Availability as the Most Significant Contributor to TCO
Experience with information systems has shown us that the user requirement responsible for the greatest hidden costs is availability. This user requirement takes precedence over all others: What good is a system if it's unavailable? Availability also requires ongoing management and maintenance throughout the entire life of every system.
A system is considered available when users can work with it without experiencing outages. Availability is measured from the user's point of view. It deals not only with the prevention of real system outages, but with user-perceived outages as well. These perceived outages are anything that prevents the user from working with the system productively, such as prolonged response times, lack of assistance, or lack of available workstations. As long as the user doesn't perceive or feel the outage, the system is considered "available."
A user will consider a system unavailable if one of these conditions occurs:
The system is not accessible. If the user can't access the resources he or she needs to run an application, the system is considered unavailable. The system is equally unavailable if all workstations or software licenses are in use, or if the network connection to necessary data is down, or if the system has a virus infection.
The system is running too slowly. The system may be operational, but if the response time is long the user will give up waiting and consider the system as unavailable.
The system is intermittently having problems. The user will choose not to use a system if he or she suspects that work may be lost due to intermittent system failures.