Horizontal Scaling

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To scale horizontally (or scale out) means to add 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. As computer prices have dropped and performance continues to increase, low cost "commodity" systems have been used for high performance computing applications such as seismic analysis and biotechnology workloads that could in the past only be handled by supercomputers. Hundreds of small computers may be configured in a cluster to obtain aggregate computing power that often exceeds that of computers based on a single traditional processor. This model was further fueled by the availability of high performance interconnects such as Gigabit Ethernet, InfiniBand and Myrinet. Its growth has also led to demand for software that allows efficient management and maintenance of multiple nodes, as well as hardware such as shared data storage with much higher I/O performance. Size scalability is the maximum number of processors that a system can accommodate.