308
Operating CprE Systems: Principles and Practice
Exam 2
May 3, 2005, 7.30-9.30am
Name: Section:
Note
The maximum score on this exam is 100 points. The maximum time allowed is 2 hours. This is a closed book exam.
Problem 1
1 pt Are le names in UNIX case sensitive?
2 pts Which UNIX system call creates a new address space?
3 pts What is the problem if physical (not virtual) memory addresses are generated at compile time?
3 pts In a virtual memory system with a 32 bit virtual address space and 128MB physical memory: (a) How large is the virtual address space?
(b) What is the maximum amount of memory you can expect your programs to consume without the system thrashing?
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
3 pts Consider a le system that uses a buer cache. If power outages are frequent, then which strategy would you recommend for handling writes to les? Explain.
4 pts Suppose you want to share a le with three friends and give them read and write access to the le (and access to no one else). Explain how you would accomplish this on a UNIX le system.
3 pts List the steps taken by the operating system in response to a page fault.
4 pts One way to keep track of the disk blocks associated with a le is through contiguous allocation, where each le is stored as a contiguous run of disk blocks. Name one advantage and one disadvantage of this scheme.
2
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
4 pts Is it feasible to use a 1-level page table for a 40-bit address space? Explain. Assume that each page table entry takes 4 bytes and the page size is 4KB.
5 pts Name ve system calls provided by the UNIX le system.
3 pts What is the advantage of programming in a language that uses garbage collection?
3
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
Problem 2
5 pts Consider a 20 GB disk organized using a FAT le system. Assume that the block size is 10KB, and that each entry of the FAT takes 4 bytes. How large is the FAT?
5 pts Consider the UNIX i-node organization whose disk map contains 13 pointers to disk blocks: 10 direct, 1 indirect, 1 double indirect and 1 triple indirect. Assume that each disk block is 4KB (4096 bytes), and that a pointer to a disk block takes 4 bytes. How many disk operations are required to read the 100,000th byte in a le? Explain your answer. Assume that the i-node of the le is in memory.
4
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
4 pts In a UNIX le system, list all disk accesses needed for examining the contents of the le /usr/snt/../snt/data.txt. Assume that at the beginning, the root inode and the root directory are already in memory, but no other directories or inodes are in memory. Also assume that the le data.txt ts in one disk block. Explain your answer.
5
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
Problem 3
10 pts Page Replacement Algorithms Consider the following page-reference string from a process 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5 For each page reference, specify whether a page fault occurs or not with the LRU algorithm and the Optimal algorithm. Assume that the system has three page frames. Also assume that all the frames are initially empty, so that the rst reference to a page will always cost a fault. Under every page reference, mark whether there was a page-fault or not, and write the contents of the frames page at the end of the reference (i.e. after the instruction has been executed). (a) LRU (Least Recently Used) Page Accessed Mark if page fault occurs Contents of Page frame 1 Contents of Page frame 2 Contents of Page frame 3 Initial Nil Nil Nil 1 2 1 2 3 1 2 3 4 1 2 3 4 5
(b) For the optimal algorithm (which has knowledge of future requests), show the page fault sequence as in the previous question. Page Accessed Mark if page fault occurs Contents of Page frame 1 Contents of Page frame 2 Contents of Page frame 3 4 pts Implementation Which of the above algorithms (LRU and Optimal) can be implemented exactly in a real operating system? Explain your answer. Initial Nil Nil Nil 1 2 1 2 3 1 2 3 4 1 2 3 4 5
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CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
Problem 4
6 points Consider a virtual memory system which uses single level page tables for the address translation, and which has the following observed parameters. TLB hit ratio = 90% Physical memory latency = 100 nanoseconds Penalty of a page fault = 10 milliseconds Suppose page faults occur every X instructions. What is the minimum value of X so that the average memory latency is less than 120 nanoseconds? Assume that the lookup time in the TLB is negligible, and that the whole page table can be stored in physical memory. Show your intermediate steps so that we can give you partial credit, if needed.
7
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
10 points Consider a demand-paging system with the following parameters. CPU Utilization = 20% Disk Utilization due to Paging = 99% Other I/O devices = 5% For each of the following, briey explain whether it is likely to improve the CPU utilization. (a) Install a faster CPU (b) Install a bigger disk for paging (c) Decrease the degree of multiprogramming (d) Install more main memory (e) Install a faster disk for paging
8
CprE 308
Exam 2
May 3, 2005, 7.30-9.30am
Problem 5
3 points A real-time system has two periodic events with periods of 20, 40 m...