Applications are able to interact directly with the Registry to add, change, or remove this data, and the Registry in turn saves altered application data to the permanent hive files from which it is built, retrieving it when the applications are launched.

In this way, the Registry is continuously bombarded with changes made by applications, users, and even Windows itself. As new applications are installed and old applications are removed, and as registered applications continue accessing and changing Registry data, they often leave small bits of themselves behind in the form of orphaned Registry entries. Taken individually or over a short time, they're just more stuff your Registry has to go through when it loads. But if they are allowed to accumulate, the combined clutter of all these small errors can become debilitating as the Registry increases in both size and disorganization, causing Windows to frequently stall or crash and eventually preventing it from booting up altogether.

For this reason, periodic Windows Registry cleaning will not only optimize your system's performance, but can also extend its life expectancy by keeping the Registry's growth uniform and in check.

Software solutions for Windows Registry cleaning

There are many third-party Windows Registry cleaning utilities available that can make this necessary cleaning completely painless. These cleaner utilities will scan your Registry for invalid references to items that have been moved or made obsolete.

The whole scanning process will generally include the following:

Scanning Registry files

Before performing the Registry scan, cleaning utilities will scan all your hard drives to build a list of its files and folders. It will later compare items on this list with Registry entries that refer to a file without specifying its full path in order to prevent their incorrect deletion.

Scanning Startup

If you move or delete executable files that Windows automatically runs upon Startup, the Registry entries referring to the file remain but are invalid and can cause delays and error messages when you boot up your computer. The cleaning utility will scan all entries in the Startup section, and remove any whose files cannot be found.

Scanning Shared DLLs (Dynamic Link Libraries)

DLLs contain stored functions that can be called on to perform various tasks. Since they can be shared by multiple applications, they are stored in the SharedDLL key of the registry. If a shared DLL is deleted or moved, these registry entries become invalid and applications can't them. If the cleaning utility can't find a DLL that is listed in the ShardDLLs key, the registry entry pointing to the DLL will be removed.

Scanning File Extensions

If programs are incorrectly or incompletely uninstalled on your computer, the file extension associations may still remain in the Registry as orphans. The cleaning utility will scan File Extension Records and File Type Records in the Registry to check the validity of registered file extensions. It will remove each File Extension record that is not associated with a valid File Type. All File Extension records that contain pointers to a GUID (Globally-unique Identifier) are considered valid, as they are used to uniquely identify OLE/COM classes.

Creating Backups

Almost all repair and cleaner utilities allow you to easily create and store backups of your registry before scanning or making any changes to your Registry. Whether the Windows Registry cleaning utility you choose does or not, it is very important to create a backup before performing scans or making changes to your Registry.