Free Registry Defrag
Full user review
"An Excellent product."
Easy interface, effective process, clean and seamless operation
It does disable the PC for a few minutes while in operation,
I like this software and have used it for years. It is so effective, it gives the numbers of of the hive being compacted (defragged) and will advise you of the % of space saved. It requires a reboot - and you're done!