Difference between Seek Time and Transfer Time in Disk Scheduling

In hard drives, an head is present which is supposed to write or read from the magnetic disk, in this article, I am going to refer it as head.

Seek Time:
It is the time that is taken by the head of a disc to move from one track to another track on a disk. Seek Time can vary a lot upon where the head is present right now when the read/write request is sent, hence Average Seek Time is used more widely.

For a clearer picture, consider a hard-disk of concentric circle called tracks, Suppose you want to fetch some data. Seek Time is the time need for the head to move from its current track to the one where the data is present, Even after this it might have to wait for some more time because the data is present in the opposite side of the track and this delay is called Rotational Latency but this isn’t counted in Seek Time.
Depends on:

  • Speed of read/write head
  • Distance between current and final position

Transfer Time:
Transfer time is the time taken to transfer the data from the disk. It varies on the rotational speed of the disk, the faster a disk rotates the faster we can read data and on the Number of bytes on one track which can also be called the density of the disk, the more the faster we can transfer data hence lower transfer time.
Depends on:

  • Rotational Speed of a disk, faster is better
  • Track and Sector Density, more is better
  • Amount to data to be Transfered

S.NO. Seek Time Transfer Time
1 Time taken by the head to more from current track to the one where data is present. Time taken to transfer data from the disk to the host system.
2 Can varry a lot depending upon the distance between current and final position and how it has been instructed to go. T = b/rN
T is Transfer time, b is number of bytes to be transfered, N is number of bytes on a track and r is rotational speed in Rps
3 Measure in Average Seek Time Measure in Data Transfered in a unit time i.e. Second
4 Usually in between 10-20 ms, depending upon the RPS and grade of Drive It takes about 1 sec to transfer 30-60MB of data

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