A factor of data access time due to disc rotation. The faster a disc spins the quicker it will be at the position where the required data can start to be read. As disc diameters have decreased, so rotational speeds have tended to increase but there is still much variation. Modern 3-1/2- inch drives typically have spindle speeds of between 3,600 and 7,200 revolutions per minute, so one revolution is completed in 16 or 8 milliseconds (ms) respectively. This is represented in the disc specification as average latency of 8 or 4 ms.