Availability - the ability of an IT service or other configuration item (CI) to perform its agreed function when required.

Availability is determined by:

  • Reliability
  • Maintainability
  • Serviceability
  • Performance
  • Security

Reliability - a measure of how long IT service or CI can perform its agreed function without interruption.

Maintainability - a measure of how quickly and effectively an IT service or CI can be restored to normal working after a failure.

Serviceability - the ability of a third party supplier to meet the terms of its contract.

High availability - a charachteristic of the IT service that minimizes or masks the effects of IT component failure to the users of a service.

Fault-tolerance - the ability of an IT service, component or CI to operate correctly after failure of a component part.

Continuous operation - an approach to eliminate planned downtime.

Continuous availability - an approach to achieve 100% availability.