A multithreaded

processor for commercial servers This paper describes the microarchitecture of the RS64 IV, a multithreaded PowerPC ® processor, and its memory system. Because this processor is used only in IBM iSeries TM and pSeries TM commercial servers, it is optimized solely for commercial server workloads. Increasing miss rates because of trends in commercial server applications and increasing latency of cache misses because of rapidly increasing clock frequency are having a compounding effect on the portion of execution time that is wasted on cache misses. As a result, several optimizations are included in the processor design to address this problem. The most significant of these is the use of coarse-grained multithreading to enable the processor to perform useful instructions during cache misses. This provides a significant throughput increase while adding less than 5 % to the chip area and having very little impact on cycle time. When compared with other performanceimprovement techniques, multithreading yields an excellent ratio of performance gain t