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) THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN THE READING LIST. IT WILL BE NOT BE ASKED AGAIN. 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) THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN 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) THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN THE READING LIST. IT WILL BE NOT BE ASKED AGAIN. 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) THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN THE READING LIST. IT WILL BE NOT BE ASKED AGAIN. 10. What distinguishes transactions from remote procedure calls? (10 points) THIS QUESTION WAS RELATED TO A PAPER THAT IS NOT ANYMORE IN THE READING LIST. IT WILL BE NOT BE ASKED AGAIN.