Bandwidth

A capacity of the medium or channel. A range within a band of frequencies or wavelengths.
The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

In computer networks, bandwidth is often used as a synonym for data transfer rate. - the amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps).

Occasionally, it's expressed as bytes per second (Bps). A modem that works at 57,600 bps has twice the bandwidth of a modem that works at 28,800 bps. In general, a link with a high bandwidth is one that may be able to carry enough information to sustain the succession of images in a video presentation.

The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a Bus with a low bandwidth. This is the main reason that new buses, such as AGP, have been developed for the PC..

In electronic communication, bandwidth is the width of the range (or band) of frequencies that an electronic signal uses on a given transmission medium. In this usage, bandwidth is expressed in terms of the difference between the highest-frequency signal component and the lowest-frequency signal component. Since the frequency of a signal is measured in hertz (the number of cycles of change per second), a given bandwidth is the difference in hertz between the highest frequency the signal uses and the lowest frequency it uses. A typical voice signal has a bandwidth of approximately three kilohertz (3 Khz); an analog television (TV) broadcast video signal has a bandwidth of six megahertz (6 MHz). Some 2,000 times as wide as the voice signal.