System availability quantifies the extent to which a system is available as required, when required. The concept applies to all systems, from IT systems to production systems to communications systems.
The simplicity of this availability metric – essentially, the percentage of required time during which the system is functioning as required – is in stark contrast to the complexity of managing service and maintenance. For example, the elevator system in a hotel must be available at all times. However, when there are multiple elevators, not all elevators need to be available during periods of low usage. So a rolling program of maintenance can maintain 100% availability even though it takes some elevators out of service at certain times.
System Average Interruption Duration Index (SAIDI) is the average number of hours of service interruption experienced by each customer in one year. Widely used by electricity distribution organizations, it is often used alongside System Average Interruption Frequency Index (SAIFI) to distinguish many short interruptions from a few longer interruptions.
The US Energy Information Administration collects SAIDI and SAIFI data for three categories of electricity distributor – municipals (owned by cities), co-ops (owned by members); and investor owned (owned by shareholders). In 2016, municipals’ customers experienced the lowest SAIDI and SAIFI of the three categories.
System on Chip (SOC) is a type of integrated circuit where all of the components of a system (such as a computer) have been combined on a single chip. This may include distinct functions and technologies such as analogue, digital and radio frequency circuitry.
Systems Integration (SI) is the discipline of combining separate computer (and physical) systems to act as a single co-ordinated whole. In Aerospace and Automotive, for example, OEMs are called systems integrators because their expertise is less and less in research and development (R&D), and more in assembling pre-built supplier systems using highly efficient manufacturing processes in their own factories.