Smart Defrag is a free tool to defragment hard disks.
When you save files on a recently formatted hard disk, they will be stored in consecutive clusters. When you delete files, some non-adjacent clusters will become available. New files will seize the available space, filling the gaps between the files already present there. This way your files will be saved in several different areas, and your system will need more time to read them. This is called fragmentation.
Smart Defrag is able to analyze fragmentation in each of your drives, and defragment them by rearranging the files, saving them in adjacent clusters. This will result in less time spent in reading them, so your system will become faster. There are three levels of defragmentation tasks, that will generate different results. The more complex defragmentation and optimization process will produce the best results, but it will need more time to complete the task.
You can perform the defragmentation process manually, or you can tell the program to perform automatic defragmantation.