Combinational logic

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This article is not about combinatory logic, a topic in mathematical logic.

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In digital circuit theory, combinational logic (also called combinatorial logic) is a type of logic circuit whose output is a function of the present input only. This is in contrast to sequential logic, in which the output depends not only on the present input but also on the history of the input.

In other words, sequential logic has memory while combinational logic does not.

Combinational logic is used in computer circuits to do boolean algebra on input signals and on stored data. Practical computer circuits normally contain a mixture of combinational and sequential logic. For example, the part of an arithmetic logic unit, or ALU, that does mathematical calculations is constructed in accord with combinational logic, although the ALU is controlled by a sequencer that is constructed in accord with sequential logic.