The system bus consists of parallel (mulitple bit) connection between the system components.

Consists of three parts:

Address Bus
Data Bus
Control Bus

The width of each bus (number of wires = number of multiple bits) is fixed.

________________       Control Bus
|  ALU    | CU  |------------------
|_______________|
|PC   PS        |      Address Bus
|SP         MAR |-------------------
|IR         MDR |-------------------
|               |      Data Bus
|R0   R1    R2  |
|R3   R4    R5  |
|_______________|