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    Interrupt driven I/O vs. polled I/O

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    In an 8-hour interval, an operator controls systems with 60 commands on the average, entered through a keyboard.
    a. Processor scans keyboard every 100 ms. Give check counts in an 8 hours period.
    b. If processor uses interrupt-driven I/O, how much does the processor save in fraction of its visits to the keyboard?

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    Solution Preview

    a. Processor scans keyboard every 100 ms.
    So in 1 second it will scan keyboard (1 second/100 ms) = (1000 ms/100 ms) = 10 times.
    Hence check counts in an 8 hours period = 8 hrs * 3600 seconds/hr * 10 times/second = 288,000 times

    b. As ...

    Solution Summary

    Since nothing is specified about the size of operator commands in the question, solution assumes that either these are single character commands issued at different points in time, or we have an intelligent keyboard that interrrupts processor only when operator has typed in the complete command.