Generally speaking, bandwidth is directly proportional to the amount of data transmitted or received per unit time. In a qualitative sense, bandwidth is proportional to the complexity of the data for a given level of system performance. For example, it takes more bandwidth to download a photograph in one second than it takes to download a page of text in one second. Large sound files, computer programs, and animated videos require still more bandwidth for acceptable system performance. Thus, a modem that works at 57,600 bps has twice the bandwidth of a modem that works at 28,800 bps.
Frequency is measured in the number of cycles of change per second, or hertz .
Communications engineers once strove to minimize the bandwidths of all signals, while maintaining a minimum acceptable level of system performance. However, this simple rule no longer applies in general. For example, in spread spectrum communications, the bandwidths of signals are deliberately expanded. In digital cable and fiber optic systems, the demand for ever-increasing data speeds outweighs the need for bandwidth conservation. In the electromagnetic radiation spectrum , there is only so much available bandwidth to go around, but in hard-wired systems, available bandwidth can literally be constructed without limit by installing more and more cables.