A study of interleaved memory systems by trace driven simulation

Abstract

A model of interleaved memory systems for IBM System/360 and System/370 architecture has been investigated by means of a trace driven simulation. The model used is an extension of one due to G. J. Burnett and E. G. Coffman, Jr. The trace data to drive the simulation was obtained from instruction-by-instruction traces of typical IBM 360/370 programs and of the OS/VS2 operating system. The predictions of the Burnett-Coffman model are found to fit well with the simulation results for the fetching of instructions. For the fetching of operands, however, the simulation results show only about half the increase in the memory bandwidth that the Burnett-Coffman analysis predicts. This indicates that data references on the IBM 360/370 are not random in the way assumed by Burnett and Coffman. In fact, repetitive references to the same memory location occur often enough to limit the memory bandwidth increase which can be obtained by interleaving.