sed to provide communica- tions capability to different departments within an organization. Note that each departmental switch uses a Fast Ethernet connection from the switch to a departmental server. Also note that one port on each depart- mental server uses a gigabit connection to an enterprise switch. That switch, which is shown at the top of the tiered switching hierarchy in Original Ethernet Slot Time Figure 5.13 Half-duplex Gigabit Start Frame Destination Source bytes Preamble Length/ Ethernet uses a carrier Delimiter Check Extension Address Address 46-1500 extension scheme to Sequence extend timing SO that the slot time consists 512-byte Slot Time of at least 512 bytes. Team-Fly® Fiber in the LAN Figure 5.14, represents a true Gigabit Ethernet switch with all ports on the switch operating at 1 Gbit/s. Note that enterprise servers are connected this switch, which enables employees at different locations within the organization to rapidly access enterprise servers. Also note that because numerous servers are clustered together at one location, this networking strategy results in a group of servers connected to a common switch, which is referred to as "establishing a server farm." Limitations No discussion of Gigabit Ethernet would be complete without mention- ing two of its key limitations. Those limitations are the bus speed and the disk transfer capacity of many servers, which cannot keep pace with the transmission rate of the technology and the lack of redundancy. BUS SPEED AND DISK TRANSFER To appreciate the importance of bus speed, consider Table 5.5, which lists the throughput in megabytes Figure 5.14 Using a Gigabit switch in a tiered net- work environment. Gigabit (Enterprise) Switch Gigabit connections Departmental Switch Departmental Legend: workstations departmental server enterprise server Chapter Five TABLE 5.5 Width, bits Throughput, Mbytes/s Theoretical Bus Throughputs PCI, 33 MHz PCI, 33 MHz PCI, 66 MHz PCI, 66 MHz per second for seven types of PC buses. In examining the entries in Table 5.5,