In a computer or on a network, a bus is a transmission path on which signals are dropped off or picked up at every device attached to the line. Only devices addressed by the signals pay attention to them; the others discard the signals. According to Winn L. Rosch, the term derives from its similarity to autobuses that stop at every town or block to drop off or take on riders
In general, the term is used in two somewhat different contexts:
(1) A bus is a network topology or circuit arrangement in which all devices are attached to a line directly and all signals pass through each of the devices. Each device has a unique identity and can recognize those signals intended for it.
(2) In a computer, a bus is the data path on the computer’s motherboard that interconnects the microprocessor with attachments to the motherboard in expansion slots (such as hard disk drives, CD-ROM drives, and graphics adapters).