Abstract: The system interfaces with a conventional data bus 10 and address bus 12. A decoded address pulses one address line 17 and a corresponding transducer 20 launches light pulses on all sixteen fibres of a cable 21. All cables 21 lead to corresponding transducer stations from which return cables 22 with sixteen fibres return to the central station. The return cable fibres interface with transducers 23 which correspond to bits rather than transducer stations. Data from the transducer stations is therefore multiplexed on to a sixteen data bus 10. At each transducer station, the ends of the sixteen fibres 21 face the ends of the sixteen fibres 22 across a gap in which an encoding disc rotates. Clear and opaque areas around tracks on the disc provide encoding by allowing light pulses to return on selected fibres 22 in codes corresponding to angular positions of the disc. The codes are preferably Gray codes and exclusive OR gates 25 may then be employed to transcode to binary on the bus 10.