From the dawn of time, human beings have always tried to find new ways to solve problems, be more productive, work with numbers faster, and have better ways of storing information. Possibly early humans used stones to count items, which lead to the abacus, then to the slide-rule, and then later calculators. These machines allowed human beings to do these things faster and better than they could do them in their minds.
(From Wikibooks, description text under GNU Free Documentation License (GFDL))