Abstract: A data transmission system to enable data to be transmitted along a transmission path at a rate C greater than the upper data rate limit A of the path. A data transmitter driven by an internal clock at C Hertz transmits data along the transmission path and at the same time also transmits a derived clock signal at a frequency C/N Hertz where (C/N)<A along the path. At the receiver the data is clocked into a series of data stores under the control of the transmitted clock signal and is thereafter recombined into a serial stream under the control of the clock signal driving the receiver.