Operating Systems Assignment 12 ● No programming for this assignment. [100 points] Problem Set 1. [20 points] (from Chapter 12) Explain why SSTF scheduling tends to favor middle cylinders over the innermost and outermost cylinders. 2. [20 points] 12.8 Requests are not usually uniformly distributed. For example, we can expect a cylinder containing the file-system metadata to be accessed more frequently than a cylinder containing only files. Suppose you know that 50 percent of the requests are for a small, fixed number of cylinders. a. Would any of the scheduling algorithms discussed in this chapter be particularly good for this case? Explain your answer. b. Propose a disk-scheduling algorithm that gives even better performance by taking advantage of this “hot spot” on the disk. 3. [40 points] 13.3 Consider the following I/O scenarios on a single-user PC: a. A mouse used with a graphical user interface b. A tape drive on a multitasking operating system (with no device preallocation available) c. A disk drive containing user files d. A graphics card with direct bus connection, accessible through memory-mapped I/O For each of these scenarios, would you design the operating system to use buffering, spooling, caching, or a combination? Would you use polled I/O or interrupt-driven I/O? Give reasons for your choices. 4. [20 points] 13.7 Typically, at the completion of a device I/O, a single interrupt is raised and appropriately handled by the host processor. In certain settings, however,the code that is to be executed at the completion of the I/O can be broken into two separate pieces. The first piece executes immediately after the I/O completes and schedules a second interrupt for the remaining piece of code to be executed at a later time. What is the purpose of using this strategy in the design of interrupt handlers?
