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Which of the following statements is not true about disk-arm scheduling algorithms ? 

  1. SSTF (shortest seek time first) algorithm increases performance of FCFS.
  2. The number of requests for disk service are not influenced by file allocation method.
  3. Caching the directories and index blocks in main memory can also help in reducing disk arm movements.
  4. SCAN and C-SCAN algorithms are less likely to have a starvation problem. 
in Operating System by Boss (30.8k points)
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2 Answers

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Ans is B

A)is true 

B)is NOT CORRECT  as the  number of requests for disk service can be greatly influenced by file allocation method.e.g a program reading contiguous allocated file will generate several requests that are closed together on the disk hence minimal head movement . on the other hand linked file or indexed file may include scattered block which need more head movement

C)is TRUE Caching the directories and index blocks in main memory can also help in reducing disk arm movements especially for read operation.

d)is TRUE as SCAN & C-SCAN are less likely to be suffer from starvation as they move in both direction irrespective of type of request. SSTF may suffer from starvation

by Boss (49.3k points)
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+1
SSTF performs better but it is not optimal..

http://www.cs.iit.edu/~cs561/cs450/disksched/disksched.html
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In the disk-arm scheduling algorithms The number of requests for disk service are highly influenced by file allocation method.
The time required to read or write a disk block determined by 3 factors.
Seek time: The time to move the arm to the proper cylinder.
Rotational delay: the time for the proper sector to rotate under the head.
Actual data transfer time
Among these, the Seek time dominates.

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