Classical computation

Classical computation processes information described by classical states and transition rules, in contrast with computations that use coherent quantum states. A digital classical model commonly represents data by bits; a Boolean circuit or Turing machine supplies rules for transforming those representations. A randomized algorithm adds random choices, while each particular execution still follows one sequence of classical states.

For example, an AND gate maps two input bits to one output bit, with output one only for input 11. A probabilistic selection between two inputs describes uncertainty about which classical state was used; it is not a coherent quantum superposition of those inputs. Stating the model separates the abstract information-processing rule from its physical implementation: ordinary electronic devices ultimately obey quantum physics even when their exposed computational behavior is classical.