Availability refers to the ability to use the information or resource desired. An unavailable system is as bad as no system at all. An object or service is thought to be available if;
- · It is present in a usable form.
- · It has capacity enough to meet the service’s needs.
- · It is making clear progress, and, if in wait mode, it has a bounded waiting time.
- · The service is completed in an acceptable period of time
Availability is usually defined in terms of “quality of service,” in which authorized users are expected to receive a specific level of service. The aspect of availability that is relevant to security is that someone may intentionally arrange to deny access to data or to service by making it unavailable