29 votes 29 votes Which of the following disk scheduling strategies is likely to give the best throughput? Farthest cylinder next Nearest cylinder next First come first served Elevator algorithm Operating System gate1999 operating-system disk-scheduling normal + – Kathleen asked Sep 23, 2014 • edited Feb 22, 2018 by go_editor Kathleen 11.4k views answer comment Share Follow See all 4 Comments See all 4 4 Comments reply Hira Thakur commented Jan 9, 2017 reply Follow Share what is Farthest cylinder next algorithm 1 votes 1 votes Chhotu commented Dec 18, 2017 reply Follow Share Option (B) and (D) both are acceptable. For more details please check comment of @Vicky rix ji. 1 votes 1 votes tusharp commented Mar 19, 2018 i edited by tusharp Apr 20, 2019 reply Follow Share As throughput is asked can it be interpreted as at any point of time during disk scheduling which Algo gives max request processing per second. Which implies minimum head movements. 0 votes 0 votes rfzahid commented Jan 17, 2019 reply Follow Share @tusharp It should be minimum head movements not maximum as overall seek latency is minimum when head movements are minimum thus maximum throughput. 0 votes 0 votes Please log in or register to add a comment.
Best answer 42 votes 42 votes Farthest cylinder next $\rightarrow$ This might be candidate for worst algorithm . This is false. Nearest cylinder next $\rightarrow$ This is output. First come first served $\rightarrow$ This will not give best throughput. It is random . Elevator algorithm $\rightarrow$ This is good but issue is that once direction is fixed we don't come back, until we go all the other way. So it does not give best throughput. Correct Answer: $B$ Akash Kanase answered Nov 26, 2015 • edited May 21, 2019 by Naveen Kumar 3 Akash Kanase comment Share Follow See all 14 Comments See all 14 14 Comments reply sushmita commented Sep 25, 2016 reply Follow Share I am confused between nearest cylinder next or elevator?? Because both gives good throughput. what should be the answer?? and why?? why it shouldnt be elevator since it doesnt even have starvation problem?? 9 votes 9 votes vaishali jhalani commented Dec 17, 2016 reply Follow Share How to decide between nearest cylinder and elevator algo. 2 votes 2 votes Puja Mishra commented Feb 5, 2017 reply Follow Share Option B is like SSTF ... 2 votes 2 votes Chhotu commented Dec 1, 2017 reply Follow Share Hi @sushmita, vaishali jhalani and Puja Mishra ji, First of all thanks for raising good point. But could you please provide some counter example where Elevator algorithm will perform better then Nearest cylinder next ? 0 votes 0 votes Gate Ranker18 commented Dec 2, 2017 reply Follow Share In nearest cylinder next, we cant fix the direction in which go next but in Elevator , first we fix the diection then go only that direction and then come back to opposite direction like if we have 10,50 request and head is on 20 then nearest cylinder next , 20->10->50 total seek time 10+40=50 elevator 20->50->10 total seek time=30+40=70 ( direction is fix toward 50) 5 votes 5 votes Vicky rix commented Dec 11, 2017 i edited by Vicky rix Dec 11, 2017 reply Follow Share As long as the block request string is given, we cannot decide between B) and D) B) is not always the best EX: 19 votes 19 votes Venkat Sai commented Dec 18, 2017 reply Follow Share throughput put depends on the number of requests served per second as we always go for the shortest reach SSTF Does this best as it tries to serve the maximum number of processes in less time @https://gateoverflow.in/user/sushmita 5 votes 5 votes Chhotu commented Dec 18, 2017 reply Follow Share Thank you @Vicky rix ji. 2 votes 2 votes Puja Mishra commented Dec 19, 2017 reply Follow Share Scan is called elevator algorithm ... 4 votes 4 votes Brij Mohan Gupta commented Jul 27, 2018 reply Follow Share For more reference go to this question. https://gateoverflow.in/8227/gate2015-1-30 How SCAN Algo hear move one side head and then return. 0 votes 0 votes Ayush Upadhyaya commented Sep 29, 2018 reply Follow Share It should be Elevator algorithm since it provides more uniform waiting time than the SSTF or nearest cylinder next algorithm. 5 votes 5 votes Chirag Shilwant commented Dec 20, 2019 reply Follow Share Both B AND D are correct. D is also correct(see @Vicky rix comment ) and as it's a GATE 1999 question multiple options are possible as answers. 2 votes 2 votes Abhineet Singh commented Dec 8, 2020 reply Follow Share I dont think there can be 2 correct answers for this as it is asking for the BEST, how can two strategies be best simultaneously. What to write if it appears in the exam now…. Other sites like GFG have also given B 0 votes 0 votes rupesh17 commented Jan 19, 2021 reply Follow Share Abhineet Singh see question is asking- likely to give the best throughput hence Nearest cylinder next is better option for exam 2 votes 2 votes Please log in or register to add a comment.
12 votes 12 votes Option B Nearest cylinder next but it can lead to starvation Bhagirathi answered Jul 4, 2015 Bhagirathi comment Share Follow See all 0 reply Please log in or register to add a comment.
11 votes 11 votes Nearest cylinder next . in this many pages can be accessed in less time . So throughput will be high . set2018 answered Sep 1, 2017 set2018 comment Share Follow See all 0 reply Please log in or register to add a comment.
5 votes 5 votes The only catch in the question is that they are asking for the most likely to give the best throughput. Even if for some cases SCAN can have better results but the most likely to result the best throughput is Nearest cylinder Algo ;) Gru answered Jul 21, 2018 Gru comment Share Follow See all 0 reply Please log in or register to add a comment.