Keith N. Langston

IBM S/390 storage hierarchy: G5 and G6 performance considerations

The CMOS-based IBM S/390 Parallel Enterprise Servers™ have always employed the technique of memory caching to bridge the gap between processor speed and main-memory access time. However, that gap has widened with each succeeding system generation, requiring increasingly sophisticated, multiple-level cache structures in order to minimize memory-access latency. The IBM S/390® G5 and G6 include two-level caching, with a binodal second-level cache. This paper reviews the principles of cache design, discusses the performance requirements of S/390 relative to caching, and describes how those requirements are addressed by the binodal L2 cache in the G5 and G6 systems.