Q. What is Access latency and Rotation Speed?

Access latency: A disk access basically moves the arm to selected cylinder and waits for rotational latency that may take less than 36ms. Latency depends upon rotation speed of disk that may be anywhere from 300 RPM to 7200 RPM. An average latency of a disk system is equal to half the time taken by disk to rotate once. Therefore average latency of a disk system whose rotation speed is 7200 RPM will be 0.5 / 7200 minutes = 4.1 ms

Rotation Speed: This signifies the speed of rotation of disk. Generally hard disks rotate at 7200 RPM (Revolution per Minute). To raise data transfer rates, higher rotation speeds or multiple R/W heads organised in parallel or disk arrays are needed.