An actuator system for a reduced-head hard disk drive, the system comprising: a ball screw cam assembly comprising: a hollow screw comprising x number of starts, a ball bearing assembly comprising x number of balls, wherein x is three or greater and wherein each ball rides in a corresponding start; a retaining ring holding the x number of balls in equal spacing, in a respective start of the x number of starts, about an outer periphery of the screw; and an actuator arm coupled with the ball bearing assembly; wherein the actuator arm translates along an axis of the screw upon rotation of the screw; and characterised by: the starts being tapered so as to function as upper and lower portions of an inner race of the ball bearing assembly, wherein the outer race of the bearing assembly is a 2-part race, comprising a tapered inner surface of an opening in the actuator arm as a lower outer race surface and comprising a bearing half-race with a tapered lower surface thereof providing the upper outer race surface, or wherein the outer race of the bearing assembly is a 2-part race, comprising a tapered half-race (202d-1) as a lower outer race surface and a tapered half-race (202d-2), bonded to the actuator arm, as an upper outer race surface, together forming a v-notch outer race which results in a radial preload at four points of contact via the inner and outer races while an elastomeric O-ring or a wavy washer, functioning as a metallic spring is provided as a spring to provide a variable compression force applied to the 2-part race (205a,202d; 202d-1,202d-2); and wherein the system further comprises a stepper motor disposed within and coupled with the screw, wherein the stepper motor drives the rotation of the screw. a hollow screw comprising x number of starts, a ball bearing assembly comprising x number of balls, wherein x is three or greater and wherein each ball rides in a corresponding start; a retaining ring holding the x number of balls in equal spacing, in a respective start of the x number of starts, about an outer periphery of the screw; and an actuator arm coupled with the ball bearing assembly; wherein the actuator arm translates along an axis of the screw upon rotation of the screw; and characterised by: the starts being tapered so as to function as upper and lower portions of an inner race of the ball bearing assembly, wherein the outer race of the bearing assembly is a 2-part race, comprising a tapered inner surface of an opening in the actuator arm as a lower outer race surface and comprising a bearing half-race with a tapered lower surface thereof providing the upper outer race surface, or wherein the outer race of the bearing assembly is a 2-part race, comprising a tapered half-race (202d-1) as a lower outer race surface and a tapered half-race (202d-2), bonded to the actuator arm, as an upper outer race surface, together forming a v-notch outer race which results in a radial preload at four points of contact via the inner and outer races while an elastomeric O-ring or a wavy washer, functioning as a metallic spring is provided as a spring to provide a variable compression force applied to the 2-part race (205a,202d; 202d-1,202d-2); and wherein the system further comprises a stepper motor disposed within and coupled with the screw, wherein the stepper motor drives the rotation of the screw. the starts being tapered so as to function as upper and lower portions of an inner race of the ball bearing assembly, wherein the outer race of the bearing assembly is a 2-part race, comprising a tapered inner surface of an opening in the actuator arm as a lower outer race surface and comprising a bearing half-race with a tapered lower surface thereof providing the upper outer race surface, or wherein the outer race of the bearing assembly is a 2-part race, comprising a tapered half-race (202d-1) as a lower outer race surface and a tapered half-race (202d-2), bonded to the actuator arm, as an upper outer race surface, together forming a v-notch outer race which results in a radial preload at four points of contact via the inner and outer races while an elastomeric O-ring or a wavy washer, functioning as a metallic spring is provided as a spring to provide a variable compression force applied to the 2-part race (205a,202d; 202d-1,202d-2); and wherein the system further comprises a stepper motor disposed within and coupled with the screw, wherein the stepper motor drives the rotation of the screw.