Abstract: A hierarchical data storage system comprises a main store and a smaller, faster slave store containing data currently required for processing. The memory system responds to a store access command to retrieve an item of data. In addition, for certain types of store access command, the system performs a look-ahead action to ensure that the slave store is loaded with another data item which forms part of a possible sequence. In certain cases, a test is made to determine whether the possible sequence is in the ascending or descending direction, and the look-ahead access is then made in the appropriate direction.

Abstract: A data processing system is described in which a plurality of microprogram address registers are provided, some of the registers being associated with operations involving a processor and others of the registers being associated with peripheral devices. Each register corresponds to a different level of microprogram interrupt and the registers associated with processor operations correspond to levels lower than the levels associated with the peripheral devices.