Every computer is made up of a hierarchy of buses. There are local buses inside the CPU to move data around the main data path. The CPU connects to the memory and I/O devices via the system bus, and some of the I/O devices themselves connect to other buses. In fact, a network, be it a local area network (LAN) or a wide area network (WAN) is really just a bus. Fig. 16.1.1 shows a hierarchy of buses in a computer system.