How can common bus system be constructed

A common bus system could be constructed using multiplexers. These multiplexers select source register whose binary information is then placed on bus. The bus system will multiplex registers of a bit each to produce n-line common bus. The number of multiplexers required to construct bus is equal to n, where n is number of bits in each register. The size of each multiplexer must be k × 1 as it multiplexes k data lines. A bus system can be constructed through 'three-state gates' instead of multiplexers.