UNIVERSITY OF HOUSTON
                 Department of Computer Science
                                
           COSC 4330-Fundamentals of Operating Systems
                        FINAL EXAMINATION
                        December 11, 1996

This exam is closed book.  You can have one sheet of notes.
     
1.   Give one good reason for implementing an all or nothing
     semantics in remote procedure calls? (5 points)

2.   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) Deadlocks cannot happen without a circular wait condition.

     b) Dynamic address translation is normally done by the kernel.

     c)  All virtual memory systems have a PAGE-REFERENCED bit.

3.   Add the missing parts to the following monitor, to obtain a
     solution for the readers/writers problem. (5×4 points)

     monitor readers_and_writers {

     // visible part
          read_lock();
          write_lock();
          read_unlock();
          write_unlock();
          
     //invisible part
          int inuse, readerscount;
          condition green;
          
          read_lock()
          {
               if (inuse == 1 &&________________________)
                    green.wait;
               readerscount++;
               inuse = 1;
               green.signal;  //let another waiting reader in
          } //read_lock
          
          write_lock()
          {
               __________________________
                    green.wait;
               inuse = 1;
          } //write_lock
          
          read_unlock()
          {
               readerscount--;
               if (______________________){
                    inuse = 0;
                    _________________;
               };
          } // read_unlock
          
          write_unlock()
          {
               _________________;
               inuse = 0;
          }// write_unlock
          
          body()
          {
          readerscount = inuse = 0;
          }

     } //monitor readers_and_writers

4.   A workstation has a maximum memory size of 256 Megabytes.  The
     memory is byte addressable and virtual addresses have 32
     bits, 21 of which are dedicated to the page number: (2×5
     points)
     
     a) what is the page size?                          ______ bytes
       
     b) what is the size of a process virtual address space?
                                                    __________ pages

     You may detail here your computations for partial credit:
     
5.   What are the main advantage and the main disadvantage of the
     three following page replacement policies (6×5 points)
     
     a)   LRU:

          main advantage:

          main disadvantage:
 
     b)   Working Set:

          main advantage:

          main disadvantage:
     
     c)   VMS:

          main advantage:
               
          (I can think of two but one is very specific to the VMS
          policy.)
          
          main disadvantage:
       
6.   What are the two criteria to consider when selecting a block size
     for  a  file  system?  (2×3 points)  How does Berkeley  UNIX
     solve this dilemma? (4 points)
     
7.   Explain  how the UNIX file system implements access  control
     lists (6 points)  What would be the main advantage and the main
     disadvantage  of  a fuller implementation  of  the  concept?
     (2×2 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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