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Reliability, availability and serviceability (RAS), also known as reliability, availability, and maintainability (RAM), is a computer hardware engineering term involving reliability engineering, high availability, and serviceability design. The phrase was originally used by IBM as a term to describe the robustness of their mainframe computers.
In engineering, reliability, availability, maintainability and safety (RAMS) [1] [2] is used to characterize a product or system: Reliability: Ability to perform a specific function and may be given as design reliability or operational reliability; Availability: Ability to keep a functioning state in the given environment
In reliability engineering, the term availability has the following meanings: The degree to which a system , subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time.
High availability (HA) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. [ 1 ] There is now more dependence on these systems as a result of modernization.
For databases reliability, availability, scalability and recoverability (RASR), is an important concept. Atomicity, consistency, isolation (sometimes integrity), durability is a transaction metric. When dealing with safety-critical systems, the acronym reliability, availability, maintainability and safety is frequently used.
Availability includes non-operational periods associated with reliability, maintenance, and logistics. This is measured in terms of nines. Five-9's (99.999%) means less than 5 minutes when the system is not operating correctly over the span of one year. Availability is only meaningful for supportable systems.
In systems engineering, dependability is a measure of a system's availability, reliability, maintainability, and in some cases, other characteristics such as durability, safety and security. [1] In real-time computing , dependability is the ability to provide services that can be trusted within a time-period. [ 2 ]
Operational availability in systems engineering is a measurement of how long a system has been available to use when compared with how long it should have been available to be used. Definition [ edit ]