Computer Science 422/622
                           Test 1 - 22 Feb - Name  ___________________

All answers must be written LEGIBLY in grammatically correct
English.  I will disregard any information which I view as illegible
or otherwise incomprehensible.  There will be NO APPEALS of my
decisions in these cases!!!

 1. Answer the following T or F:

   ____ a. Operating systems are primarily composed of software
           rather than hardware components.

   ____ b. It is the responsibility of the operating system to check
           to see if an interrupt is pending at the end of each fetch/
           execute cycle.

   ____ c. When an interrupt occurs, the instruction which is
           executed immediately after the interrupt is typically
           part of the operating system.


 2. Describe in detail how the state of the processor is altered by
    the interrupt mechanism on an 8088 and on a 370.  State
    specifically which CPU registers get new values and what
    determines where the new values come from. I DON'T care about
    how the old state of the processor is preserved here so please
    DON'T tell me about that!

    a. 8088 -






    b. 370 -






3. Consider the process state diagram on the board. For each of the
   indicated state transitions, state what causes the transition
   to occur or state that the transition does not normally occur:

   1 -



   2 -



   3 -




   4 -



   5 -



4. a. When an I/O interrupt occurs on a system such as a 370
      (in which the address of the interrupting device is stored
      at a fixed location in memory), explain how the interrupt
      handler could go about locating the Device Descriptor Block
      for the device and notifying the process which initiated
      the request that it had completed.










   b. Identify the other functions which would commonly be
      performed by I/O device interrupt service routines
      in addition to determining the final status of an I/O
      operation and passing it to the process requesting the I/O.







5. a. Identify an I/O device type which would typically be allocated
      to a process on a LONG TERM basis.






   b. What is the primary advantage of DPC mode I/O as opposed to DMA.





   c. What is the major advantage of using asynchronous interrupts
      rather than polling to determine when an I/O request completes.









6. Answer the following T or F:

   ____ a. All the devices of the same general type (e.g. disks)
           typically share the same Device Descriptor Block.

   ____ b. Most disk devices can support multiple simultaneous
           I/O operations.

   ____ c. A new device descriptor block is created each time an
           I/O request is made.


7. a. Suppose 4 jobs which each require one hour of CPU time and
      perform no I/O are submitted at the same time to be run on
      a uni-programming system (i.e. one at a time). What will
      the average turnaround time be?




   b. Suppose the 4 jobs are run concurrently using an idealized
      round robin scheduler which time preempts every second.
      What will the average turnaround time be (to the nearest
      minute?).



8. a. When a process switch is made, identify the dynamic context
      elements which must be saved and reloaded.






   b. Identify two distinct situations which must ALWAYS result in
      the dispatcher being entered regardless of the scheduling
      policies of the OS.

      1 -


      2 -



   c. Identify one other situation in which the dispatcher would
      typically be invoked but not necessarily so.




9. Identify  three common reasons for swapping a process out.

    1 -


    2 -


    3 -

10. Two desirable properties of a mutual exclusion mechanism are
    said to be safety and liveness.  Explain what is meant by
    each of these terms in this context.

    a. Safety -




    b. Liveness -




    c. Identify the condition which the following attempt at mutual
       exclusion violates and
       describe COMPLETLY the sequence of events which must occur
       for it to fail.