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Reliability - The ability of a system or component to perform its required functions under stated conditions for a specified period of time.

The trustworthiness to do what the system is expected or designed to do. Reliability metrics include the following averages:

POFOD (Probability Of Failure On Demand) The likelihood that the system will fail when a user requests service. A biometric authentication device that fails to correctly identify or reject users an average of once out of a hundred times has a POFOD of 1%.

ROCOF (Rate Of Failure Occurrence) The number of unexpected events over a particular time of operation. A firewall that crashes an average of five times every 1,000 hours has a ROCOF of 5 per 1,000 hours.

MTBF (Mean Time Between Failures) The average time between unexpected events. If an IDS fails on average every 300 hours, its MTTF is 300 hours.

MTTF (Mean Time To Failure) The average time between unexpected events. If an IDS fails on average every 300 hours, its MTTF is 300 hours.

AVAIL (availability or uptime) The percentage of time that a system is available for use, taking into account planned and unplanned downtime. If a system is down an average of four hours out of 100 hours of operation, its AVAIL is 96%.

Reliability concerns quality or consistency. Most often it concerns the consistency or dependability of a measurement or service. Reliability can be found by looking for internal consistency which can be found using tests such as the split-half method, or by looking for stability, which might be measured using the test-retest method.

  • In statistics, the reliability of a set of data;
  • In experimentation, the reliability of an experiment.
  • For telecommunications, see unreliable.
  • As the theme of The Reliable Source?, reliability means the opposite of itself. In this realm, "reliability" is a positive characteristic that is attributed without regard to the actual, literal reliability of a subject. Often, subjects reliably spontaneous, inconsistent and even decidedly unreliable are celebrated for this alter-reliability. The Reliable Source? itself is reliably inconsistent in almost every aspect (save its consistent unreliability). Published irregularly by a revolving band of writers, disinterested in anything that resembles journalistic integrity, often disguised behind strange pseudonyms and all-around false aliases.
  • Reliability of a decision?

Also see these discussion threads:
"Reliability - Definition(s) (quality assurance related)"
"Reliability Definition - A Discussion thread" for further thoughts and general discussion(s) about Reliability.