Abstract: Data processing equipment suitable for recording details of manually connected telephone calls has a plurality of operator stations with keyboards and VDU's connected in groups to operator's control units which respond to keyed instructions to obtain data from peripheral units storing such data and for recording on magnetic tape cartridge the details of the calls. Each operator's control unit is connected to eight operator stations but is capable of handling inputs from twelve such stations. In the event of breakdown of an operator's control units the eight stations allocated to it are divided into two groups of four which are transferred to the two control units adjacent to that which has broken down. Among the criteria used to determine whether a control unit has broken down are the filling of buffer stores and the failure to perform a particular operation within a predetermined interval of time following the previous performance of that operation.