Homework Assignment #3 J. H. Wang Dec. 5, 2007

Homework #3 Chap.8: 8.1, 8.5 Chap.9: 9.4, 9.12 Chap.12: 12.11 Due: two weeks (Dec. 19, 2007)

Chap.8 8.1: Explain the difference between internal and external fragmentation. 8.5: Compare paging with segmentation with respect to the amount of memory required by the address translation structures in order to convert virtual addresses to physical addresses.

Chap.9 9.4: Assume that we have a demand-paged memory. The page table is held in registers. It takes 8 milliseconds to service a page fault if an empty frame is available or if the replaced page is not modified and 20 milliseconds if the replaced page is modified. Memory-access time is 100 nanoseconds. Assume that the page to be replaced is modified 70 percent of the time. What is the maximum acceptable page-fault rate for an effective access time of no more than 200 nanoseconds?

9.12: Consider the parameter  used to define the working-set window in the working-set model. What is the effect of setting  to a small value on the page fault frequency and the number of active (non-suspended) processes currently executing in the system? What is the effect when  is set to a very large value?

Chap.12 12.11: The reliability of a hard-disk drive is typically described in terms of a quantity called mean time between failures (MTBF). Although this quantity is called a “time,” the MTBF actually is measured in drive-hours per failure. (a) If a system contains 1,000 disk drives, each of which has a 750,000-hour MTBF, which of the following best describes how often a drive failure will occur in that disk farm: once per thousand years, once per century, once per decade, once per year, once per month, once per week, once per day, once per hour, once per minute, or once per second?

(b) Mortality statistics indicate that, on the average, a U. S (b) Mortality statistics indicate that, on the average, a U.S. resident has about 1 in 1,000 chance of dying between ages 20 and 21 years. Deduce the MTBF hours for 20-year-olds. Convert this figure from hours to years. What does this MTBF tell you about the expected lifetime of a 20-year-old? (c) The manufacturer guarantees a 1-million-hour MTBF for a certain model of hard drive. What can you conclude about the number of years for which one of these drives is under warranty?