In digital circuit theory, combinational logic is atype of digital logic which is imlplemented by Bolean Algebra, in which th output depends only on the present input.This is in contrast to sequential logic, in which the output depends not only on the present input but alos on the history of the input.
In other words, sequential logic has memory while combinational does not.
Combinational logic is used in computer circuits to perform Boolean Algebra on input signals and on sotred data. Practical Computer circuits normally contain amixture of combinatonal and sequential logic.
For example, the part of an arithmatic logic unit, or ALU, that does mathematical calculations is constructed using combinational logic.
Other circuits used in computers, such as half adders, full adders, half subtractors, full subtractors, multiplexers, demultiplexers, encoders and decoders are also made by using combinational logic