What is C-scan disk scheduling:-
In SCAN algorithm, the disk arm again scans the path that has been scanned, after reversing its direction. So, it may be possible that too many requests are waiting at the other end or there may be zero or few requests pending at the scanned area. These situations are avoided in CSAN algorithm in which the disk arm instead of reversing its direction goes to the other end of the disk and starts servicing the requests from there. So, the disk arm moves in a circular fashion and this algorithm is also similar to SCAN algorithm and hence it is known as C-SCAN (Circular SCAN).
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. head movement is towards low values.
Advantage:-
- Uniform waiting time
- Better response time
Disadvantage:-
- In C-SCAN even if there are no requests left to be serviced the Head will still travel to the end of the disk unlike SCAN algorithm.
Code:-
#include<stdio.h>
#include<stdlib.h>
int main()
{
int RQ[100],i,j,n,TotalHeadMoment=0,initial,size,move;
printf("Enter the number of Requests\n");
scanf("%d",&n);
printf("Enter the Requests sequence\n");
for(i=0;i<n;i++)
scanf("%d",&RQ[i]);
printf("Enter initial head position\n");
scanf("%d",&initial);
printf("Enter total disk size\n");
scanf("%d",&size);
printf("Enter the head movement direction for high 1 and for low 0\n");
scanf("%d",&move);
// logic for C-Scan disk scheduling
/*logic for sort the request array */
for(i=0;i<n;i++)
{
for( j=0;j<n-i-1;j++)
{
if(RQ[j]>RQ[j+1])
{
int temp;
temp=RQ[j];
RQ[j]=RQ[j+1];
RQ[j+1]=temp;
}
}
}
int index;
for(i=0;i<n;i++)
{
if(initial<RQ[i])
{
index=i;
break;
}
}
// if movement is towards high value
if(move==1)
{
for(i=index;i<n;i++)
{
TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
initial=RQ[i];
}
// last movement for max size
TotalHeadMoment=TotalHeadMoment+abs(size-RQ[i-1]-1);
/*movement max to min disk */
TotalHeadMoment=TotalHeadMoment+abs(size-1-0);
initial=0;
for( i=0;i<index;i++)
{
TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
initial=RQ[i];
}
}
// if movement is towards low value
else
{
for(i=index-1;i>=0;i--)
{
TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
initial=RQ[i];
}
// last movement for min size
TotalHeadMoment=TotalHeadMoment+abs(RQ[i+1]-0);
/*movement min to max disk */
TotalHeadMoment=TotalHeadMoment+abs(size-1-0);
initial =size-1;
for(i=n-1;i>=index;i--)
{
TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
initial=RQ[i];
}
}
printf("Total head movement is %d",TotalHeadMoment);
return 0;
}
#include <iostream>
#include <cstdlib>
using namespace std;
int main() {
int RQ[100], i, j, n, TotalHeadMoment = 0, initial, size, move;
cout << "Enter the number of Requests" << endl;
cin >> n;
cout << "Enter the Requests sequence" << endl;
for (i = 0; i < n; i++)
cin >> RQ[i];
cout << "Enter initial head position" << endl;
cin >> initial;
cout << "Enter total disk size" << endl;
cin >> size;
cout << "Enter the head movement direction for high 1 and for low 0" << endl;
cin >> move;
// Logic for C-Scan disk scheduling
// Logic for sorting the request array
for (i = 0; i < n; i++) {
for (j = 0; j < n - i - 1; j++) {
if (RQ[j] > RQ[j + 1]) {
int temp;
temp = RQ[j];
RQ[j] = RQ[j + 1];
RQ[j + 1] = temp;
}
}
}
int index;
for (i = 0; i < n; i++) {
if (initial < RQ[i]) {
index = i;
break;
}
}
// If movement is towards high value
if (move == 1) {
for (i = index; i < n; i++) {
TotalHeadMoment = TotalHeadMoment + abs(RQ[i] - initial);
initial = RQ[i];
}
// Last movement for max size
TotalHeadMoment = TotalHeadMoment + abs(size - RQ[i - 1] - 1);
// Movement max to min disk
TotalHeadMoment = TotalHeadMoment + abs(size - 1 - 0);
initial = 0;
for (i = 0; i < index; i++) {
TotalHeadMoment = TotalHeadMoment + abs(RQ[i] - initial);
initial = RQ[i];
}
}
// If movement is towards low value
else {
for (i = index - 1; i >= 0; i--) {
TotalHeadMoment = TotalHeadMoment + abs(RQ[i] - initial);
initial = RQ[i];
}
// Last movement for min size
TotalHeadMoment = TotalHeadMoment + abs(RQ[i + 1] - 0);
// Movement min to max disk
TotalHeadMoment = TotalHeadMoment + abs(size - 1 - 0);
initial = size - 1;
for (i = n - 1; i >= index; i--) {
TotalHeadMoment = TotalHeadMoment + abs(RQ[i] - initial);
initial = RQ[i];
}
}
cout << "Total head movement is " << TotalHeadMoment << endl;
return 0;
}
def main():
RQ = []
TotalHeadMoment = 0
n = int(input("Enter the number of Requests\n"))
print("Enter the Requests sequence")
for _ in range(n):
RQ.append(int(input()))
initial = int(input("Enter initial head position\n"))
size = int(input("Enter total disk size\n"))
move = int(input("Enter the head movement direction for high 1 and for low 0\n"))
# Logic for C-Scan disk scheduling
# Logic for sorting the request array
RQ.sort()
index = 0
for i in range(n):
if initial < RQ[i]:
index = i
break
# If movement is towards high value
if move == 1:
for i in range(index, n):
TotalHeadMoment += abs(RQ[i] - initial)
initial = RQ[i]
# Last movement for max size
TotalHeadMoment += abs(size - RQ[i - 1] - 1)
# Movement max to min disk
TotalHeadMoment += abs(size - 1 - 0)
initial = 0
for i in range(index):
TotalHeadMoment += abs(RQ[i] - initial)
initial = RQ[i]
# If movement is towards low value
else:
for i in range(index - 1, -1, -1):
TotalHeadMoment += abs(RQ[i] - initial)
initial = RQ[i]
# Last movement for min size
TotalHeadMoment += abs(RQ[i + 1] - 0)
# Movement min to max disk
TotalHeadMoment += abs(size - 1 - 0)
initial = size - 1
for i in range(n - 1, index - 1, -1):
TotalHeadMoment += abs(RQ[i] - initial)
initial = RQ[i]
print(f"Total head movement is {TotalHeadMoment}")
if __name__ == "__main__":
main()
Text Copied!
Output:-
Enter the number of Request
8
Enter the Requests Sequence
95 180 34 119 11 123 62 64
Enter initial head position
50
Enter total disk size
200
Enter the head movement direction for high 1 and for low 0
1
Total head movement is 382
Program of disk scheduling algorithm
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