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GATE 2025 CS (CS1) – Question 29

Operating System · CPU and I/O Scheduling · 1 mark · Numerical answer

Suppose in a multiprogramming environment, the following C program segment is executed. A process goes into I/O queue whenever an I/O related operation is performed. Assume that there will always be a context switch whenever a process requests for an I/O, and also whenever the process returns from an I/O. The number of times the process will enter the ready queue during its lifetime (not counting the time the process enters the ready queue when it is run initially) is _______. (Answer in integer)

int main()
{
    int x=0,i=0;
    scanf("%d",&x);
    for(i=0; i<20; i++)
    {
        x = x+20;
        printf("%d\n",x);
    }
    return 0;
}

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Show answer and explanation

Correct answer: 21

Explanation

Each I/O operation sends the process to the I/O queue, and on completion it re-enters the ready queue. There is 1 scanf and 20 printf calls, so 21 re-entries.