A data handling system including a plurality of groups of data originating and/or receiving devices operable asynchronously and independently with respect to each other, each group of such devices being coupled with an associated data transmission controller by means of a common data channel for buffering one unit (character) of data and providing certain basic data transmission controls for transmission of a character between an associated device and a common input/output data channel extending between the controllers and a supervisory control unit which is coupled with a main memory unit and a second data transmission channel. The second data transmission channel provides for transmission of characters between the supervisory control unit, the main memory unit and a data bank comprising a plurality of data storage or secondary data handling devices. The supervisory control unit provides the necessary elementary functional components to handle and control transmission of data between the data input/output devices and, the main memory and the data bank. The main memory unit is partitioned into a plurality of a section by means of adjustable hardware connected at each data transmission controller so as to permit only the data originating/receiving devices associated with it to communicate with an associated particular partitioned section of memory and an additional section of the memory is provided that is accessible to all partitions of the main memory unit. The supervisory control unit provides for a program stored in each particular section of the main memory unit to be executed for a predetermined period of time and then upon completion of successful branch operation in the program for a switch to performance of the program in the next section in a continuous round robbin for all sections manner. When a program instruction in one section of the main memory unit dictates performance of input/output operation a switch is made to another section but processing is suspended until the input/output operation is completed and then processing is commenced of the program instructions in the next section of the main memory unit. The supervisory control unit also includes functional components to perform certain basic arithmetic operations on the various data such as addition, subtraction, etc.