__________ is the time taken to locate the disk arm to a specified track for data read/write.
Seek time
Understanding Disk Access Time Components
When a computer needs to read or write data to a hard disk drive, several steps are involved. One crucial step is moving the disk arm to the correct location on the disk surface where the data is stored. This movement is what the question is asking about.
Let's break down the components of disk access time to understand which one fits the description:
- Seek time: This is the time it takes for the read/write head, which is attached to the disk arm, to move from its current position to the track (concentric circle on the disk) where the desired data is located. The further the arm needs to move, the longer the seek time.
- Transfer Time: This is the time it takes to actually read the data from or write the data to the disk surface once the head is on the correct track and sector. It depends on the speed of the disk rotation and the amount of data being transferred.
- Rotational delay (or latency): Once the disk arm is on the correct track, the system must wait for the desired sector (a division of the track) to rotate under the read/write head. This waiting time is the rotational delay. On average, this is half the time for a full rotation.
- Disk Access Time: This is the total time required to access data on the disk. It is generally considered to be the sum of seek time, rotational delay, and transfer time.
Based on these definitions, the time taken specifically to move the disk arm to a specified track is the seek time.
Comparing Disk Access Time Components
Here's a simple comparison of the times involved in disk access:
| Component | Description |
|---|---|
| Seek Time | Time to move arm to the correct track. |
| Rotational Delay | Time to wait for the correct sector to rotate under the head. |
| Transfer Time | Time to read or write the data. |
| Disk Access Time | Total time (Seek + Rotational Delay + Transfer). |
The question specifically asks about the time to locate the disk arm to a specified track, which directly corresponds to the definition of seek time.
Revision Table: Key Disk Terms
| Term | Meaning |
|---|---|
| Track | A concentric ring on the disk surface. |
| Sector | A segment or division of a track. |
| Cylinder | A set of tracks at the same radial position on all disk surfaces. |
| Disk Arm | Mechanical arm holding the read/write heads. |
| Read/Write Head | Component that reads data from or writes data to the disk surface. |
Additional Information on Disk Access Time Calculation
The total disk access time can be represented by the formula:
\( \text{Disk Access Time} = \text{Seek Time} + \text{Rotational Delay} + \text{Transfer Time} \)
Understanding these individual components is essential for evaluating the performance of a hard disk drive. Seek time is often the most significant factor contributing to the total access time, especially for random data access.
Important Questions from Secondary Memory
Which of the following can be said about primary storage in comparison with secondary storage?
For a magnetic disk with concentric circular tracks, the seek latency is not linearly proportional to the seek distance due to
If one track of data can be transferred per revolution, then what is the data transfer rate ?
Given below are two statements:
Statement I: The disk has a total number of 2000 cylinders.
Statement II: 51200 bytes is not a valid block size for the disk.
In the light of the above statements, choose the correct answer from the options given below:
If T is the capacity of a track in bytes, and S is the capacity of each surface in byte, then (T, S) = _____.
