UNIVERSITY OF HOUSTON
                 Department of Computer Science

                   COSC 6360-Operating Systems
                             MIDTERM
                        October 31, 1989

Be concise but complete.

1.   How does UNIX handle disk writes? (4 points)  What  are  the
     advantages and disadvantages of this approach? (4 points) Do
     they have equal importances in all  computing  environments?
     (2 points)

2.   Describe the page replacement policy used by the most recent
     releases of Berkeley UNIX. (10 points)

3.   What is a superblock? What data structures does it  contain?
     (4  points) What happens if a superblock becomes unreadable?
     (2 points) What does Berkeley UNIX to avoid this occurrence?
     (4 points)

4.   How many Active Segment Tables do concurrently  exist  in  a
     typical  MULTICS  system?  (3 points) Where and how are they
     stored? (7 points)

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

5.   A modern revival of the MULTICS segmented architecture would
     probably  allow  much larger segments, say up to a Gigabyte.
     What would be the major impact of this change on the  imple-
     mentation of the MULTICS virtual memory? (10 points)

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6.   What is copy-on-write? (3  points)  For  what  purpose  does
     ACCENT  use  this  technique? (3 points) Was it a good deci-
     sion? (4 points)

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     THE READING LIST; COPY-ON-WRITE IS ALSO A FEATURE OF MACH
     
7.   Describe the data structures used by ACCENT  to  handle  the
     virtual to real address translation. (10 points)

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8.   Why did Hoare introduce guarded commands in CSP? (5  points)
     How  does  Berkeley  UNIX  IPC  solves  the same problem? (5
     points)

9.   Enumerate the three conditions under which  a  monitor  pro-
     cedure relinquishes its control of the monitor? (10 points)

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10.  What distinguishes transactions from remote procedure calls?
     (10 points)
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