A floppy disk drive incorporates a cantilevered arm carrying at its free end a floppy disk positioning and clamping cone, the arm being pivotally mounted along the rear edge of the disk drive base frame. A longitudinal control shaft, rotatable by a control lever on the front panel of the drive, includes a cam riding in contact with a cam surface in a central region of the arm. The rear extremity of the control shaft is journaled in a variable height bearing block mounted on the base frame. A single screw controls the height of the bearing block and thus the clamping pressure exerted by the positioning and clamping cone on the floppy disk, which pressure may thereby be precisely and quickly adjusted. The invention is especially advantageous in half-height, direct drive floppy memory apparatus in which height and spindle torque limitations impose substantial design, fabrication and servicing constraints.The invention also provides for easy yet precise adjustment of the timing of the output pulse of a photosensor used to detect a sector index hole in the floppy disk.