Prevent Windows Disk Cleanup From Compressing Old Files

This registry hack prevents Windows Disk Cleanup Wizard from calculating the amount of space saved from compressing files on the drive. To open the registry editor, hit Windows Key and the R key at the same time. In the dialog that comes up, type in regedit and click OK.

Navigate to this registry entry.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Explorer\VolumeCaches\Compress Old Files

Double-click the (Default) key and remove the value data, click OK and close the registry editor. The value of the entry just deleted is {B50F5260-0C21-11D2-AB56-00A0C9082678} should there ever be a need to reinstate the file compression.