While computers with tens of thousands of processors have successfully delivered high performance power for solving some of the so-called “grand-challenge” applications, the notion of scalability is becoming an important metric in the evaluation of parallel machine architectures and algorithms. In this study the prediction of scalability and its application are carefully investigated. A simple formula is presented to show the relation between scalability, single processor computing power, and degradation of parallelism. A case study is conducted on a multi-ring KSR-1 shared virtual memory machine. Experimental and theoretical results show that the influence of topology variation of an architecture is predictable. Therefore, the performance of an algorithm on a sophisticated hierarchical architecture can be predicted and a good algorithm-machine combination can be selected for a given application.