GATE CS 2015 Set 1 — Question 56
Go beyond PYQs with Success TrackerAI-powered personalised practice and doubt support. Unlimited practice on eligible plans; AI usage limits apply.NAT+2 / -0MediumDisk Scheduling AlgorithmsI/O OrganizationComputer Organization & Architecture
Computer Organization & Architecture → I/O Organization → Disk Scheduling Algorithms
Last updated
Question
Suppose the following disk request sequence (track numbers) for a disk with 100 tracks is given: 45, 20, 90, 10, 50, 60, 80, 25, 70. Assume that the initial position of the R/W head is on track 50. The additional distance that will be traversed by the R/W head when the Shortest Seek Time First (SSTF) algorithm is used compared to the SCAN (Elevator) algorithm (assuming that SCAN algorithm moves towards 100 when it starts execution) is_________ tracks.
Correct answer
10 to 10
Solution
SSTF (Shortest Seek Time First):
Initial position: 50
Requests: {10, 20, 25, 45, 50, 60, 70, 80, 90}
(Note: 50 is in the request list and is serviced immediately at start)Sequence:
Total Distance =
tracks.SCAN (Elevator):
Initial position: 50, Direction: Towards 100 (Up)
Requests in Up direction: 50, 60, 70, 80, 90
Requests in Down direction: 45, 25, 20, 10Path (assuming LOOK behavior as is common in such problems unless 'end' is specified as a target):
tracks.
Initial position: 50
Requests: {10, 20, 25, 45, 50, 60, 70, 80, 90}
(Note: 50 is in the request list and is serviced immediately at start)Sequence:
1.Start at 50. Closest is 45 (dist 5).
2.At 45. Closest is 60 (dist 15) vs 25 (dist 20). Go to 60.
3.At 60. Closest is 70 (dist 10).
4.At 70. Closest is 80 (dist 10).
5.At 80. Closest is 90 (dist 10).
6.At 90. Closest is 25 (dist 65).
7.At 25. Closest is 20 (dist 5).
8.At 20. Closest is 10 (dist 10).
Path: Total Distance =
tracks.SCAN (Elevator):
Initial position: 50, Direction: Towards 100 (Up)
Requests in Up direction: 50, 60, 70, 80, 90
Requests in Down direction: 45, 25, 20, 10Path (assuming LOOK behavior as is common in such problems unless 'end' is specified as a target):
1.Move Up:
2.Reverse at 90 (last request in this direction).
3.Move Down:
Total Distance = tracks.Difference:tracks.
Continue learning with Success Tracker
A step still unclear? Work through it with support
Use Success Tracker to ask about the reasoning, then try another GATE CS question to check your understanding.
AI-powered practice· Unlimited practice on eligible plans
- PYQs with solutions
- Attempt available previous-year questions, then compare your reasoning with the worked solution. Coverage varies by stream.
- Practice that adapts
- Choose a topic, work on weaker areas and bookmark questions to revisit. Your attempts feed your progress tracking.
- AI doubt support
- Ask follow-up questions about a step or concept while practising, instead of stopping at the final answer.
Unlimited practice is available on eligible plans. Free practice and AI usage have limits; check the current plan allowances before choosing.
This page stays readable without an account. AI responses can be wrong; check them against the solution and source material.
More questions on I/O Organization
2026 Set 1 Q14Match each addressing mode in List I with a data element or an element of a data structure (in…2026 Set 1 Q15Consider a processor P whose instruction set architecture is the load-store architecture. The…2026 Set 1 Q16Which one of the following dependencies among the register operands of different instructions can…2026 Set 2 Q18Consider the following two statements about interrupt handling mechanisms in a CPU. S1: In…2026 Set 1 Q38The size of the physical address space of a processor is bytes. The capacity of a cache…