There are two types of scalability:

  • Scale horizontally (scale out) - Scale horizontally (or scale out) means adding more nodes to a system, such as adding a new computer to a distributed software application. An example might be scaling out from one Web server system to three.
  • Scale vertically (scale up) - Scale vertically (or scale up) means adding resources to a single node in a system, typically involving the addition of CPUs or memory to a single computer.