Abstract: A method of measuring a linear velocity of a rotating disk on a disk drive system wherein a rotation of a spindle motor is controlled in accordance with a predetermined linear velocity which is generated based on a signal reproduced from the disk to control the initial rotation of the spindle motor. The linear velocity of the disk is determined by measuring one revolution of the disk and from the radius of the disk. The disk drive system includes a servo control system to measure the one revolution of the disk and to generate a servo control signal at a time corresponding to a predetermined number of output pulses from the spindle motor measured during the one revolution time of the disk. The servo control signal is supplied to the spindle motor to control its initial rotation.