A data processing system for displaying data from different isolated data sources (344, 346, 348) without allowing data from a higher ranked source to reach a lower ranked source, the data processing system comprising: a display unit having a set of controls, the set of controls configured to generate control signals and the display unit is configured to simultaneously display the data from the different isolated data sources and receive user input via the controls; a plurality of data processing units (304, 306, 308) arranged in a hierarchy of rankings with at least a lower ranked data processing unit, a higher ranked data processing unit and a highest ranked data processing unit, each data processing unit in the plurality of data processing units configured to access one of the different isolated data sources (344, 346, 348), wherein the highest ranked data processing unit is linked to the display unit as to provide a single display of data from all of the data processing units to the display unit; and a plurality of data diodes (310, 312; 324, 326, 328) located in connections carrying the control signals from the set of controls of the display unit to the plurality of data processing units and located in connections from one data processing unit (304, 306, 308) to another data processing unit such that a transfer of data from an isolated data source (344, 346, 348) is allowed only from the lower ranked data processing unit to the higher ranked data processing unit of each connection until the highest ranked data processing unit is reached and is prevented from a higher ranked data processing unit to a lower ranked data processing unit in the different sources accessed by the different data processing units. a display unit having a set of controls, the set of controls configured to generate control signals and the display unit is configured to simultaneously display the data from the different isolated data sources and receive user input via the controls; a plurality of data processing units (304, 306, 308) arranged in a hierarchy of rankings with at least a lower ranked data processing unit, a higher ranked data processing unit and a highest ranked data processing unit, each data processing unit in the plurality of data processing units configured to access one of the different isolated data sources (344, 346, 348), wherein the highest ranked data processing unit is linked to the display unit as to provide a single display of data from all of the data processing units to the display unit; and a plurality of data diodes (310, 312; 324, 326, 328) located in connections carrying the control signals from the set of controls of the display unit to the plurality of data processing units and located in connections from one data processing unit (304, 306, 308) to another data processing unit such that a transfer of data from an isolated data source (344, 346, 348) is allowed only from the lower ranked data processing unit to the higher ranked data processing unit of each connection until the highest ranked data processing unit is reached and is prevented from a higher ranked data processing unit to a lower ranked data processing unit in the different sources accessed by the different data processing units.