A typical digital computer has many registers, and paths must be provided to transfer information from one register to another. 

•  The number of wires will be excessive if separate lines are used between each register  and all other registers in the system. 
•  A more efficient scheme for transferring information between registers in a multiple- register configuration is a common bus system. 
•  A Bus structure consists of a set of common lines, one for each bit of a register, through which binary information is transferred one at a time.

Buses are used to send control signals and data between the processor and other components.

• As the bus makes connection and transfers it is often a communications bottleneck.