Abstract: This system moves magnetic tape past the read/write head at a constant velocity by separately servo controlling the source reel motor and the take-up reel motor. Separate fine encoders are associated with each reel, each encoder providing multiple pulses for each revolution of the respective reel. Two radius calculation circuits each receive pulses from a respective one of the encoders and each calculate therefrom the radius values of tape on both of the reels. A radius information selector then selects, for use in controlling the motors, that set of radius values which is calculated by the calculation circuit which is receiving encoder pulses at the greater sampling rate. Separate servo circuits drive the two motors at respective angular velocities determined by utilizing the selected set of radius values. In each drive circuit, the associated tape radius is multiplied by the actual reel angular velocity, as indicated by the time duration between consecutive pulses from the encoder associated with that reel.