It is often advised to focus system design on hardware scalability rather than on capacity. It is typically cheaper to add a new node to a system in order to achieve improved performance than to partake in performance tuning to improve the capacity that each node can handle. But this approach can have diminishing returns (as discussed in performance engineering). For example: suppose a portion of a program can be sped up by parallelizing it. Suppose we can improve 70% of a module by parallelizing it, and run on four CPUs instead of one. If α is the fraction of a calculation that is sequential, and 1 − α is the fraction that can be parallelized, then the maximum speedup that can be achieved by using P processors is given according to Amdahl's Law: 
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