Date: Mon, 11 Nov 1996 17:25:13 GMT Server: NCSA/1.5 Content-type: text/html Last-modified: Wed, 06 Mar 1996 16:39:58 GMT Content-length: 2660 CS 537 - Quiz #5
UNIVERSITY OF WISCONSIN-MADISON
Computer Sciences Department
CS 537
Spring 1996
Bart Miller
Quiz #5
Wednesday, March 6

Scheduling and Synchronization

For each of the following statements, indicate whether you think it is probably true (T) or probably false (F). Then give a brief (one sentence) reason. There is not necessarily a single correct answer to each question, so your one sentence explanation is the most important part of your answer.
  1. Small time slices always improve the average response time of a system.
    Probably false: Small time slices will sometimes improve the average response of the system. If the slice is too small, the context switching time will start to dominate the useful computation time and everything (including response time) will suffer.
  2. Monitors are more powerful than semaphores, because monitors automatically provide mutual exclusion.
    Probably false: While monitors are usually more convenient to use, they are not more powerful. Since you can simulate semaphores with monitors, monitors are at least as powerful as semaphores. (Of course, you know that you can also simulate monitors with semaphores, so they actually are of equal power.)
  3. Process Control Blocks (PCBs) must be stored in the operating system kernel, where no process can access them.
    Probably true: PCBs must be in a protected part of the memory. If users (processes) were allowed to access the PCB, they could change scheduling priorities and perhaps access other processes' memory in an unintended manor.
  4. Shortest Job First (SJF) or Shortest Completion Time First (SCTF) scheduling is difficult to build on a real operating system.
    Probably true: SCTF scheduling requires knowledge of how much time a process is going to take. This requires future knowledge. You might require a user to specify the maximum amount of time that a process could run (and kill it if it exceeds this amount), then use a variant on SCTF.

Last modified: Wed Mar 6 10:39:11 CST 1996 by bart