Resource control allocation

In a system where a single resource in the form of a data bus BS is shared among a plurality of users in the form of Modules M, control of the bus is restricted to not more than one module M at a time. Each module is assigned a different n-digit binary identity number, all the identity numbers containing the same number m of ones, and associated with BS there are n lines AB which perform the wired-OR function. When a request for the control of BS is made, the module or modules making that request apply their identity numbers to AB, and a decoder in each module, or one common to all modules, determines whether the resulting number carried by AB contains exactly m, or more than m, ones. If it contains more than m ones, indicating two or more requestors, arbitration between them takes place in a known manner to determine which of them shall control BS first. But if the number on AB contains exactly m ones there can be only one requestor and so arbitration is dispensed-with, allowing the requestor to obtain control with less delay. In an alternative form of the invention, an additional set of bus lines allows the arbitration means to be used concurrently with the determination of the OR-function of the requestors' identity numbers, and if this shows that only one requestor is present, the arbitration process is abandoned.