CSE 5306			    Name______________________________________
 Operating Systems		    Student ID Number_________________________
 Exam 3, Summer 1997

 Please read this:
 This is a closed book, closed notes exam.
 Use a dark ink and print answers on the test paper following the question.
 Please try to keep answers together on the test page and avoid writing on the
 back of the sheets of paper.
 Turn in all pages of the test. Write your answers legibly. Unreadable answers
 will be counted wrong. Make sure you have all pages of the test.
 Read each question carefully and be sure your answer addresses the question.
 Overly general (non-specific) answers will be counted wrong.
 Point values are given for each question. The exam has a total of 100 points.

 NOTE: Some of the questions will refer to the following:
  Disk: The "spin" disk has the following characteristics:
   6 platters (12 surfaces) each has 380 tracks (numbered 0 to 379) each track
   has 64 sectors, each sector is 2 Kilobyte. Sectors are numbered 0 to 63.
   The total (raw) disk capacity is 570 Megabytes. Track 0 is the outside
   track, track to track movement takes 2 millisecs (ie track 3 to 5 takes 4 ms)

 1. [	pts]
  a.) In Apple MAC OS the file system identifies the "type" of each file:
      pictures, text, executables, etc. 1. How does UNIX do the same (identify
      which files are pictures, text, executable, etc.)? 2. How can (should)
      each OS support a new file type (like video with sound - VIDS) and
      3. list an advantage of each method (or 2 advantages if the same method)
    1.



    2.



    3.




  b.) The OS.5 uses an "access matrix" for protection. When a users application
      program wants to print to a physical printer the application calls a
      runtime library routine which interfaces to a printer deamon (task) which
      queues print jobs and allows for "print control" (killing jobs, etc.)
      which finally allows data to be sent to the printer. 1. In this scheme
      describe the access matrix entries (in general) what do rows and columns
      represent and 2. what does each entry represent? 3. What are an advantage
      and disadvantage to using "access matrix" rather than the way UNIX does
      protection?
    1.



    2.


    3.



  c.) In the OS.99 several processes may open and read or write from the same
      file concurrently but changes made by a process may only be seen when that
      process closes the file and another process later opens the file.
      1. What is this technique (issue) called? 2. If not the same, what does
      UNIX do in this situation?





 2. [	pts]
  In programming assignment 4 (File Gather) you implemented a new, simple,
  file system.
  a.) Identify and briefly describe the "disk" space allocation method.





  b.) Identify 2 other disk space allocation methods, and give an advantage of
      each as compared to part a.)
      1.



      2.



  c.) What is the "logical" equivalent to the disk boot block (or UNIX "super
      block") and what part (if any) is necessary for your program? Why?





  d.) Due to an attack on your file system (or a programming error) some blocks
      are pointed to (part of) two different directory entries. Some used blocks
      are also marked as free. 1. What type of tool (if such could exist) could
      "repair" (fix) your file system? 2. Very briefly describe how it could
      work (or why it can not).






  e.) Describe how a virus could attack your assignment 4, 1. where could it
      "hide" and how? 2. Could the virus be spread, and how?








  f.) To prevent any security "attacks" on your assignment 4, you require each
      user to setup and use a password. The "root" password is hardcoded and
      not changeable but is a 30 character random mixture of letters and
      numbers. Each user sets her own password, minimum 20 characters, which
      must be changed every week. 1. You have created a potential security
      problem, what is it called, describe it, why is it a problem?
      2. What minor change this method would be more secure and why?





  g.) One of the problems with the implementation of assignment 4 is that there
      are several file size limits. 1. In one case only a few characters can
      occupy an entire file system. Describe how this can occur and what (if
      anything) can be done to improve the situation. 2. What is the maximum
      size of a file that can fit in this FS? Could anything be done to improve
      this limit?





  h.) 1. Identify and describe what type of directory structure in assignment 4:
      (for example, "acyclic graph") 2. Assuming a linear directory, in what
      cases is this an advantage and when is it a disadvantage?




 3. [	pts]
  A system uses the "spin" disk.
  We are currently reading on track 88, sector 20 (before that we were writing
  track 110, sector 32). The request queue, in arrival time order is:
  (track 180, sector 22), (track 80, sector 58), (track 92, sector 60)
  How much time would EACH of the disk scheduling algorithms take for the data
  given: (please show your calculations):
  FCFS	=


  LOOK (SCAN with look) =


  SSTF	=




 4. [	pts]
  a.) Is X-Windows most appropriate in a LAN, WAN, or direct terminal? Why?







  b.) Sometimes it is better to view an X_window application as a small OS
      because of call back routines, etc. Describe how (and why) this X-windows
      interface is like an OS.






  c.) At what layer of the network protocol does a WWW browser run, if it
      depends on X-Windows for graphics, keyboard, mouse, etc. support? Why?




  d.) Briefly, describe the difference between connection schemes and routing
      in a network. Give 2 examples of each.