Is there a difference between Registry Defragging and Registry Compacting or are they basically the same process?  The names would suggest that they are different and I would guess that they both make the registry smaller.  Does RegVac Registry Cleaner perform both of these functions?  If they are different then which is the preferred or recommended process and is one process better than the other?  

   They are the same thing.  Registry Defragging is the same thing as Registry Compacting.