Abstract: A transaction manager includes a dispatcher (22) connected to an input queue (19), one or more output queues and one or more processing module queues (11′ to 17′). The transaction manager includes input data handling means (18), responsive to transaction requests received from one or more clients, to place said transaction requests on said input queue. The transaction requests include a service code, indicative of the transaction type, and data specific to a transaction. The manager includes one or more processing modules (11 to 17), the or each processing module associated with a respective processing module queue and being adapted to process processing module queue entries and place any result of said processing on the input queue. The manager further includes output data handling means connected to the or each output queue for forwarding output queue entries to respective clients.