Operating Systems
Exam 3
May 20, 1999

Instructions:
  1. Put your name and student number on the exam books now.
  2. The exam is closed book and closed notes.
  3. You have 2 hours to complete the exam.
  4. First read the entire exam and budget your time accordingly. Be a smart test taker, if you get stuck on one problem go on to the next.
  5. Show your work. Partial credit is possible, but only if you show intermediate steps.
  6. Good luck.
  1. (20 pts) Short Answer.

    1. (5 pts) What type of naming scheme does the web use and what advantage does it have?

    2. (5 pts) What does RPC stand for and how does it work?

    3. (5 pts) Name the four components of disk access time.

    4. (5 pts) What are the differences between user threads and kernel threads?

  2. (20 pts) Distributed System Design. Design a web caching mechanism where the main design objective is fast local access time, include policies for consistancy, fault tolerance, and how and when to store your web-cache in memory and on the local disk.

  3. (20 pts) Write Policies. Compare write back and write through policies on a uniprocessor using the following criteria:

    1. Speed
    2. Consistency
    3. Fault tolerance
    4. Complexity

    Does your solution still apply in a distributed system? Why or why not?

  4. (20 pts) Semaphores. In this problem, we have 3 teams: red, green, and blue. Each team gets a turn in the order red, green, blue, red, green, blue and so on. Enforce the schedule using semaphores(s). Note that many team members of the same color may want to take a turn; model each as an independent process.