A data processing system utilizing a descriptor ring to facilitate communication between one or more general purpose processors and one or more devices employs a system memory management unit for managing access by the devices to a main memory. The system memory management unit uses address translation data for translating memory addresses generated by the devices into addresses supplied to the main memory. Prefetching circuitry within the system memory management unit serves to detect pointers read from the descriptor ring and to prefetch address translation data into the translation lookaside buffer of the system memory management unit.