UNIVERSITY OF HOUSTON
                 Department of Computer Science

          COSC 4330: Fundamentals of Operating Systems
                       MIDTERM EXAMINATION
                         October 7, 1993

CLOSED BOOK: You are allowed one 8.5 by 11" sheet of notes.

1.   Given the declaration char text[80][24];
     how do you pass the array textby reference  to  a  procedure
     called firstnum()? (5 points)

2.   What is the difference between a uniprogramming and  a  mul-
     tiprogramming system? (10 points)

3.   How are system calls implemented on most machines  having  a
     user mode and a supervisor mode? (10 points)

4.   You are hired as consultant by the  ACME  Computer  Company.
     They  have just discovered that timer interrupts do not work
     on their new microprocessor chip.  They ask you whether they
     will be ever able to build a decent timesharing system using
     their new chip?  Justify your answer.  (20 points)

5.   Show how an instruction such as RSW r1,r2  which  swaps  the
     values  of  the two registers r1 and r2 can be used to solve
     the mutual exclusion problem. (20 points)

6.   What are the two possible correct values for a mutual exclu-
     sion semaphore? (5 points)

7.   What are the possible outcomes of a DOWN operation  executed
     through a semop() system call? In which states will the pro-
     cess be left?  (10 points)

8.   Explain why the following solution to the  mutual  exclusion
     problem does NOT work. (20 points)

           int lock one, lock two;
             ...
        process one {                process two{
           for (;;) {                   for (;;) {
              lock one = 1;                lock two = 1;
              while (lock two);            while (lock one);
              crit sect                    crit sect
              lock one = 0;                lock two = 0;
              other stuff                  other stuff
            }                           }
        }/* one*/                    } /*two*/

--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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