Self Doubt regarding C-SCAN

Question

Consider a disk has 200 cylinders, numbered from 0 to 199. At some time the disk arm is at cylinder 100, and moving towards right direction. There is a queue of disk access requests for cylinders 30, 85, 110, 100, 105, 126, 135, 55 and 195. The difference in the distance that will be traversed by the R/W head when the LOOK algorithm is used compared to the CSCAN algorithm is ________.

Please also mention the method of C-SCAN.

Comments

@srestha 

C-SCAN:- (199-100)+(199-0)+(85-0)= 383

LOOK=(195-100)+(195-30) = 260

diff = 383-260 =  hence 123

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yes,correct answer is 123.

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http://www.cs.iit.edu/~cs561/cs450/disksched/disksched.html

in CSCAN the jump between extreme ends isn't counted

LOOK=>260 tracks

CSCAN=>184 tracks

difference=>76

Answer 1

Is my answer is correct?

I got : CSCAN--380

And Look-- 260

Difference- 120

Answer 2

I got : CSCAN - 383

And Look 260

Comments

Someone please explain with figure

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C scan - 383

Look-260

Difference is 123

Answer 3

The answer is 123

Answer 4

Diff is 123.