1. An apparatus comprising a computer processor for executing a plurality of predefined groups {G 1 } of tasks that process network data during consecutive time slots of equal length, wherein each task group G 1 comprises a plurality of tasks, the computer processor comprising: a task selection circuit for associating each time slot with a task group G 1 and for selecting, for each time slot, one of the tasks from the associated task group G 1 , wherein any two consecutive time slots are associated with respective different task groups G 1 ; and an instruction execution unit which is, in each time slot, to initiate execution of at most one instruction for the task selected for the time slot; wherein the instruction execution circuit includes, for each task, one or more registers storing task-specific values, such that no one of the one or more registers has to be saved or restored when a task is scheduled for execution; wherein the one or more registers include a program counter register for each task.