GATE Overflow Test Series | Mock GATE | Test 5 | Question: 37

Question

Cylinder a disk queue with requests for $\text{I/O}$ to blocks on cylinders $191, 18, 11, 61, 137, 41, 2.$ The C-LOOK scheduling algorithm is used. The head is initially at cylinder number $100$, moving towards $0$ on its servicing pass. The cylinders are numbered from $0$ to $199$. The total head movement (in number of cylinders) incurred while servicing these requests is ________

Answer 1

Version of C-SCAN. Arm only goes as far as the last request in each direction, then reverses direction immediately, without first going all the way to the end of the disk.  
Total head movements $ = \mid 100 - 2 \mid  +  \mid 2 - 191 \mid  +  \mid 191 - 137 \mid = 98 + 189 + 54 = 341$.

So, the correct answer is $341.$

Reference: https://cse.buffalo.edu/~bina/cse421/fall2006/DiskSchedulingNov10.pdf

Comments

Sir in CLOOK it goes from 100 to max which is 191.      191-100=91

then from 191 to 2.                                                           191-2=189

then from 2 to 61.                                                              61-2=59

Total: 91+189+59=339.

 

Please reply Sir..

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Read the question carefully.

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Oh it is written that it is moving towards 0. My bad 🥺