storage, hardware
The time for the start of the required sector on a disk to appear underneath the read/write head. The worst case is where it has just passed the head when the request is received. For a disk drive with N heads per surface, rotating at R revolutions per minute, the average rotational latency will be
L = 30/NR seconds.
Rotational latency is one component of access time.
(2009-11-06)