Patent ID: 8124258
Filing Date: 2012-02-28
Classification: C03C,G11B

Abstract:
1. A glass substrate for a magnetic disk, comprising: a hole and an annular area concentrically positioned around the hole, the annular area having a width of 30 μm on a main surface on which a magnetic recording area is formed, a plurality of circumferential unit areas within the annular area, the unit areas each having a same radius from the hole and a circular arc length of 30 μm, and bumps provided in any area within the annular area, wherein a difference in arithmetic average roughness values between different unit areas of the unit areas within the annular area, the different unit areas being positioned 180° from each other along a circular path of the annular area, is 0.2 nm or smaller, the bumps from a roughness pattern having a roughness period of smaller than 2 μm, the bumps have a maximum height of 6 nm, and a number of the bumps having a height of 3 nm or higher is one or less.