How is scalability defined in server architectures?

Scalability in server architectures is defined as the capability of a system to handle growth, which encompasses increasing the number of connections, accommodating a greater volume of data processing, or managing more complex applications as user demands rise. This concept is critical for ensuring that a server can maintain performance and reliability when subjected to varying levels of load or when additional resources are needed.

For example, a scalable architecture can expand horizontally by adding more servers to distribute the load or vertically by enhancing existing servers with better resources like more RAM or CPU power. The focus on growth and adaptability to changing requirements is what fundamentally characterizes scalability.

In contrast, the other options discuss various aspects of performance and cost but do not capture the essence of scalability. Reducing costs as demand increases focuses on efficiency, while speed of data processing and methods for improving server speed pertain to performance optimization rather than the ability to grow and manage increased loads effectively.