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I associated "Unknown" files with notepad.exe, that is to say files with no or unknown extension.

HKEY_CLASSES_ROOT\Unknown

However I am not certain of the keys I changed to that effect. I would like to restore all Keys and Values under Unknown to their "default" state, if possible.

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3 Answers

up vote 2 down vote accepted

You can pull default registry settings from Windows 7 ISO without even reinstalling Windows. First you need to create a Virtual Hard Disk to save the data you get from the ISO. My settings

Virtual hard disk size:  10 MB

the registry entry is only a few KB so the VHD can be small too. After that you will need to "Initialize Disk" and create "New Simple Volume". At this point the disk is set up. Detach the disk using "Detach VHD".

Install VirtualBox. Create a new virtual machine. Make sure to choose "Use an existing virtual hard drive file". For the new virtual machine choose

Settings > Storage

and add the ISO file. Start the virtual machine. Once its started you can export a key (Shift + F10)

reg export hkcr\unknown C:\unknown.reg

Now you can power off the virtual machine, reattach the VHD and access unknown.reg on the host computer. Example file (trimmed for brevity)

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\unknown\shell]
@="openas"
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I'm not sure what you're after, but this is a screen shot of my Unknown folder in my registry

enter image description here

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Deleting the following keys should un-associate whatever default open application you've selected for unknown type files:

HKEY_CURRENT_USER\SOFTWARE\Classes\Unknown\shell\open
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Unknown\shell\open

They may not both exist, but that's ok. Leave the other shell verbs (probably at least openas and opendlg alone).

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