I need help with the following questions. How long does it take to read a disk w

Question

I need help with the following questions.

How long does it take to read a disk with 10,000 cylinders, each containing four tracks of 2048 sectors? First, all the sectors of track 0 are to be read starting at sector 0, then all the sectors of track 1 starting at sector 0, and so on. The rotation time is 10 msec, and a seek takes 1 msec between adjacent cylinders and 20 msec for the worst case.

Switching between tracks of a cylinder can be done instantaneously.

The answer is 49,999 rotations but I don't know how to get the answer

I know that my profesor said reading that Reading the first 9999 cylinders thus takes 49,995

rotations and then you add 4. However I don't know why  Reading the first 9999 cylinders thus takes 49,995 rotations

PLease help

Thanks

Explanation / Answer

So when the cylinder is switched it will take 1 rotation for seeking the sector 0 on track 0 and after that to read 4 tracks 4 more rotations will be don. So to read first cylinder 5 rotations will be done similarly to read 9999 cylinders 9999*5= 49995 rotations will be done, because cylinders are switching, right. and in the last cylinder only 4 rotation is required because no switching is required after last cylinder. Hence total rotations 49995+4= 49999.

I hope this helps.

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