GATE CS 2023 Set 1 — Question 34
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Question
A keyboard connected to a computer is used at a rate of 1 keystroke per second. The computer system polls the keyboard every 10 ms (milli seconds) to check for a keystroke and consumes 100 s (micro seconds) for each poll. If it is determined after polling that a key has been pressed, the system consumes an additional 200 s to process the keystroke. Let denote the fraction of a second spent in polling and processing a keystroke.In an alternative implementation, the system uses interrupts instead of polling. An interrupt is raised for every keystroke. It takes a total of 1 ms for servicing an interrupt and processing a keystroke. Let denote the fraction of a second spent in servicing the interrupt and processing a keystroke.The ratio is ________. (Rounded off to one decimal place)
Correct answer
10.2 to 10.2
Solution
Step 1: Calculate the total time spent in polling per second.
Polling interval = 10 ms, so there are polls per second.
Time for each poll = 100 s.
Total polling time = .Step 2: Calculate the time spent processing keystrokes in the polling method.
Keystroke rate = 1 per second.
Processing time per keystroke = 200 s.
Total processing time = .Step 3: Calculate (fraction of a second).
.Step 4: Calculate for the interrupt method.
Interrupt servicing and processing time = 1 ms = 1,000 s.
Since there is 1 keystroke per second, total time spent = 1,000 s.
.Step 5: Calculate the ratio.
Ratio .
Polling interval = 10 ms, so there are polls per second.
Time for each poll = 100 s.
Total polling time = .Step 2: Calculate the time spent processing keystrokes in the polling method.
Keystroke rate = 1 per second.
Processing time per keystroke = 200 s.
Total processing time = .Step 3: Calculate (fraction of a second).
.Step 4: Calculate for the interrupt method.
Interrupt servicing and processing time = 1 ms = 1,000 s.
Since there is 1 keystroke per second, total time spent = 1,000 s.
.Step 5: Calculate the ratio.
Ratio .
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