A system that is available 90% of the time is said to have one ‘‘9’’ of availability. Of the 365 days in a year, such a system would be ‘‘down’’ about 36 days and 12 hours.

i. A system that is available 99% of the time has two ‘‘9’s’’. How many days and hours per year is this system ‘‘down’’?

ii. How many days, hours, and minutes is a system with three ‘‘9’s’’ of availability down?

iii. How many hours, minutes, and seconds is a system with four ‘‘9’s’’ of availability down?

iv. How many minutes and seconds is a system with five ‘‘9’s’’ of availability down?

v. How many minutes and seconds is a system with six ‘‘9’s’’ of availability down?

vi. Where does the general class of personal computers fall in this spectrum of availability? Where do you think the air control system of the Federal Aviation Administration for a country should fall in this spectrum? Where does the telephone system fall? Where does your Internet provider fall?