Two metrics for defining computer performances

1. Response time
   • The time between the start and completion of a task
   • related to single task
   • e.g., how long it takes to do a single task
2. Throughput
   • A total amount of works done per unit time
   • related to multiple tasks
   • e.g., tasks per hour

Q. If we replace the processor in a computer with ad faster version

• Response time decrease
• Throughput increase

Q. If we add more processors to a system

• Response time maintain or increase (more lanes more complex)
• Throughput increase

Defining performance

• $Performance = \frac{1}{execution\;time\,(reponse\;time)}$
• Relative performance: X is N time faster than Y
• $\frac{Performance_x}{Performance_y} = \frac{Execution time_y}{Execution time_x} = N$

• Elapsed time = system performance = t1 + t2 + t3 + t4
  • total time between the start and completion of a task, including everything
• CPU time = CPU performance = t1 + t4 (Only this in this class)
  • The time spent processing a given task on a processor

The CPU time can be further divided into

• User CPU time
  • spent for processing the code of the program (some functions)
• System CPU time
  • spent in the operating system performing tasks for the program (OS)