Reliability vs. Availability

June 1997 / International Features / European Telecoms Brace for Change / Reliability vs. Availability

Reliability and availability are two important aspects of the performance of any service or system. Reliability implies that the system performs its specified task correctly (e.g., a calculator al ways delivers the right answers). Availability means that the system is ready for immediate use.
As is so often the case in engineering, these two qualities must often be traded off against one another. For example, a Formula One racing car must be reliable to win races, but is not very available as it spends more time in the workshop than on the track. An air-traffic-control system requires the maximum degree of reliability and availability that can be achieved.
In a telecoms OS, availability must take precedence over reliability, as withdrawal of service will not be tolerated by users. Mechanisms such as the hot-swapping of hardware components and the hot-restarting of software offer ways to maximize availability in the face of only moderately reliable components.

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Matthew Wilson
My approach to software engineering is far more pragmatic than it is theoretical--and no language better exemplifies this than C++.

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