COSC 4330                    3/3/97            NAME: _________________

                      UNIVERSITY OF HOUSTON
                 Department of Computer Science
                                
           COSC 4330-Fundamentals of Operating Systems
                       MIDTERM EXAMINATION
                          March 3, 1997

This exam is closed book.  You can have one sheet of notes.
     
1.   For each of the statements below, indicate whether the
     statement is true or false (2 points each) and explain why in one
     sentence (3 points each):
     
     a)   Server processes normally run in privileged mode.
       
     b)   Single-user systems do not need memory protection.

     c)   Adding user-level threads to an operating system does not
          require any modifications to the kernel.

     d)   A time-sharing system is a special case of a real-time
          system.

2.   You are hired as a consultant to work on a new microkernel-
     based operating system.  Your new employers tell you that the
     system is too slow and ask you to make it faster.  They add they
     have already tried everything possible to reduce the context
     switch time and speed up interprocess communication.

     a)   What else could you suggest? (5 points)
         
b)   Somebody at a meeting calls your suggestion a "Crazy idea."
     What can you say to show that your idea is not as crazy as it
    appears?  (5 points)

3.   Under which two possible conditions can a process return
     from the running state to the ready state?  (2×5 points)  Which
     of these two conditions should increase or decrease the priority
     of the process and why?  (5 points)

4.   Consider the following program:
     
     main(){
          int pid, count;
          count = 0;
          if ((pid = fork()) == 0) {
               count++;
               printf("Count is equal to %d\n", count);
               exit(0);
          }
          while (wait(0) != pid);
          printf("Count is now equal to %d\n", count);
     } /* main */
     
     What will be the two lines printed by the program:

     a)   if the fork() and wait() statements refer to regular UNIX
          processes?  (5 points)
       
     b)   if they refer to lightweight processes?  (5 points)
 
5.   How will the following piece of code affect stdin, stdout
     and stderr?  (5 points each)
     
          int fd, pd[2];
          pipe(pd);
          fd = open("data.txt", O_RDWR | O_CREAT, 0640);
          close (0);
          dup(fd);
          close(2);
          dup(pd[1]);
     
     stdin is
     
     stdout is
     
     stderr is

6.   Why would it be impossible to write a server using blocking
     reads and direct communication?  ( 5 points)  What is the best
     alternative?  (5 points)

7.   What are the two advantages of multilevel scheduling
     policies over the round-robin policy?  (2×5 points)  What’s their
     only major disadvantage?  (5 points)

8.   What are the two advantages of multilevel scheduling
     policies over the round-robin policy?  (2×5 points)  What’s their
     only major disadvantage?  (5 points)
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

--IMPORTANT----IMPORTANT----IMPORTANT----IMPORTANT----IMPORTANT--
Please do not try to answer these questions by yourself BEFORE
having a clear idea of what's on the test for which you are
studying.

Materials covered in each test DO VARY from semester to semester
because the pace of the course can change, some materials are be
added and other deleted almost every semester.
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