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At constant transfer rate $v$ bytes per second, moving $B$ bytes takes $B/v$ seconds. The size and rate must use compatible units. This term alone does not include seek time, rotational latency or controller setup costs.

Choose the order of pending input-output requests. Physical head movement, rotational latency, request arrival times and fairness can favour different orders. A seek distance calculation is a simplified model; real seek time is not necessarily linear in track displacement.

A data storage device that records information magnetically on rotating platters. Accessing a sector can require moving a head to its track, waiting for the sector to rotate beneath it, and transferring the data. These contributions are seek time, rotational latency and data transfer time.^[ref]

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.

ThusThe choice is a compromise: excessively large blocks waste transfer time for small requests and can increase internal fragmentation in a file system.

Reusing a block-oriented file system preserves existing operating-system interfaces, tools, consistency procedures and on-disk formats. It also permits common buffering and caching policies. Large transfers can still amortize software and controller overhead, and flash memory itself has page-program and erase-block constraints, so a block device abstraction is often useful even without mechanical motion.

The costs are that a fine-grained change may require reading and rewriting a larger logical block, and a small computer file can waste part of its final file data block. Structures optimized to reduce seek time need not be best for non-volatile memory. For flash memory, repeated metadata updates and erasing or relocating larger regions can increase physical writes and consume finite program/erase endurance. A translation layer can hide these constraints but adds mapping space and work.

ConsequentlyThe balance depends on the actual medium: byte-addressable non-volatile memory and page/erase-based flash memory have different physical constraints.

At 6000 revolutions per minute the disk makes 100 revolutions per second, so one turn takes 10 ms and the mean rotational latency is 5 ms. Adding seek time, data transfer time and controller overhead gives, using decimal MB,Using $1\mathrm{MB}=2^{20}$ bytes instead gives 19.09765625 ms, with the same rounded answer. The calculation assumes the stated rate applies to the sector transfer and that the seek and overhead are each paid once.