unacademy aimt 2023 mock 1

Question

A floppy disk has 40 cylinders. When storing a file on the floppy disk, the operating system (probably the floppy device driver) often attempts to put the blocks of the file in cylinders that are close to one another (if this can be accomplished). Assume that if the operating system does not attempt to cluster related blocks, two blocks that are logically consecutive are stored about 13 cylinders apart, on average. However, if the operating system makes an attempt to cluster related blocks, the mean interblock distance can be reduced to 2 cylinders. How long does it take to read 100 block file in each case, if a seek takes 6 milli-seconds per cylinder moved, the rotational latency is 20 milli-seconds on average, and the transfer time is 15 milliseconds per block?

Comments

What is a floppy disk?

Answer 1

Total time = seek time + rotational time + transfer time

In the first case: two blocks that are logically consecutive are stored about $13$ cylinders apart, on average. 

$100 * (13*6ms + 20ms + 15 ms)$ = $11300$ $milliseconds$ = $11.3$ $seconds$

(for each block we have to consider the $(seek time + rotational$ $time + latency$ $time)$, because blocks to be fetched are not contiguous here).

In the second case:  the mean inter block distance can be reduced to $2$ cylinders.

$100* (2*6ms + 20 ms + 15 ms) = 4700$ $milliseconds = 4.7$ $seconds$

 

 https://efreidoc.fr/L3/Operating%20System/Assignments/2009-10/2009-10.assignments.homework2.answers.op.pdf