UNIVERSITY OF HOUSTON
                 Department of Computer Science
          COSC 4330-- Fundamentals of Operating Systems
                         SECOND MIDTERM
                         March 30, 1994

This exam is closed book.  You can have one sheet of notes.

1.   What is  the  major  disadvantage  of  Conditional  Critical
     Regions?  (10 points)

2.   What is the difference between  a  blocking  receive  and  a
     non-blocking  receive?  (10 points) . Which one can be simu-
     lated by the other and how? (10  points)  

3.   A  binary semaphore is  a semaphore  than  can only have two
     values, zero and one. Write the two monitor procedures neces-
     sary  to implement a binary semaphore  assuming  (a) that an
     up operation on a binary semaphore that is already equal  to
     one does nothing and (b) that the initial value of the sema-
     phore is one.  (2X10 points).

     /* declare here your global variable(s) */

     /* the only condition you will need */
     condition go;

     /* up function */
     up (){

     } /* up */

     /* down function*/
     down () {

     } /* down */

     How would you initialize your semaphore? ( 5 points)

4.   What can be done to reduce message transfer costs when  both
     the  sender  and  the  receiver processes reside on the same
     machine?  (10 points)

5.   How can you explain the fact that the throughput of  a  com-
     puter  using a Round-Robin scheduling policy often goes down
     when the number of interactive users goes up?  (10 points)

6.   Why is it a good idea to give larger slices of CPU  time  to
     processes with lower priorities?  (10 points)

7.   True or False:  (3X5 points)

     T     F 
       ---   ---
          All UNIX message passing primitives use direct naming

     T     F 
       ---   ---
          In a RPC, one of the tasks of the user stub is to  wait
          for messages from user processes

     T     F 
       ---   ---
          Multiprogramming  is  especially  beneficial  when  the
          workload contains I/O-bound processes


--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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