The Performance of any particular system is determined by carefully analysing certain performance measures like Response Times, Throughputs and Utilizations. These measures can be obtained as ouputs of performance models.
It is the average time interval elapsed between the instant a transaction is submitted to the system for processing until the answer begins to appear at the user's terminal.
It is the average number of transactions or jobs executed per unit time. In other words, it is the rate at which requests are serviced.
It is the percentage of time the device is being used, during a given time interval. A device is said to be saturated if its utilization approaches 100%.