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.