Scalability is the ability of a system to accomplish more work while maintaining the quality (i.e., without degradation) of the products produced or services provided by the system. There are different ways to calculate the work produced or performed by the system, which usually depends on the kind of product produced or services rendered.
For software systems, here are some of the common metrics used to quantify the products produced or the services provided:
Scalability is about being able to increase the output of products and services without major disruptions, interruptions or increased costs. Often, because of the Economies of Scale, the estimates for the costs should actually decline.
Two valid approaches to achieve Scalability are: