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Edit MountedDevices in an Offline Windows Registry.

Registry edit icon If we have trouble with a moved or cloned Windows operating system not booting properly it can often be the result of the Windows drive letter having been changed. This topic is fully covered in this article, but If the procedures described there for accessing the MountedDevices key won't work or can't be used, then here below is how we can get to the registry of a Windows OS from outside of that install. This is often referred to as accessing an 'Offline' registry, or 'Remotely' editing a registry.

The easiest way for us to get into the registry of an OS we can't boot into is to do it from another Windows operating system. All we need to do is have the partition of the target OS visible to Windows and assigned a drive letter, then we can use Window's own regedit utility to browse to and open the registry file we want to edit. Being able to see our desired partition should be easy on a multiboot Window's machine, but we may have to assign it a drive letter in Disk Management, or maybe even unhide it if it has been set as hidden by our bootmanager. If no multiboot is available then we can remove the hard drive and connect it to another Windows machine, either by USB or a SATA connection. Another option is running Windows from bootdisk or other removable device, or even just using the Windows Recovery Environment (WinRE) from any New-Gen Windows install DVD/USB - see TechBench box below for these last options.

Open a key.
How ever we get to a place where we can run the Windows regedit utility and see and browse the partition of our troubled OS, the details of opening the MountedDevices key for editing are as detailed below. If you need some help with using regedit then you can find the basics in this outside guide, but as a novice your first foray into registry editing should clearly not be on an important machine or operating system unless you have the ability to recover from disasters by having full backups and the means to restore them.

In our example we are booted into a Windows-7 OS and we are going to open for editing the registry of a WinXP install that we can see as the F: drive. It could however be the other way around or be with Vista/8.


Regedit Mounted Devices
Start Regedit and click on HKEY_LOCAL_MACHINE to highlight it and then click File on the menu bar. A dropdown box will appear that has an option to Load Hive and selecting it will open an explorer window where we can see the F: drive we want to access which has the XP operating system on it that we want to be able to edit.


regedit select drive
Navigate into the XP folders of Windows > System32 > config and locate the file System and double click it, or highlight it and click the Open button that will be at bottom right.


regedit key name
A small text input box will open where you are expected to give a name to the new registry key you are about to create.


enter key name
It matters not what you call it, but if you start it with an A it will get top billing.


open registtry
Expand HKEY_LOCAL_MACHINE and you should see the new key, which if you also expand will reveal the MountedDevices subkey that we want to edit. Once that is highlighted the contents becomes visible and available for editing in the right hand pane. The details of changing drive letters for the purpose of recovering an unbootable operating system are explained in this article.




Unload a Registry Hive File.

When you have finished editing your new key you should unload it from the Windows registry. Be careful to follow the correct procedure for doing this as it is surprisingly easy to inadvertently just right click and delete it, which is not what you want to do.

unload reg key
Highlight the key to be removed and on the menu bar click File and this time the dropdown options will include the one to Unload Hive. Click it and you will get the following confirmation box.

confirm unload hive
Just check that you have the correct key highlighted then click Yes and you are done.

Spanner iconTech Bench More options for the more advanced amongst us.
If you have any Vista/7/8 full install DVD or USB media, or a WinRE disk, you can open regedit from the command line and use it exactly as we've described. info iconUse regedit from Win PE or RE.

Alternatively if you have a Windows Live CD/DVD such as BartPE, WindowsUBCD or Winbuilder, or you are able and motivated to build one, then you can use regedit from the desktop just as is shown above.


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