12-exr - 12 C H A P T E R Mass Storage Structure Practice...

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Unformatted text preview: 12 C H A P T E R Mass Storage Structure Practice Exercises 12.1 The accelerating seek described in Exercise 12.3 is typical of hard-disk drives. By contrast, floppy disks (and many hard disks manufactured before the mid-1980s) typically seek at a fixed rate. Suppose that the disk in Exercise 12.3 has a constant-rate seek rather than a constant- acceleration seek, so the seek time is of the form t = x + yL , where t is the time in milliseconds and L is the seek distance. Suppose that the time to seek to an adjacent cylinder is 1 millisecond, as before, and is 0.5 milliseconds for each additional cylinder. a. Write an equation for this seek time as a function of the seek distance. b. Using the seek-time function from part a, calculate the total seek time for each of the schedules in Exercise 12.2. Is your answer the same as it was for Exercise 12.3(c)? c. What is the percentage speedup of the fastest schedule over FCFS in this case? 12.2 Is disk scheduling, other than FCFS scheduling, useful in a single-user environment? Explain your answer. 12.3 Explain why SSTF scheduling tends to favor middle cylinders over the innermost and outermost cylinders. 12.4 Why is rotational latency usually not considered in disk scheduling? How would you modify SSTF, SCAN, and C-SCAN to include latency optimization? 12.5 How would use of a RAM disk affect your selection of a disk-scheduling algorithm? What factors would you need to consider? Do the same considerations apply to hard-disk scheduling, given that the file system stores recently used blocks in a buffer cache in main memory? 25 26 Chapter 12 Mass-Storage Structure 12.6 Why is it important to balance file system I/O among the disks and controllers on a system in a multitasking environment? 12.7 What are the tradeoffs involved in rereading code pages from the file system versus using swap space to store them?...
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This note was uploaded on 11/03/2009 for the course IT OS taught by Professor Dr.stephan during the Winter '09 term at Abu Dhabi University.

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12-exr - 12 C H A P T E R Mass Storage Structure Practice...

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