Acoustic discs for data processing; airborne data acquisition apparatus; airwave encoded data information receivers; analogue to digital data converters; apparatus for collecting encoded data for supply to computers; apparatus for controlling the input of data; apparatus for controlling the output of data; apparatus for controlling the processing of data; apparatus for controlling the storage of data; apparatus for data collection; apparatus for data communication between laser copying machines; apparatus for data communications between computers; apparatus for data entry; apparatus for data input; apparatus for data output; apparatus for data processing; apparatus for data storage; apparatus for data transmitting; apparatus for digitising geometric data contained in documents; apparatus for guarding data communication systems against unauthorised access; apparatus for input of data; apparatus for interconnecting data processing equipment; apparatus for processing data; apparatus for processing data programmes; apparatus for processing data relating to images; apparatus for processing digital data; apparatus for programming data; apparatus for reading data; apparatus for reading data on magnetic apparatus; apparatus for reading data on optical apparatus; apparatus for reading recorded data; apparatus for receiving data; apparatus for recording data in magnetic readable form