Synapse tightly coupled multiprocessors: a new approach to solve old problems

TLDR: Using a non-write-through cache and the Synapse Expansion Bus, Synapse has designed a symmetric, tightly coupled multiprocessor system, capable of being expanded on line and under power from two through twenty-eight processors with a linear improvement in system performance.

Abstract: The theoretical merits of a tightly coupled multiple-processor/shared-memory architecture have long been recognized. Two major problems in designing such an architecture are the performance limitations imposed by shared-memory bus contention in cached processors and multiple-processor data coherency. In the Synapse system, memory contention was significantly reduced by designing a processor cache employing a non-write-through algorithm, which minimized bandwidth between cache and shared memory. The multicache coherency problem was solved by a new bussing scheme, the Synapse Expansion Bus, which includes an ownership level protocol between processor caches. Using a non-write-through cache and the Synapse Expansion Bus, Synapse has designed a symmetric, tightly coupled multiprocessor system, capable of being expanded on line and under power from two through twenty-eight processors with a linear improvement in system performance.