Expository writing explains something about a limited topic. it is
formal
informal

Read the excerpt from the code book. without much hope of a theoretical breakthrough, cryptanalysts have been forced to look for a technological innovation. if there is no obvious way to reduce the number of steps required for factoring, then cryptanalysts need a technology that will perform these steps more quickly. silicon chips will continue to get faster as the years pass, doubling in speed roughly every eighteen months, but this is not enough to make a real impact on the speed of factoring—cryptanalysts require a technology that is billions of times faster than current computers. consequently, cryptanalysts are looking toward a radically new form of computer, the quantum computer. if scientists could build a quantum computer, it would be able to perform calculations with such enormous speed that it would make a modern supercomputer look like a broken abacus. the author’s purpose in this paragraph is to convince the readers to pursue a career in analysis. explain the need for faster technology in cryptanalysis. entertain with interesting stories about supercomputers. argue for more money to develop a quantum computer.