= Solution
A <hard disk drive> pays substantial <seek time> to position the head and <rotational latency> to reach the desired sector. After that positioning, neighboring bytes stream past the head quickly. A larger transfer therefore amortizes positioning and command overhead over many bytes.
The physical sector also needs framing, synchronization and error-correcting redundancy. Transferring one byte at a time would spend an excessive fraction of the medium and controller work on that overhead. A controller buffer and a block transfer can efficiently deliver the sector to <computer memory>, often using <direct memory access>.
Thus
$$
\boxed{\text{larger transfers amortize positioning, framing and command costs}.}
$$
The choice is a compromise: excessively large blocks waste transfer time for small requests and can increase <internal fragmentation> in a <file system>.
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