MENTAT

As established by Frank Herbert, following the defeat of the thinking machines by humanity in the Butlerian Jihad, it was forbidden to create sentient machines:

"Thou shalt not make a machine in the likeness of a human mind." — Orange Catholic Bible



The Mentat discipline was developed as a replacement for computerized calculation, just as the Bene Gesserit and the Spacing Guild took on functions previously provided by thinking machines. For thousands of years, society considered Mentats the embodiment of logic and reason.
Unlike computers, however, Mentats are not simply human calculators writ large. Instead, the exceptional cognitive abilities of memory and perception are the foundations for supra-logical hypothesizing. Mentats are able to sift large volumes of data and devise concise analyses in a process that goes far beyond logical deduction: Mentats cultivate "the naïve mind", the mind without preconception or prejudice, that can extract the essential patterns or logic of data, and deliver useful conclusions with varying degrees of certainty. They are not limited to formulating syllogisms; they are the supreme counselors of the Dune universe, filling roles as menial as archivists and clerks, or as grand as advisors to Emperors.
A Mentat's capabilities can be greatly increased by taking sapho juice, but using it leads to addiction. Sapho is extracted from the root of the Ecaz tree and its use doubles or even triples the Mentat's immense processing power. However, repeated use leaves a permanent "cranberry-colored stain" on the user's lips.