UGC NET CSE | June 2012 | Part 3 | Question: 74

Question

On a disk with 1000 cylinders (0 to 999) find the number of tracks, the disk arm must move to satisfy all the requests in the disk queue. Assume the last request service was at track 345 and the head is moving toward track 0. The queue in FIFO order contains requests for the following tracks:

123, 874, 692, 475, 105, 376

(Assume scan algorithm)

• A. 2013
• B. 1219
• C. 1967
• D. 1507

Answer 1

FIRST LOOK AT THIS :http://www.cs.iit.edu/~cs561/cs450/disksched/disksched.html

ANS IS OPTION B .1219

345-----123(222)

            -------------------105(18)--------0(105)

                                                     .-----------------376(376)-------------475(99)-----------692(217)------------874(182)

(  ) VALUES ARE THE DISTANCES 

SO TOTAL ARM MOVE =    222+18+105+376+99+217+182=1219

Comments

What about FIFO order. Will scan algo not satisfy this order.

Answer 2

(345-123)+(123-105)+(105-0)+(999-0)+(999-874)+(874-692)+(692-475)+(475-376)

=222+18+105+999+125+182+217+99

=1967

Comments

What you have done is CSCAN

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you are right

Answer 3

my answer

Comments

Answer will be option A.

The question is hinting to use FCFS algorithm not C-SCAN or C-LOOK!

Answer 4

Answer will be option A.

The question is hinting to use FCFS algorithm not C-SCAN or C-LOOK!

Comments

But initial value not given how we can take 345 initial track??????