Patent ID: 8241768

Claim:
A magnetic disk substrate being a disk-shaped and polished glass substrate and having a generally flat main surface, an end face, a chamfered face formed between the main surface and the end face, and an offset portion, at a periphery of the main surface, raised or lowered with respect to a flat surface, other than the periphery, of the main surface, wherein: said substrate is polished such that a magnitude of offset of said offset portion is substantially uniform over an entire circumference of said substrate such that when measuring said offset portion of said substrate at 12 points per 30° in a circumferential direction, a change in magnitude of the offset is 5 nm or less; and an extreme portion, where rising or lowering is maximum in said offset portion, is present in a range of 92.0% to 97.0% with respect to a distance to the end face from a center of said substrate.