Definition : Defragmentation is a process that reduces the amount of fragmentation.
Fragmentation : It is the inability of a file system to lay out related data sequentially (contiguously), an inherent phenomenon in storage-backed file systems that allow in-place modification of their contents. 
Defragmentation software was the software that defrags disks.There were many defragmentation softwares available but Defraggler and Smart Defrag stands at the top.
   According to experts reviews , there was a higher competition between these too.
Defraggler : It is a piriform product.  SmartDefrag : It is iobit product.

> It defrags but slowly                          > It defrags a bit faster
> It does not optimize                           > It optimizes sytem fast and full
> It is free                                                 > It is free
There fore from the above , it is clear that smart defrag is quite better.You can also use defraggler , it has its own specialty.

Screenshots :

  • Defraggler
Defraggler at work
 
  • Smart Defrag
Smart Defrag at work