4,898 views
2 votes
2 votes

There are 200 tracks on a disc platter and the pending requests have come in the order - 36, 69, 167, 76, 42, 51, 126, 12 and 199. Assume the arm is located at the 100th track and moving towards track 200. If sequence of disc access is 126, 167, 199, 12, 36, 42, 51, 69 and 76 then which disc access scheduling policy is used?

  1. Elevator
  2. Shortest seek-time first
  3. C-SCAN
  4. First Come First Served

5 Answers

Best answer
3 votes
3 votes
It should be C-SCAN il  as the disc access has continued towards the nearest end from initial from 100 and

serviced126,167,199  untill it has hit end the top max

and then jumped to the other end and serviced 12,36,42,51,69,76 in similar manner .
3 votes
3 votes

answer is (c). C-SCAN because it has been started from 100th and serving all the right hand side request till the last point then reverse the direction and starts from track 0 to serve further request.

SCAN will just reverse direction and service the next closest disk request and C-SCAN will always go back to track 0 and start going to higher track requests on reversal.

for more info@

http://www.cs.iit.edu/~cs561/cs450/disksched/disksched.html

1 votes
1 votes
After 199 it is moving to 12 . so it should be elevator algo.and in circular scan it will move upto 0
1 votes
1 votes
Answer is C-SCAN.

SCAN is wrong because it works like elevator servicing requests while going up and coming down, whereas in this case if you observe series [126, 167, 199, 12, 36, 42, 51, 69 and 76 ], after 199 it suppose to scan 76 but not 12.

If SCAN then answer would be in the series-126,167,199,76,69,51,42,36,12]

So in C-SCAN starts from 100, 126,167, and after reaching 199, without servicing any request during return it will reach 0 initially, then it start servicing requests on the way from 0 [12,36,42,51,69 and 76].till it reaches end of the disk.
Answer:

Related questions

8 votes
8 votes
3 answers
1
go_editor asked Jul 1, 2016
4,647 views
Which of the following is not an optimization criterion in the design of a CPU scheduling algorithm?Minimum CPU utilizationMaximum throughputMinimum turnaround timeMinimu...
4 votes
4 votes
4 answers
2
go_editor asked Jul 1, 2016
5,597 views
Dirty bit is used to indicate which of the following?A page fault has occurredA page has corrupted dataA page has been modified after being loaded into cacheAn illegal ac...
9 votes
9 votes
3 answers
3
go_editor asked Jul 1, 2016
6,476 views
What is the minimum number of resources required to ensure that deadlock will never occur, if there are currently three processes $P_1, P_2$ and $P_3$ running in a system...
4 votes
4 votes
3 answers
4