to every user.
HKEY_USERS
This key holds all the actively loaded user profiles - including HKEY_CURRENT_USER,
which, although displayed by Regedit as a top-level root key, is a sub key of this one - as well as the default profile. This doesn't apply, however, if you're accessing a server remotely, in which case your profile will be stored in the Registry of the client machine, not on the server. When you do access the Registry on a remote system, you'll only see two keys there anyway: HKEY_USERS, and HKEY_LOCAI,_MACHINE.
HKEY_CURRENT_CONFIG
This root key holds alt the data for the current hardware profile. A hard ware profile is a set of changes to the default configurations for various services and devices. You'll find the defaults in the Software and System keys under the HKEY_LOCAL_MACHINE root key. HKEY_CURRENT_CONFIG only holds the changes to these defaults.
It isn't uncommon for these five predefined Registry keys to be mistakenly called 'Hives'. A Hive refers to a section of the Registry, and is made up of two files (one a log file) found on your hard disk in the folders %Systemroot%\System32\Config and %Systemroot%\System32\Profiles. The latter holds all the user profiles for every user of the system, while the Hive files in Config are for areas such as Default, Security and System. Hive files are only to be edited by the Registry Editor and, if you choose to so do, bear in mind that you should make backups first.
