Pareto's Law is a natural law that we see everywhere in our universe. It is also known as the 80/20 rule. You've most likely heard of it expressed in different ways. e.g. 20% of the population owns 80% of the wealth. 80% of a company's profits come from 20% of its customers... and so on.
Hard drive file use is also described by Pareto's Law and that is 80% of the time, you only use 20% of your files. It's probably even more skewed than that 95% of the time, you use only 5% of all the files on your hard drive. i.e. you are accessing most of the same files over and over again.
This is the main principal behind UltimateDefrag. It applies a Pareto Analysis to your very own file system, calculates which files you use most frequently and which files you use least frequently. It then uses this information to leverage the 2 main contributors of reduced hard drive performance (see previous screen).
It segregates your files on your hard drive so that your most frequently used files are confined together on the fastest part of your hard drive and your least frequently used files are moved to the slower parts of your hard drive thereby further facilitating the former.
Let's now elaborate on those 2 main hard drive slowing principles discussed in the previous screen so you can see how it all ties in.