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I need to edit a corrupted system.dat file (windows registry), I have a copy of access to this file. How do I open and edit this file using regedit?

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You should probably say that you are using Windows 95/98/ME. – Hugh Allen Nov 5 '09 at 23:40
Please clarify exactly what version of Windows this question relates to. – Kez Nov 6 '09 at 0:05
up vote 6 down vote accepted


You can open another "hive" with regedit.

  1. Start regedit.
  2. Select the HKEY_LOCAL_MACHINE root key.
  3. Go to the menu "File->Load Hive..."
  4. Choose the DAT file for the registry you wish to edit.
  5. You will be prompted for a name to load the hive into. The name does not matter. It just loads the registry hive into a subfolder using the name you provide.
  6. You can then edit the registry you just loaded in the same manner as any other registry. All changes are made in real time, just as normal.
  7. When you're done, go to the menu "File->Unload Hive..."

However, this will only work on Win2k/Xp/Vista/7, there is no way to load the registry like his in Win9x/ME.

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No good. System.dat is for windows 9x :( – Hugh Allen Nov 5 '09 at 23:39
OP didn't specify. True. – snicker Nov 5 '09 at 23:52

I wonder if a different tactic would be better? Restoring an old system.dat.

Do some operating systems keep system.old or system.something?

Booting into safe mode? Running regedit.

What I am thinking is even if you could edit it, could you repair it?

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This file belongs to a Virtual Machine, i tried boot in safe mode but the windows initialization fails. – RRUZ Nov 5 '09 at 22:37
I know exactly which registry key change to repair the file, as this was damaged by a malicious vb script. – RRUZ Nov 5 '09 at 22:42

If you have a copy can you just overwrite the bad file? Otherwise you can use your favorite binary editor. I use Hex Edit Neo. They have a freeware version also.

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