Patent ID: 9437235
Filing Date: 2016-09-06
CPC Classification: C03C,G11B

Claim Text:
1. A hard disk drive, comprising: a magnetic disk that includes: a glass substrate for an information recording medium, the glass substrate including a surface having an arithmetic mean roughness (Ra) deviation rate of 3% or less, wherein the Ra deviation rate is calculated based on arithmetic mean roughness (Ra) values measured using an atomic force microscope at 10 or more different measurement fields on the surface of the glass substrate, each measurement field having 10 μm×10 μm, and wherein the Ra deviation rate is the ratio of the number of measurement fields, each having an Ra value that differs by 0.1 nm or greater relative to a totality mean value of Ra values for all of the 10 or more measurement fields, to the number of the 10 or more measurement fields, each Ra value being 1.5 nm or less, the surface having a maximum peak height (Rp) of 10 nm or less, and the ratio of Rp/Ra being 10 or less; a magnetic film formed on a surface of the glass substrate; and a head operable to record information on the magnetic disk and to read information from the magnetic disk.