The stack processing method is used to com- pare the cost-performance (/access)betweenthefollowing:1)two−levelandthree−levelhierarchies;and2)hierarchiesusingrandomaccessandserialaccessmemoriesasabackingstore.Itwasfoundthatbusswidthbetweenlevelsinthehierarchystronglyaffectsthesystemcost−performance,andtheaccesstimeratiobetweenthebackingstoreandbuffersomewhatless.Withthetechnologycostassumptionsusedinthisstudy,thethree−levelhierarchydoesnothaveasgoodafigureofmerit(/access) as the two-level hierarchy unless the access time ratio exceeds about fifty. Also, random access devices are advantageous over serial access devices for backing store applications only when the memory capacity is less than 1 Mbyte. For capacities of 4 Mbyte and 16 Mbyte serial access stores with shift register lengths of 256 bit and 1024 bit, respectively, look favorable. Copyright © 1973 by The Institute of Electrical and Electronics Engineers, Inc.