The size of the registry key exported with Reg.exe is very large

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We have already seen how we can use the integrated command line utility Reg.exe to perform almost any task you can do with regedit.exe. You can also use Reg.exe to save a registry key to a hive file.

However, if you determine that the Reg.exe utility does not compress a registry key when the utility stores a registry key in a hive file, you can apply the patch published by Microsoft.

If you try to make copies of registry keys using the reg save command when you export the registry key to a hive file, you will notice that the registry key does not compress the key during the export process. This makes the exported key size very large. In such a scenario, you can apply this Microsoft patch.

This patch fixes the problem that can occur on a system running Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows Server 2008, Windows 8 or Windows Server 2012.

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After downloading and installing this patch 973817, use the switch /c in the reg save command to compress the registry key.

For example, this command compresses the HVAC system subkey :

reg store hklmsystem %windir%system32configsystem.lkg /y /c

I hope this will help you solve your problem.

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