CS代考 COMP3231/COMP9201 Operating Systems

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THE UNIVERSITY OF NEW SOUTH WALES Final Examination
COMP3231/COMP9201 Operating Systems

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• Time allowed: 2 hours
• Reading time: 10 minutes
• Total number of questions: 6
• Answer all questions
• The questions are not of equal value
• This paper may not be retained by the candidate
• Answers must be written in ink, with the exception of graphs and multiple-choice an- swers sheets.
• No examination materials may be used.
• Electronic calculators provided by the University may be used.
• Provide answers to Question 1 in the space provided on the examination paper itself.
• Use a separate answer book for each of the other questions.
• Marks will be subtracted if the above rules are not followed.

SAMPLE COMP3231/COMP9201 Final Examination Question 1 [16 Marks]
Answer this question on the examination paper itself.
Classify each statement as true, by crossing the T box, or false, by crossing the F box. You will receive one mark for each correct classification, and lose one mark for each incorrect classification. You gain zero marks for each answer left unclassified. The overall mark for this question will not be negative, i.e. the minimum mark is zero.
T F T F T F T F T F T F T F T F T F T F
T F T F T F
A smaller page size leads to smaller page tables.
A smaller page size leads to more TLB misses.
A smaller page size leads to fewer page faults.
A smaller page size reduces paging I/O throughput.
Threads are cheaper to create than processes.
Kernel-implemented threads are cheaper to create than user-level-implemented threads. A blocking kernel-implemented thread blocks all threads in the process.
Threads are cheaper to context switch than processes.
A blocking user-level-implemented thread blocks the process.
Different user-level threads of the same process can have different scheduling priorities in the kernel.
All kernel-scheduled threads of a process share the same virtual address space. The optimal page replacement algorithm is the best choice in practice.
The operating system is not responsible for resource allocation between competing pro- cesses.
System calls do not change the privilege mode of the processor.
A scheduler favouring I/O-bound processes usually does not significantly delay the completion of CPU-bound processes.
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SAMPLE COMP3231/COMP9201 Final Examination Question 2 [12 Marks]
Answer this question in a separate book
A) [6 marks]
Consider a demand-paging system with a paging disk that has an average access and transfer time of 5 milliseconds for a single page. Addresses are translated through a page table in main memory, with an access time of 100 nanoseconds per memory access. Thus, each memory reference through the page table takes two accesses. The system has a 48-entry TLB to speed up memory accesses. Assume that 99% of memory accesses result in a TLB hit, and of the remaining 1%, 5 percent (or 0.05% of the total) cause page faults. What is the effective memory access time?
B) [6 marks]
Some versions of UNIX store the first part of each file in the same disk block as the inode. Discuss why this might be advantageous in practice.
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SAMPLE COMP3231/COMP9201 Final Examination Question 3 [14 Marks]
Answer this question in a separate book
A) [8 marks]
Suppose that the head of a moving-head disk with 192 tracks, numbered 0 to 191, is currently serving a request at track 80 and has just finished a request at track 62. The queue of requests is kept in the FIFO order: 119, 58, 114, 28, 111, 55, 103, 30, 75. What is the total number of tracks traversed by head movements needed to satisfy these requests for the following disk-scheduling algorithms?
i) FCFS. ii) SSTF.
iii) Elevator (SCAN).
iv) Modified Elevator (C-SCAN).
B) [6 marks]
User-level threads packages generally implement cooperative scheduling. What is cooperative scheduling, and why is it the common method used to schedule user-level threads?
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SAMPLE COMP3231/COMP9201 Final Examination
Question 4 [10 Marks]
Answer this question in a separate book
Explain how a 32-bit virtual address is translated into a physical address on a system using a two-level page table and 4kb pages. Your explanation, where it refers to parts of an address, must specifically state which bits of the address you are talking about. (Ignore any TLB). State any assumptions you make!
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SAMPLE COMP3231/COMP9201 Final Examination Question 5 [14 Marks]
Answer this question in a separate book
A) [6 marks]
Describe the difference between external and internal fragmentation. Indicate which of the two are
most likely to be an issues on a) a simple memory memory mangement machine using base limit registers and static partitioning, and b) a similar machine using dynamic partitioning.
B) [8 marks]
Describe the difference between a normal test-and-set spinlock and a read-before-test-and-set spin- lock. Why would the latter be advantageous over the former on multiprocessor systems.
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SAMPLE COMP3231/COMP9201 Final Examination
Question 6 [8 Marks]
Answer this question in a separate book
Describe the four conditions required for deadlock to occur. Describe a common method for deadlock prevention that prevents one of the conditions occurring.
Page 7 of 7

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