Question

Suppose that a 10 MB file is stored on a disk on track number 50 in consecutive sectors. The disk arm is currently situated over track number 100. Assume that moving the arm from one cylinder to the next takes about 1 ms and it takes about 5 ms for the sector where the beginning of the file is stored to rotate under the head. Also assume that reading occurs at a rate of 100 MB/s. How long will it take to retrieve the file from the disk?

Answer 1

To retrieve the 10 MB file from the disk, it will take a total of 200.1 ms, considering the time to move the arm to the correct track, the time for the sector to rotate under the head, and the time to read the file.

Step-by-step explanation:

To calculate the time it will take to retrieve the file from the disk, we need to consider the time it takes for the disk arm to move to the correct track, and the time it takes for the sector where the file is stored to rotate under the head. Let's break it down:

1. Time to move the arm to track 50: since the current track is 100 and the track to move to is 50, we need to move the arm 50 tracks. Each track takes 1 ms to move, so it will take a total of 50 ms.

2. Time for the sector to rotate under the head: the disk rotates at a rate of 1000 rpm. This means it takes 1/6000 minutes to complete one rotation (1 minute / 1000 rpm). Since there are 60 seconds in a minute, it takes 1/6000 * 60 = 0.01 seconds for the disk to rotate one sector. This means it will take a total of 0.01 * 10 sectors = 0.1 seconds for the sector where the file is stored to rotate under the head.

3. Time to retrieve the file: the file size is 10 MB and the reading rate is 100 MB/s. To calculate the time, we divide the file size by the reading rate: 10 MB / 100 MB/s = 0.1 seconds.

Adding up the time it takes for the arm to move to track 50, the time for the sector to rotate, and the time to retrieve the file, the total time to retrieve the file from the disk is 50 ms + 0.1 seconds + 0.1 seconds = 200.1 ms.