The Seek Latency in Magnetic Disk with Concentric Circular Tracks

The seek latency refers to the time it takes for the read/write head of a magnetic disk to move from one track to another on the disk. In a magnetic disk with concentric circular tracks, the seek latency is not linearly proportional to the seek distance. This is primarily due to the arm starting and stopping inertia.

Arm Starting and Stopping Inertia

When the read/write arm of a magnetic disk starts moving, it takes some time to reach its full speed. Similarly, when the arm stops moving, it takes some time to come to a complete stop. This inertia of starting and stopping affects the seek latency.

Explanation

To understand why the seek latency is not linearly proportional to the seek distance, let's consider the scenario of moving the read/write head from the innermost track to the outermost track.

- When the arm starts moving from the innermost track, it takes some time to accelerate and reach its maximum speed. During this acceleration phase, the seek latency increases.
- Once the arm reaches its maximum speed, the seek latency remains relatively constant as the read/write head moves across the tracks.
- However, when the arm nears the outermost track and needs to decelerate to come to a stop, the seek latency increases again. This deceleration phase adds additional time to the seek operation.

This non-linear relationship between seek latency and seek distance can be visualized by imagining the movement of the arm as a graph. The graph would show a curved line, indicating that the seek latency increases more rapidly towards the ends of the tracks.

Effects of Arm Starting and Stopping Inertia

The arm starting and stopping inertia in a magnetic disk results in a longer seek latency for larger seek distances. This means that the time it takes to move the read/write head from one track to another increases more than proportionally with the increase in seek distance.

This non-linearity in seek latency can impact the overall performance of the disk system. For example, if there are frequent requests for data that are located far apart on the disk, the increased seek latency can lead to slower access times and decreased disk performance.

Conclusion

In summary, the seek latency in a magnetic disk with concentric circular tracks is not linearly proportional to the seek distance due to the arm starting and stopping inertia. This inertia causes the seek latency to increase more rapidly towards the ends of the tracks, resulting in a non-linear relationship between seek latency and seek distance.