Availability
Availability is the degree to which a system or component is operational and accessible when required for use.
“The degree to which a component or system is operational and accessible when required for use.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Availability?
Availability measures whether users can successfully access a system during expected operating periods. High availability minimizes downtime and supports reliable business operations.
Reliability relationship: Reliable systems contribute to higher availability but are not identical concepts.
Factors affecting availability: Hardware failures, software defects, maintenance, and network issues can reduce availability.
Testing focus: Availability testing verifies system behavior during failures, recovery, and prolonged operation.
Real World Example
A national travel service is preparing for a public holiday sale where thousands of users may search, reserve, and pay for tickets at the same time.
A feature that works for one tester may fail under traffic, resource pressure, or infrastructure disruption. Availability helps the team focus on behavior under operational conditions.
The tester defines realistic traffic, failure, and recovery situations, then watches response time, errors, data consistency, and whether users can continue critical actions.
The release decision improves because Availability gives stakeholders evidence about service behavior when demand or disruption is no longer theoretical.
Practice Questions
Question 1
Which test MOST directly evaluates availability?
Question 2
Which metric MOST closely reflects availability commitments?
Test your knowledge with real ISTQB-style questions
You’ve learned Availability. Test your understanding with topic-specific questions in our Mock Exams.