High Performance I/O Design in the AlphaServer 4100 Symmetric Multiprocessing System

ing system based on the Alpha 21164 64-bit RISC microprocessor. This midrange system supports one to four CPUs, one to four 64-bit-wide peer bridges to the peripheral component interconnect (PCI), and one to four logical memory slots. The goals for the AlphaServer 4100 system were fast CPU performance, low memory latency, and high memory and I/O bandwidth. One measure of success in achieving these goals is the AIM benchmark multiprocessor performance results. The AlphaServer 4100 system was audited at 3,337 peak jobs per minute, with a sustained number of 3,018 user loads, and won the AIM Hot Iron price/performance award in October 1996. The subject of this paper is the contribution of the I/O subsystem to these high-performance goals. In an in-house test, I/O performance of an AlphaServer 4100 system based on a 300-megahertz (MHz) processor shows a 10 to 19 percent improvement in I/O when compared with a previous-generation midrange Alpha system based on a 350-MHz processor. Reduction in CPU utilization is particularly beneficial for applications that use small transfers, e.g., transaction processing.