Abstract: A data communications network comprises a plurality of terminals (30, 31, . . . 34) which are interconnected by a contra-rotative ring pair of lines (35, 36), so as to be able to send data to and receive data from all the other terminals in the network. Each terminal has a pair of stations (A, B), each linked to said pair. The network is characterized in that one station associated with any one terminal is arranged to be as distant as possible in a topological sense from its associated pair.

Abstract: To ensure security of interrupt input signals to a computer system (30-3N) with minimum interruption of the running of programs in the system, two interrupt logic units (1) receive interrupt signals on leads (20-2x) from connected apparatus and store flags representing the interrupt signals in an interrupt store (2). Control logic (3) compares each input signal with presettable criteria to determine if such signal is an interrupt signal and, if so, causes the data to be transferred by way of a read register (5) to the connected computer system (30-3N). At the same time the control logic (3) of one of the units (1) designated as the active unit also causes an ouput on a lead (11) to the other unit (1) designated as the standby unit.

Abstract: A data processing system having a large number of data processors (1-4) grouped in `clusters` is used in the control of a telecommunications exchange. The arrangement is such that any one of the processors may pass data to any other of the processors, in its own cluster by way of a synchronous data bus (5), or on other clusters by way of an interface (18, 19) and an asynchronous data bus (22). The arrangement permits larger number of processors (1-4) to have access to storage without undue delay in access to stored data.