UNIVERSITY OF HOUSTON
               Department of Computer Science

                COSC 6360: OPERATING SYSTEMS
                         MIDTERM A

                       March 18, 1993

CLOSED BOOK You may have with you two sheets of notes.

1.   What is the effect of setting the SET-USERID bit  of  a
     UNIX file ON? (10 points)

2.   UNIX has a rather unusual way to fork  another  process
     in  the  sense  it  uses  two  system calls--fork() and
     exec()--instead of specifying in the  fork()  call  the
     name  of  the  file  to be executed.  What is the major
     advantage of this two step approach? (10 points)

3.   Describe the two mechanisms used by the  Ninth  Edition
     UNIX System to construct "flexible and general routines
     to connect local and remote processes." (2x10 points)

     THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN THE
     READING LIST.  IT WILL BE NOT BE ASKED AGAIN.

4.   How many instances of the following data structures are
     normally  present in a MULTICS system?  The four possi-
     ble answers are (a) one instance for the whole  system,
     (b)  one  instance  per  process,  (c) one instance per
     active segment, and (d)  more  than  one  instance  per
     active segment.

     descriptor segment:   (a)(b)(c)(d)

     known segment table:  (a)(b)(c)(d)

     active segment table: (a)(b)(c)(d)

     page table:           (a)(b)(c)(d)

     linkage section:      (a)(b)(c)(d)

     (5x4 points)

     THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN THE
     READING LIST.  IT WILL BE NOT BE ASKED AGAIN.

5.   How does MACH implement the UNIX  fork  operation?  (10
     points)

6.   What is an INVERTED page table? (5 points)  Why  is  it
     harder  to  implement SHARED PAGES on a system using an
     inverted page table?  (5 points)

7.   What is needed to implement the AT MOST ONCE  semantics
     in a remote procedure call mechanism? (5 points)

8.   What does Birrell and Nelson's implementation of RPC to
     allow  servers  to eliminate duplicate call packets? (5
     points)

9.   What does LRPC to reduce argument copying? (10 points)