Abstract: Gain information in a read amplifier, which is recorded when data to be measured is reproduced, is stored in an AGC control memory circuit in advance. By reproducing the data using the gain information, reproduced data varied according to the amount of flotation of a magnetic head and the position of the magnetic head alone can be obtained. A variation in voltage amplitude of the reproduced data is detected by an envelope signal generating circuit and a variation in phase difference between a reading cycle in which the reproduced data is read and a reference cycle is detected by a phase difference signal generating circuit. A calculator calculates a float interval of the magnetic head and a variation in the position thereof based on these detected variations. As a result, a decision can be made as to whether the float interval of the magnetic head and the variation in the position thereof exceed an allowable range.

Abstract: Magnetic disk unit 1 is connected to personal computer 400 through recording mode selecting means 2, and recording mode selecting means 2 can select one of 3 recording modes (high reliability, large capacity, and high speed) and magnetic disk unit 1 records information with the recording method selected by recording mode selecting means 2. The controllability of the magnetic disk unit 1 and personal computer 400 is improved significantly by selecting the most suitable recording method according to the characteristics of information to be recorded.

Abstract: A magnetic disk apparatus includes a magnetic disk, a magnetic head which performs information recording and reproducing for the magnetic disk, a load spring for supporting the magnetic head, a head arm for fixing the load spring, a housing for housing these components, a shaft which fixes the head arm, bearings for supporting the shaft rotatably on the housing, and a motor which is coupled to the shaft. The motor comprises a motor cover, a permanent magnet which is divided into a plurality of segments and fixed on the shaft, and a coil which is fixed on the interior surface of the motor cover by being spaced with a certain gap from the permanent magnet. The shaft is included with a counter weight so as to complement the weight of the head arm, load spring and magnetic head. The coil has linear conductor sections parallel to the shaft, with the total number of linear sections being set equal to the total number of segments of permanent magnet.

Abstract: A thickness shear quartz crystal oscillator has two major surfaces which extend in the direction the of X axis of the crystal and which are 5mm to 10mm long. X-Z plane defined by the X axis and Z axis of the crystal is rotated about the X axis by 35.degree.08' to 35.degree.16' so that the major surfaces are parallel to an X-Z' plane defined by the X axis and an imaginary Z' axis inclined to the Z axis at 35.degree.08' to 35.degree.16'. One of the major surfaces is displaced in the direction of the Z' axis to thereby cause the side faces of the oscillator to incline at an angle of 4.degree. to 6.degree..