###### Question 5070 – Operating-Systems
November 17, 2023
###### Question 5215 – Operating-Systems
November 17, 2023
###### Question 5070 – Operating-Systems
November 17, 2023
###### Question 5215 – Operating-Systems
November 17, 2023

style=”font-weight: 400;”>Consider the input/output (I/O) requests made at different instants of time directed at a hypothetical disk having 200 tracks as given in the following table :

style=”font-weight: 400;”>Assume that :

style=”font-weight: 400;”>Current head position is at track no. 65

style=”font-weight: 400;”>Direction of last movement is towards higher numbered tracks

style=”font-weight: 400;”>Current clock time is 160 milliseconds

style=”font-weight: 400;”>Head movement time per track is

style=”font-weight: 400;”>1 millisecond.

style=”font-weight: 400;”>“look” is a variant of “SCAN” disk arm scheduling algorithm. In this algorithm, if no more I/O requests are left in current direction, the disk head reverses its direction. The seek times in Shortest Seek First (SSF) and “look” disk-arm scheduling algorithms respectively are

Correct Answer: B

Question 625 Explanation:
Given data
Current head position is at track no. 65
The direction of last movement is towards higher numbered tracks
Current clock time is 160 milliseconds
Head movement time per track is 1 millisecond.

According to clock time, the serial no 1,2,3 and 4 tracks are ready to process.
SSTF( Shortest Seek time First )
Current head position is 65, according to SSTF next track is 75 but it will arrive at the time of 175, then it will process 85 first, then track 75 later 100 from there it will process 40 and then 12
so the requests are 65 → 85→ 75→ 100→ 40→ 12
= (85-65)+(85-75)+(100-75)+(100-40)+(40-12)
= 20+10+25+60+28
= 143 ms
Look method:
The requests are processed in the following way
Direction of last movement is towards higher number of tracks.
65→ 85→ 100→ 75→ 40→ 12
=(85-65)+(100-85)+(100-75)+(75-40)+(40-12)
=20+15+25+35+28
=123ms
Given data
Current head position is at track no. 65
The direction of last movement is towards higher numbered tracks
Current clock time is 160 milliseconds
Head movement time per track is 1 millisecond.

According to clock time, the serial no 1,2,3 and 4 tracks are ready to process.
SSTF( Shortest Seek time First )
Current head position is 65, according to SSTF next track is 75 but it will arrive at the time of 175, then it will process 85 first, then track 75 later 100 from there it will process 40 and then 12
so the requests are 65 → 85→ 75→ 100→ 40→ 12
= (85-65)+(85-75)+(100-75)+(100-40)+(40-12)
= 20+10+25+60+28
= 143 ms
Look method:
The requests are processed in the following way
Direction of last movement is towards higher number of tracks.
65→ 85→ 100→ 75→ 40→ 12
=(85-65)+(100-85)+(100-75)+(75-40)+(40-12)
=20+15+25+35+28
=123ms

144 and 123 milliseconds
143 and 123 milliseconds
149 and 124 milliseconds
256 and 186 milliseconds
0 0 votes
Article Rating
Subscribe
Notify of
0 Comments
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x
error: Alert: Content selection is disabled!!