Homework 2

Due Oct 14, 2003

Problem 1

Readings for this problem are Chapter 33 of [RJ] and Chapter 3 of [QSP].

For a timesharing system with two disks (A and B), the probabilities for jobs completing the service at the CPU were found to be 0.80 to disk A, 0.16 to disk B, and 0.04 to the terminals. The user think time was measured to be 5 seconds, the disk service times were 30 and 25 ms respectively, and the average service time per visit to the CPU was 40 ms. Using the queueing network models discussed in class, answer the following questions.

  1. If disk A utilization is 60%, what is the utilization of the CPU and disk B?

  2. If the utilization of disk B is 10%, what is the average response time when there are 20 users in the system?

  3. What is the bottleneck device?

  4. What is the minimum average response time?

  5. What is the maximum possible disk A utilization?

  6. What is the maximum possible throughput?

  7. What changes in the CPU speed would you recommend to achieve a response time of 10 sec with 25 users? Would you also need a faster disk A or disk B?

Problem 2

Solve problem 12.6 from [RJ]. Pdf and mean only.

Problem 3

Solve problem 12.7 from [RJ].