Bus - general concepts.

Data path represents a set of circuits interconnected by an internal bus.

Externally, bus needed to connect the cpu with other electronic curcuits.
  Memory
  I/O
    Keyboard, video.
    Harddrives, other 2ndary storage.

Next Four general catagories Power - supplies power to circuits and other devices. Address - selects circuits to interact with cpu. Memory or I/O interfaces. Data - path to transfer data between cpu or other master device and other "slave" circuit or device. Control - provides Timing Synchronization (busy, waiting, ready) Data control (data direction)