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(COMP252)midterm00F_sol.pdf
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COMP 252 Principles of Systems Software
Fall Semester 2000
Midterm Examination
Date: October 21, Time 5pm : 7pm
Name:___SOLUTION_________Student ID:________________Email:_______________
Instructions:
1.
This is a closed book/notes exam. Dont discuss the exam questions with your colleagues during the exam.

2.
This examination paper consists of 7 pages and 6 questions.

3.
Please write your name, student ID and Email on this page.

4.
For each subsequent page, please write your student ID at the top of the page in the space provided.

5.
Please answer all the questions within the space provided on the examination paper. You may use the back of the pages for your rough work.

6.
Please read each question very carefully and answer the question clearly and to the point. Make sure that your answers are neatly written, readable and legible.

7.
Show all the steps you use in deriving your answer, where ever appropriate.

8.
For each of the questions assume that the concepts are known to the graders. Concentrate on answering to the point what is asked. Do not define or describe the concepts.


Question Points Score
1 15
2 20
3 15
4 10
5 20
6 20
TOTAL 100

1. a) What does SPOOLING stand for ? Describe the SPOOLING operation and the advantage of doing this. (5 points)
Answer: SPOOLING is Simultaneous Peripheral Operation On-line. The disk is used as a large buffer for reading ahead on input devices and for storing output files until the output devices are able to accept them. SPOOLING allows overlap of the I/O of one job with the computation of other jobs and improve system throughput.
b) What does DMA stand for ? Describe the DMA operation and the advantage of doing so. (5 points)
Answer: DMA stands for Direct Memory Access. Data are directly transferred between main memory and the input or output device one block at a time. The CPU is interrupted only after the entire block has been transferred instead of one character at a time. It reduces the overhead of the CPU in handling I/O interrupts so it can spend more time on computation.
c) What is a zombie process ? (5 points)
Answer: A zombie process is a child process that has exited but not yet acted upon by its parent process with the WAIT system call. Its state is maintained by the operating system but it is considered dead otherwise (i.e., cannot run or compete for system resources).
2. a) In the Client-Server Model of operating system structure, most of the traditional operating system functions are implemented as servers running in the user mode. i) name two advantages of doing so; (6 points)
Answer: -implementing each function as a separate server allows modularity and is easier to do as it enables the implementor to focus on one function at a time.
- debugging in the user mode is easier as one can use the existing debugging tools
-an error in a server in the user mode m