(Or "throughput, data rate", "transmission rate") The amount of data transferred in one direction over a link divided by the time taken to transfer it, usually expressed in bits per second (bps), bytes per second (Bps) or baud. The link may be anything from an interface to a hard disk to a radio transmission from a satellite.
Where data transfer is not continuous throughout the given time interval, the data transfer rate is thus an average rate that will be lower than the peak rate. The peak or maximum possible rate may itself be lower than the capacity of the communication channel if the channel is shared, or part of the signal is not considered as data, e.g. checksum or routing information.
When applied to data rate, the multiplier prefixes "kilo-", "mega-", "giga-", etc. (and their abbreviations, "k", "M", "G", etc.) always denote powers of 1000. For example, 64 kbps is 64,000 bits per second. This contrasts with units of storage where they stand for powers of 1024, e.g. 1 KB = 1024 bytes.
The other important characteristic of a channel is its latency.
The bandwidth of a channel determines the data transfer rate but is a different characteristic, measured in Hertz. [Relationship?]