Q. Show the foundation of ALU design?

The foundation of ALU design starts with micro-operation implementation. Thus let's first explain how bus can be used for Data transfer micro-operations.

A digital computer has many registers and instead of connecting wires between allregisters to transfer information between them, a common bus is used. Bus is a path(comprises a group of wires) one for every bit of a register over which information istransmitted from any of different sources to any of different destinations. In general size of this data bus must be equal to number of bits in a general purposeregister.

A register is selected for transfer of data via bus with help of control signals. The common data transfer path which is the bus is made using the multiplexers. The select lines are attached to the control inputs of multiplexers and bits of one register are chosen so allowing multiplexers to select a specific source register for data transfer.