Magnetic disc unit

DETAILED DESCRIPTION An object of the present invention is to provide a rotary recording apparatus which can, on one hand, prevent flutter causing errors in positioning from increasing even though the rotational speed becomes higher, and which can, on the other hand, enhance the degree of positional accuracy for coping with a large storage capacity.
That is, according to the present invention, there is provided a large capacity magnetic disc unit which can reduce a fluid force serving as an excitation source so as to prevent occurrence of flutter in order to restrain occurrence of noise or the like, and which can read and write data from and onto a disc with a high degree of accuracy.
Specifically, a shroud (outer wall) is provided around the entire periphery of a rotating disc, except an insertion part thereof for a carriage arm, and a gap between the shroud and the outer periphery of the disc is set to be not less than 0.
1 mm but not greater than 0.
6 mm.
An air stream induced during rotation of a disc causes a pressure differential between the upper and lower surfaces of the disc, which causes excitation of the disc, resulting in flutter of the disc.
If the gap between the shroud and the disc is set to be narrower than a predetermined value, air on the upper and lower surfaces of the disc is isolated so as to reduce the pressure differential.
With this arrangement, it is possible to reduce the amplitude of flutter, and accordingly, the degree of accuracy for positioning a magnetic head even in a high speed recording apparatus can be enhanced.