Description of access time in terms of latency (rotational delay), seek time and transfer time.

Disk access time can be calculated by adding up the 'seek time' and the average 'latency time'
  • Seek time: the time needed for the read/write arm to look for the desired track
  • Latency time (also called rotational delay): the time it takes for the desired sector on the track to spin around to the read/write arm (since the piece of data required might be on the other side of the disk relative to the read/write at the moment).
  • Transfer time: the time a hard disk drive needs to read and transmit one block of data
  • Disk access time in hard disk drives is measured in milliseconds
    • Even though this might seem fast, CPUs are still able to calculate much faster than this, causing hard disk drives to be slow in comparison

Disk access time = seek time + latency time + transfer time

Written by Jocbe
Last Update: 24. September 2010

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