Abstract: A prefetcher performs advance retrieval of data from a main memory, and places the retrieved data in an intermediate memory. The main memory is accessed by vector addressing, in which the vector access instruction includes a main memory address and a direction indicator. Main memory data is cached in an associated cache memory. The prefetcher contains a direction selector and a controller. The direction selector selects a direction of data access according to the direction indicator of a single data access transaction. The direction indicator is supplied by the processor accessing the main memory, and incorporates the processor's internal knowledge of the expected direction of future data accesses. The controller retrieves data items from the main memory, in the direction of access selected by the direction selector, and places the retrieved data items in the intermediate memory.