COSC 4330                   MIDTERM                         10/14/1999

Closed Book.   You can have one sheet of notes.

1.  For  each  of  the  statements below, indicate  in  one  sentence
    whether the statement is true or false (2 points), and why
    (3 points).
     
    (a)  Disk drive access times have been doubling every year for the
         last two or three years.

	 FALSE, they have actually decreased 

    (b)  To reduce I/O costs, we should try read or write as many useful
         data as possible during each disk access

         TRUE, we will need less disk accesses to get the same amount
	 of data

    (c)  A system without privileged instructions cannot be made safe.

         TRUE,  user programs can directly access disk drives

    (d)  In a master/slave multiprocessor organization, there can be
         several copies of the kernel running at the same time.
    
	 FALSE, the master processor is the only one on which the
	 kernel can run.

    (e)  Most scheduling policies decrease the priority of processes
         that have exhausted their slice of CPU time.

	 TRUE, other processes are favored.
    
    (f)  In BSD UNIX, the priority of a process is function of its past
         CPU usage.

	 TRUE.

2.  Answer  in one sentence to each of the following questions:  (4*5
    points)
     
     (a)  What is the major disadvantage of microkernels?
     
	  Each system call involving a user-level server will require
	  four context switches instead of two.

     (b)  How does the System V.4 scheduler prevent process
          starvation?

          It changes the priority of processes that waited more
	  than the maximum waiting time for their priority level.

     (c)  What is the major advantage of kernel-supported threads?

          They do not block the whole task when a thread is doing a
	  blocking system call.

     (d)  When should we worry about the ordering of bytes inside
          words?
          
	  In remote procedure calls between to different machines.

3.   A good scheduling policy should (a) be fair,  (b) minimize
     response time for interactive users, and (c) maximize system
     throughput.  How does the round robin policy fare with respect
     to these three criteria (3x5 points)?

     (a)  round robin is fair as it does not favor any type of processes

     (b)  round robin can provide a low response time for interactive
          users by using a small time slice

     (c)  round robin cannot provide at the same time a small response
	  time for interactive users and a good system throughput as
	  a small time slice involves too many context switches.

4.   What would be the major disadvantage of using non-blocking receives
     to build a server? (5 points)

     The server would have to do busy waits.

5.   How many processes will the following program fork? (5 points)?

     main(){
          fork(); fork(); fork();
     }
                         The program will fork _____7______ processes.
			      (not counting the original process)
                                                                      
6.   List the three state transitions bringing a process into the
     ready state and indicate what events can cause them (3x5 points)
     
     --  returning from the RUNNING state after a timer interrupt or the
	 arrival of a higher priority process
     
     --  leaving the WAITING state once a system request has been
         completed

     --  returning from the READY-SUSPENDED state

7.   What would be the effect of executing the following program
     fragment? (10 points)
     
          int pda[2]; int pdb[2];
          pipe(pda); pipe(pdb);
          close(2);
          dup(pdb[1]);
          close(0);
          dup(pda[0]);

	  The program will read its standard input from pda[0]
	  and redirect its standard error to pdb[1].