Inside Windows Registry

The Windows Registry is perhaps the most talked about, yet least understood, component of the Windows XP operating system. The Registry is essentially a large database that stores vital system configuration data. It's all there--information about user profiles, installed applications and file types, network behaviors, even the appearance and availability of specific Windows features and interfaces.

In fact, the Registry can be an incredibly powerful and effective tweaking tool. A savvy user can drive into the Registry's deep hierarchy and find specific settings--called Keys--that can turn off the ability to install new applications or tweak Control Panel settings, for example.

By the same token, you can cause serious problems by accidentally deleting or mis-entering vital information in the Registry. So it helps to understand how the Registry works and the best ways to go about interacting with it.

The most common way to access the Registry is via the Windows Registry Editor applet (also called RegEdit). Click Start, Run and type RegEdit, then click Run. In the screen you'll see a series of folder icons, each of which is called a Key. Inside each Key may be sub-Keys, or specific data known as Values. Double-click on a Key and you'll expand it to see its sub-Keys. Or double-click a Value item to access a dialog box that lets you make changes to the data inside.

RegEdit is a capable enough application, but its value is limited to simple navigation, data entry and backup, and search operations. I personally like RegWorks (shareware, $30) as a RegEdit upgrade, especially because it packages useful Registry tweaks into an easy-to-use tool. The search capability is also worlds better than RegEdit's.

Still, for most users who access the Registry every six months or so, RegEdit is more than adequate. A quick perusal of the Registry within RegEdit shows that the database is built on five top-level Keys.

• HKEY_CLASSES_ROOT: Dedicated to storing information about file types and OLE-aware applications. OLE stands for object linking and embedding and describes how an object--such as a document--can be created in one application and embedded in another.

• HKEY_CURRENT_USER: Provides access to configuration data for the active user on the PC. The data is actually extracted from the HKEY_USERS Key--shown below--which contains user information for all accounts on the system.

• HKEY_LOCAL_MACHINE: The repository for all data about installed hardware and software.

• HKEY_USERS: Contains select preferences data for all users of the computer.

• HKEY_CURRENT_CONFIG: Extracts data from the HKEY_LOCAL_MACHINE pertaining to the active hardware configuration.

By clicking the (+) sign next to a Key, you can expand the view to reveal sub-Keys. Clicking the Key itself reveals the Values for that Key in the right-hand pane. Double-click a Value icon, and you can edit the data contained within it.

Perhaps most important, RegEdit can let you make backups--from the entire Registry to a single key. Just select the Key containing the data to back up and click File, Export. Assign the backup file a name and then navigate to the folder where you want to save it. RegEdit will save the selected Key in a file with a .reg extension. Now say you perform a change to Keys or Values under the Key you backed up and the changes disable your system. You can go back to the original Registry state just by double-clicking the .reg file you created.

Needless to say, mucking around with the Registry can be highly risky business, so it's a good idea to keep a system backup handy, in case things go spectacularly wrong.