QUESTION 1 a) Disk requests come into the disk driver for cylinders: 86, 1470, 9

Question

QUESTION 1

a) Disk requests come into the disk driver for cylinders: 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130 in that order. The disk has 5000 total cylinders (numbered 0 to 4999) and the disk head positioned over cylinder 143 and previous request was at cylinder 125. What is the sequence of reads and calculate the total distance the read/write head will traverse using Shortest Seek Time First and SCAN algorithms?

b) What are the short comings of shortest seek time first (SSTF) disk scheduling algorithm?

c) What is a bootstrap program, and where is it stored?

Note: Do not write the answer in your handwriting and the answer should be non-replicated from the site.

Explanation / Answer

Solution:

a)

Number of total cylinders in the disk= 5000

The requests for the cylinder is

86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130

currently at 143 and previous was 125

The sorted order of cylinders will be

86 130 143 913 948 1022 1470 1509 1750

Shortest seek time first

In shortest seek time first wherever the time difference is shortest, the memory request will be read and completed

So, now

the order of execution will be

143 130 86 913 948 1022 1470 1509 1750

The total distance will be

143-130 = 13

130-86 = 44

913-86= 827

1750-913 = 837

Total distance = 837+827+44+13= 1721

In SCAN the memory requests are read towards the biggest cylinder first then the header will rollback towards the smallest disk cylinder request and finish the rest.

86 130 143 913 948 1022 1470 1509 1750

The order will be

143 913 948 1022 1470 1509 1750 130 86

Total distance = 1750-143+1750-86= 3271.

b)

There is a chance of starvation for the disk cylinder which is placed very far from the position of the head if the disk requests keep on coming.

c)

A bootstrap is a program that initializes the operating system (OS) during startup. It is located in the Bootstrap Loader.

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