Introduction In the previous posts we have focused on the design of many combinational circuits. The outputs in those circuits were dependent on the inputs applied at that instant of taking the output. Examples of such circuits were adders like half and full adders, half and full subtractors, BCD adders, Multiplexers, decoders , etc. But what if we have to add say 5, 10 or even more numbers. Practically we only two numbers at a time, store the partial result in our memory and then add this partial result(memory content) with the next numbers to get next partial sum and so on till all the numbers have been added. To save the partial results we need  memory device. Such types of circuits