Registry Clean Pro

A utility to fix errors and optimize the performance of the Windows registry.

You are here: Registry Clean Pro > Online Help > File Extensions


File Extensions

HKEY_CLASSES_ROOT
HKEY_CLASSES_ROOT\Applications
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts

These keys contain references to the registered file extensions. When you install a program, it automatically creates registry entries describing the file extensions associated with it. Later, when you double-click a file having one of these extensions, the program automatically opens it. For example, when you double-click a .txt file, it is automatically opened with Notepad because the .txt file extension is associated with Notepad.

If you uninstall a program incorrectly or an error occurs during the uninstall process, the file associations registered to this program may still remain in the registry, while the program itself is removed. This causes errors when you try to open a file with an extension associated with the removed program.

To check the validity of the registered file extensions, Registry Clean Pro scans the following registry sections:

1. File Extension Records. Registry Clean Pro makes sure that every file extension record in the HKEY_CLASSES_ROOT key is associated with a valid file type record. If a file extension record is linked to a non-existing type record, the entry is removed unless it has a valid Content Type value (this value allows Internet Explorer to correctly handle files downloaded from the Internet). If a file extension record contains a pointer to a GUID, this record is considered valid and is not removed. If a file extension key contains a ShellEx subkey, this key is considered valid and is not removed.

2. File Type Records. In the HKEY_CLASSES_ROOT section, Registry Clean Pro scans all the file type records that are referenced in the file extension records. For every file type record, Registry Clean Pro checks its default icon key and shell command keys. If the file specified in the default icon key cannot be found, this key is removed from the file type record. File type keys may contain nested shell command keys (for example, Open, Print or Print To). If a shell command key refers to a file that cannot be found on all the hard drives, Registry Clean Pro removes this key from the registry. The file type key itself is never deleted.

3. Application Keys for the Open With dialog. The HKEY_CLASSES_ROOT\Applications section contains references to the applications that appear in the Open With dialog box that is shown when you try to open a file that does not have an application associated with its extension. An application key may contain a default icon key and shell command keys. Registry Clean Pro checks all these nested keys to make sure they refer to existing files. If an application key refers to a file that cannot be found on the hard drives, Registry Clean Pro removes this command from the application key. If a reference points to a file located on a network drive, Registry Clean Pro does not remove this reference. The application key itself is never deleted.

4. File Extensions for the Open With dialog. Registry Clean Pro checks all the file extensions in the HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts section. If a file extension record refers to a non-existing application key (see above), Registry Clean Pro removes this extension record from the registry.

Note: The trial version of Registry Clean Pro does not scan the File Extensions section of the registry. You should purchase the full version of Registry Clean Pro to enable this function.

Next: Shared Folders







Copyright © 2002-2008 QSX Software Group. All Rights Reserved.