Buses: The Processor's Mass Transit System

Just as big cities have mass transit systems that move large numbers of people, the computer has a similar system that moves millions of bits a second. Both transit systems use buses, although the one in the computer doesn't have wheels. All electrical signals travel on a common electrical bus. The term bus was derived from its wheeled cousin because passengers on both buses (people and bits) can get off at any stop. In a computer, the bus stops are the control unit, the arithmetic and logic unit, internal memory (RAM, ROM, flash, and other types of internal memory), and the device controllers (small computers) that control the operation of the peripheral devices (see Figure 2-5).
The bus is the common pathway through which the processor sends/receives data and commands to/from primary and secondary storage and all I/O peripheral devices. Bits traveling between RAM, cache memory, and the processor hop on the address bus and the data bus. Source and destination addresses are sent over the address bus to identify a particular location in memory, then the data and instructions are transferred over the data bus to or from that location.