Python-Program of SSTF (Short seek time first )Disk scheduling Algorithms in operating system (OS).

   What is SSTF disk scheduling:-

                                                        Shortest seek time first (SSTF) algorithm selects the disk I/O request which requires the least disk arm movement from its current position regardless of the direction. It reduces the total seek time as compared to FCFS.

Example:-: Given the following queue -- 95, 180, 34, 119, 11, 123, 62, 64 with the Read-write head initially at the track 50 and the tail track being at 199.

Advantage:-

1. seek time reduces as compared to the FCFS
2. Less waiting time and response time 
3. Increase throughput.

Disadvantage:-

1. starvation occurred

  Python     C      C++  

import sys

n = int(input("Enter the number of Requests\n"))

RQ =list(map(int,input().split()))

print("Enter the Requests sequence")

initial = int(input("Enter initial head position\n"))

# logic for sstf disk scheduling

count = 0

TotalHeadMoment = 0

# loop will execute until all processes are completed

while count != n:

    mini = sys.maxsize

    d = index = 0

    for i in range(n):

        d = abs(RQ[i] - initial)

        if mini > d:

            mini = d

            index = i

    TotalHeadMoment += mini

    initial = RQ[index]

    RQ[index] = sys.maxsize

    count += 1

print("Total head movement is", TotalHeadMoment)

Output:-

Enter the number of Request

8

Enter Request Sequence

95 180 34 119 11 123 62 64

Enter initial head Position

50

Total head movement is 236

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•   Program of disk scheduling algorithm

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