scanregw.exe Scans the system registry and makes back-ups at start-up. Important should the registry become corrupt. The executable "Scanregw.exe" is located in %windir% (where %windir% is the Windows directory - C:Windows or C:Winnt) More information can be found here.

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Windows Registry Checker automatically scans the system registry for invalid entries and empty data blocks when it is started. If invalid registry entries are detected, Windows Registry Checker automatically restores a previous day's backup. This is equivalent to running the scanreg /autorun command from a command prompt. If no backups are available, Windows Registry Checker tries to make repairs to the registry. This is equivalent to running the scanreg /fix command from a command prompt. If the registry contains more than 500 KB of empty data blocks, Windows Registry Checker automatically optimizes it.