Abstract: A transient temperature compensation system for use in a magnetic disk drive comprised of both fixed and removable disks. The system includes first and second thermistors respectively mounted immediately adjacent the fixed and removable disks. The second thermistor is preferably mounted for movement between an operative position and an inoperative position. In the operative position, the thermistor is positioned in very close proximity to the disk. In the inoperative position, the thermistor is spaced from the disk to permit sufficient clearance to enable the disk to be removed from the drive. The outputs of the two thermistors are used to develop a signal representing the temperature differential between the two discs which signal is supplied to the disk drive head positioning system. This signal is used to modify the positioning of the heads relative to the fixed disk to compensate for differences in the radial positions of corresponding tracks on the fixed and removable disks.

Abstract: Apparatus for detecting the direction of motion from a reference signal, R, and a quadrature signal, Q, derived from the output signals X+0 and X+90 of a position transducer, wherein the polarity of the reference signal alternates with every fixed increment of motion of a transducer and the quadrature signal which maintains phase difference of +90.degree. or -90.degree. with respect to the reference signal depending on the direction of motion, is comprised of: digital means for producing a narrow pulse, P, at each low-to-high transition of the quadrature signal and a narrow pulse, N, at each high-to-low transition of the quadrature signal; means for determining the direction of motion from these narrow pulses and the reference signal once during each half cycle of the reference signal, and means for storing this direction information until a subsequent determination is made in order to provide a continuous signal indicating the direction of motion.