Tradeoffs between coupling small and large processors for transaction processing

A methodology is developed to determine the number of processors needed to satisfy transaction throughput and response time requirements for processors of different MIPS (sizes). The minimum MIPS per processor required to satisfy response time and throughput constraints in a transaction processing complex of N coupled systems is also determined. For realistic overhead assumptions, despite large assumed cost advantages on a per-MIPS basis, it is found that very small systems may not match up to the cost/performance of some larger systems, when required to meet the same throughput and response-time constraints. If transactions running on smaller systems were allowed a larger response-time constraint, then it may be possible to construct a lower-cost system from smaller and less expensive processors, generally with lower supportable maximum throughput. Besides the coupling degradation between multiprocessor systems, there is a small systems effect. The cost criterion indicates that there is an optimum processor size below which total system costs would increase appreciably