Abstract: A method of operating a data processing system adapted for running two or more identical-data-receiving replicated tasks in parallel, in which method messages are transferred to the replicated tasks, each message including such data and a time stamp, the messages transferred to each replicated task being sequenced in chronological order so as to be processed by the replicated task in that order, and a stability time is determined for each message, which stability time defines the instant from which the replicated task may process the message, wherein the sequencing of the messages transferred to a replicated task is based on the message time stamps plus respective first time constants, and the stability times of the messages are determined on the basis of the message stamps plus respective second time constants.