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CS439: Principles of Computer Systems

Homework 8, Part 1

Due: 8:45a Friday, March 28, 2014

Part 1 of the homeworks must be submitted electronically. Please refer to the homework turnin instructions.

  1. The MegaGiga hard disk rotates at 5400 rpm with an arm seek time given by = 4 + 0.05t msec, where t is the number of tracks the arm seeks. Assume a block size of 512 bytes, and 1024 tracks with 512 blocks/track. The disk controller and DMA read or write data from/to disk at a rate of 4MB/sec. What is the storage capacity of the disk?
  2. Disk requests come into the disk driver for tracks 10, 22, 20, 2, 40, 6, and 38, in that order. A seek takes 6 msec per track moved. How much seek time is needed for the following scheduling algorithms?
    a) FIFO
    b) SSTF
    c) LOOK (SCAN, but doesn't move to the end)
    In all cases, the arm is initially at track 20, and you may assume that the head is traveling towards higher numbers.

    Adapted from Tannenbaum Chapter 5 Number 24.

  3. Some file allocation schemes limit the size of the file whether or not there is enough space for a larger file. Which ones and why?
    1. Linked
    2. Direct
    3. Contiguous
    4. Multi-Level index
    5. Extents
  4. Which file allocation scheme that we studied is most similar to paging? segmentation?
  5. Pooh Software Ltd. is selling a file system that uses a UNIX-like file system with multi-level indexing. For more reliability, the inode array is actually replicated on the disk in two different places. The intent is that if one or a group of sectors that are storing either replica of the array become bad, the system can always recover from the replica. Discuss the effect of having this replicated data structure on performance.