COSC 4330                    FINAL                            12/14/99

Closed Book.   You can have one sheet of notes.

1.  For  each  of  the statements below, indicate  in  one  sentence
    whether or not the statement is true or false, and why (5 points
    each):
  
    a)  There are some problems that can be solved using monitors and
        cannot be solved using semaphores.

	 FALSE.  You could if you wanted implement semaphores on the
         top of monitors

    b)   Memory protection is always done by the computer hardware.

	 TRUE. This is the only way to do it fast enough.

    c)   We can prevent deadlocks in message-passing systems by denying
         the hold-and-wait condition.
	
	 FALSE. This would require each process to receive all its
         messages at once.

    d)   We can prevent deadlocks in message-passing systems by denying
         the mutual exclusion condition.

	 FALSE.  This would require processes to "receive" messages that
         were not yet sent.

2.  A computer has 512 Megabytes of main memory, 32 bit addresses and
    a page size of eight kilobytes.
  
    a)   How many page frames are there in main memory?  (5 points)

         __ 2^(29-13) = 2^16 = 64K ______  frames
     
    b)   How many bits are there in the page offset?  (5 points)

         __ 13 __  bits (because 2^13= 8K)

3.  Complete the following monitor code to implement a binary
    semaphore.  (20 points)
  
  Class binary_semaphore {
       private condition go;
       private int a;
       
       public void synchronized P(){
            _ if (a == 0) _______
            _____ go.wait;  _____
            a = _ a - 1 _;
       } // P
       
       public void synchronized V() {
            a = _ 1 _;  // THAT'S WHAT MAKES IT A BINARY SEMAPHORE
            go.notify;
       } // V
       
       binary_semaphore(){
            a = 0;
            _____________________
       } //constructor
     } // Class semaphore

4.  Given the six following page replacement policies:

    Global FIFO        Clock          Denning's Working Set
    Global LRU         OPT            VMS

    indicate the policy or the policies:

    a) that performs worse than all other five policies
       (5 points): Global FIFO

    b) that handle real-time processes best (5 points): VMS

5.  Given the following result for the "ls -lg a.ps"
    Unix command

    -rw-r-----  1 paris    faculty    341993 Dec 13 18:23 a.ps

    a)  which users can modify the file Universal.ps? (5 points)
        paris

    b)  which users can read it? (5 points)

        paris and all members of the "faculty" group

6.  What are the major advantage and disadvantage of the VMS
    page replacement policy?  (10 points)

7.  A Berkeley UNIX file system has 16 kilobyte blocks.  How many
    bytes of any given file can be accessed:
  
    a)  directly from the i-node (5 points):       ________ bytes
     
    b)  with one level of indirection (5 points):  ________ bytes

    c)  with two levels of indirection (5 points): _______  bytes
     
     
8.  What is the difference between internal fragmentation and
    external fragmentation? (5 points)