27. While we’re at it, is there a difference between bandwidth and throughput? I often hear these two terms used interchangeably

When applied to computer communications and networking, bandwidth represents the theoretical capacity of a communications channel expressed in bits per second. To understand the difference between bandwidth and throughput, let’s assume the network we use is a Fast Ethernet LAN. (Note: We discuss Fast Ethernet in Chapter 8.) Fast Ethernet has a maximum transfer rate of 100 Mbps. Does this mean we can expect all data transfer rates to be at 100 Mbps? No. Extraneous factors such as a node’s processing capability, input/ output processor speed, operating system overhead, communications software overhead, and amount of traffic on the network at a given time all serve to reduce the actual data rate.

Consequently, there is a difference between the maximum theoretical capacity of a communications channel and the actual data transmission rate realized. This “reality rate” is known as throughput, which refers to the amount of data transmitted between two nodes in a given period. It is a function of hardware or software speed, CPU power, overhead, and many other items. Summarizing, bandwidth is a measure of a channel’s theoretical capacity; it describes the amount of data a channel is capable of supporting. Throughput, on the other hand, informs us of what the channel really achieves. Just because a medium or LAN architecture is specified to operate at a certain data rate, it is not valid to assume that this rate will be the actual throughput achieved on any given node or group of nodes.