Degree to which a system, product or component performs specified functions under specified conditions for a specified period of time. This characteristic is composed of the following sub-characteristics:
- Faultlessness - Degree to which a system, product or component performs specified functions without fault under normal operation.
- Availability - Degree to which a system, product or component is operational and accessible when required for use.
- Fault tolerance - Degree to which a system, product or component operates as intended despite the presence of hardware or software faults.
- Recoverability - Degree to which, in the event of an interruption or a failure, a product or system can recover the data directly affected and re-establish the desired state of the system.