What is Scalability?
The number of simultaneous requests that an application can successfully support is a measure of its scalability. The point at which an application can no longer successfully handle more requests is its scalability limit. When a key piece of hardware is exhausted and new or more machines are needed, this limit is reached. Scaling these resources can include any combination of CPU and physical memory (different or more computers), hard disc (larger hard drives, less "live" data, solid state drives), and/or network bandwidth (several network interface controllers, larger NICs, fibre, and so on).