DATA PROCESSING SYSTEM

PURPOSE:To realize the effective use of a common bus by providing a duplex data bus for the common bus and applying a data transfer mode setting means which sets a data transfer mode to an output device at a high speed and with high reliability. CONSTITUTION:A data processing system consists of a common bus 10, and an output device 20 and an input device 30 connected to the bus 10. The bus 10 includes the duplex data buses 11 and 12. A data transfer mode is set to the device 20 via an F-bit line 28 and an R-bit line 29 for transfer of data at a high speed and with high reliability. Thus it is possible to perform the high-speed data processing operation where two types of data are transferred via the duplex data buses 11 and 12 or the highly reliable data processing operation where the data of the same type are transferred via said duplex buses 11 and 12 and then compared with each other.