Patent ID: 7727645

Claim:
A magnetic recording medium substrate product comprising a disk-shaped non-magnetic substrate which comprises: (1) a circular hole in a center portion thereof; (2) a main surface on which a magnetic layer is to be formed; (3) an outer end surface; (4) an inner end surface defining the circular hole; (5) a chamfer formed at least one of a first portion between the main surface and the outer end surface and a second portion between the main surface and the inner end surface; and (6) a curved surface (R surface) having a radius of 0.01 mm to 0.05 mm, which is formed at a corner portion between the main surface and the chamfer, wherein the chamfer has a surface roughness (Ra) falling within a range of 4.0 Å≦Ra≦100 Å as measured by means of an AFM, and the curved surface has a surface roughness (Ra) falling within a range of 4.0 Å≦ Ra≦50 Å as measured by means of an AFM and wherein the non-magnetic substrate is formed of any of amorphous glass, crystallized glass and silicon.