•How quickly a system is able to provide users with the output they require.
•For a batch system, typically is turnaround time – the length of time between submission of a job and receipt of the complete output.
•For interactive systems, the response time - the length of time between submission of an
input transaction to the system and receipt of the first character of output.
•Must be defined in terms of a unit of work and the priority categorization given to the unit of work.
•In a batch system the unit of work usually is a job.
•In an interactive system it may be a job consisting of multiple transactions, or a single transaction.