UNIVERSITY OF HOUSTON
                 Department of Computer Science
                                
           COSC 4330-Fundamentals of Operating Systems
                       MIDTERM EXAMINATION
                        October 25, 1995

This exam is 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)  To  reduce  I/O costs,  we should try read or  write as  
          many useful data as possible during each disk access
         
     (b)  Processes waiting for the CPU are in the  waiting state
     
     
     
     
     (c)  The   Round-Robin   scheduling   algorithm   does   not
          differentiate   between   CPU-bound   and   I/O   bound
          processes.
  
     (d)  Most message  passing  systems  use  blocking receives.

2.   Give two methods intruders can use to modify  the  operating
     systems of the workstation on which they are logged on  (2×5
     points)  and propose the appropriate countermeasure for each
     method (2×5 points).
                     
     
     
3.   Given the following fragment of code:
     
     int fd, pd[2];
     fd = open("data", O_RDWR | O_CREAT, 0660);
     pipe(pd);
     
     redirect the standard input of the process to the file
     "data" (10 points):
     
4.   A system V scheduler  with four priority levels has the
     following table:

     #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LEVEL
         1000        0        1        2000        1   #  0
          500        0        2        2000        2   #  1
          250        1        3         200        3   #  2
          100        3        3         200        3   #  3
     
     (a)  what is the highest priority level? (5  points)
          
     (b)  would it be a good idea to replace the 1000 on the
          second line by a 100? (5 points)

     (c)  would  it be a good idea to replace  the 1 on  the
          fourth line by a 3? (5 points)

     (d)  what  happens  when a process  at priority level 1 
          has  been  in  the ready queue  for  at least  two 
          seconds? (5 points)

5.   What  is   the   major   disadvantage   of   not   using
     lightweight processes in a server? (5 points)

6.   What  are  the  major differences   between  public  and 
     private mailboxes? (10 points)

7.   What  is  the  difference between big-endian and little-
     endian machines? (5 points)




8.   What   can   we   do   to  guarantee   that   a  remote
     procedure call will be executed at most once. (5 points)




9.   What  is   the   major  disadvantage  of non-pre-emptive
     scheduling? (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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