UNIVERSITY OF HOUSTON
                 Department of Computer Science
                                
          COSC 4330--Fundamentals of Operating Systems
                        FINAL EXAMINATION
                          July 23, 1994

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

1.   Describe a scheduling policy that provides a fast response
     time  for interactive processes while  controlling
     the context switch overhead. (10 points)

2.   You  are  participating to a humanitarian  rescue operation
     and have to distribute 50,000 pairs of sandals  to a  huge crowd
     of refugees.  It just happened that the 50,000 left sandals and
     the 50,000 right sandals have arrived at different places and you
     have no way to move them to a single location.   Since there are
     not enough sandals for everyone, one may fear that many refugees
     will receive  a left sandal but no right sandal and vice versa.
     
     (a)   What can be done to prevent this situation?  (5 points)
     
     (b)   What  necessary condition for deadlocks would be denied by
           your solution? (5 points)?
          
3.   (a)   What is the difference between segmentation and paging?
           (10 points)

     (b)   Which of these two techniques is easier to implement and
           why? (5 points)
     
4.    What is a Translation Lookaside Buffer? (10 points)  What
      constitutes a good hit ratio for a TLB and why? (5 points)
     
5.   When a page is expelled from the main memory, how can the page
     fault handler know if the expelled page must be written back to
     disk before being overwritten?  (10 points)

6.   Describe two page replacement policies that do not require any
     special hardware but provide nevertheless a good performance.
     (20 points)
     
7.   Describe in some detail the data structures used by UNIX to
     store files on disk assuming that the block size of the file
     system is 512 bytes. (10 points)

8.  It has been said that the UNIX file system uses at the same time
    access control lists and tickets to protect its file.  What are
    the UNIX entities playing the role of:
     
     (a)  an access control list? (5 points)

     (b)  a ticket? (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.
----------------------------------------------------------------