The reliability of a hard-disk drive is typically described in terms ofa quantity called

Chapter 10, Problem 10.21

(choose chapter or problem)

The reliability of a hard-disk drive is typically described in terms ofa quantity called mean time between failures (MTBF). Although thisquantity is called a time, the MTBF actually is measured in drive-hoursper 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 adrive 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, oronce per second?b. Mortality statistics indicate that, on the average, a U.S. residenthas about 1 chance in 1,000 of dying between the ages of 20 and 21.Deduce the MTBF hours for 20-year-olds. Convert this figure fromhours to years. What does this MTBF tell you about the expectedlifetime of a 20-year-old? c. The manufacturer guarantees a 1-million-hour MTBF for a certainmodel of disk drive. What can you conclude about the number ofyears for which one of these drives is under warranty?