Disk Block Access Time
Time for the disk head to move to the correct track.
Time for the beginning of the correct sector to spin round to the head. (Some authors use “latency” as the term for this component, or they use latency to refer to all of what we are calling seek time.)
Time to read or write the data.
(Approximately the time for the sector to spin by the head).
For a 7200 RPM hard disk with 8 millisec seek time, average access time for a block is about 12 millisec.
(see Albert Drayes and John Treder: http://www.tanstaafl-software.com/seektime.html)