8SPEICHERSCHALTUNG

1457330 Data processing INTERNATIONAL BUSINESS MACHINES CORP 16 May 1974 [26 June 1973] 21688/74 Heading G4A In a data processing system having a high speed, last in-first out stack store for storing operands and operators for a processor, and a lower speed store arranged to store overflow copies of the data in the stack, roll in and roll out operations between the store and the stack store merely transfer a copy of a set of stack entries between the two stores and do not delete the entries from the source store. The arrangement reduces the number of roll operations required since, when an entry is to be made into a full stack, a roll out operation is initiated and the new entry overwrites the oldest stack entry which still remains in the stack. Then if a series of entries have to be removed from the stack, a roll-in is not necessary since the old entries still remain in the stack. Similarly following a roll-in operation, which is initiated when an entry is to be removed from the stack which is empty, entries may be entered into the stack overwriting the rolled-in entries without a roll-out operation since the entries being overwritten still remain in the lower speed store. The Specification describes in some detail the procedures involved in tracking the contents of the stack, and in addressing the lower speed store to ensure that the correct stack copies are accessed (roll-in) and the stack contents are copied into the correct locations in the lower speed store (roll-out). To this end three pointers and three status bits are used.