Disk access timing: The total time to prepare and retrieve a block for reading from a magnetic disk is composed of which elements?

Introduction / Context:Disk performance analysis relies on understanding the separate contributors to delay: seek time, rotational latency, and transfer (transmission) time. Many definitions distinguish between the time to position the head (prepare) and the time to actually transfer data once positioned.

Given Data / Assumptions:

• Seek time moves the read/write head radially to the target track.
• Rotational latency is the wait for the desired sector to rotate under the head.
• Transmission (transfer) time is the actual data movement once the head is over the sector.

Concept / Approach:

If the question emphasizes “prepare a disk drive mechanism for a block of data to be read,” the preparation is complete when the head is in position and the correct sector is under the head. That comprises seek time + rotational latency. Transfer time begins after preparation, during the actual reading of the block.

Step-by-Step Solution:

Verification / Alternative check:

Storage texts define access time as seek + latency, and total service time as access time + transfer time. The wording “prepare the mechanism” maps to access time.

Why Other Options Are Wrong:

• Latency alone: Ignores track seek.
• Latency + transmission: Missing seek, and includes transfer.
• Latency + seek + transmission: That is total service time, not just preparation.
• None of the above: Incorrect because seek + latency is correct.

Common Pitfalls:

Using “access time” and “transfer time” interchangeably; forgetting that large sequential reads amortize seek/latency over many blocks.

Final Answer:

latency plus seek time