Past exam of the year 1 of the computer science course of the University of Oxford / 2013 / Digital systems, linear algebra, introduction to formal proof / 3 / a / Solution 2026-10-31
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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
(1)
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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