US Patent 7985494 Glass substrate for magnetic disk and magnetic disk apparatus

A glass substrate for a magnetic disk satisfies Ra1≦0.8 [nm], 0 [nm]≦Ra1−Ra2≦0.2 [nm], Wa1≦0.6 [nm], and 0 [nm]≦Wa2−Wa1≦0.2 [nm]. Ra1 is an average surface roughness of a first annular area between 1 mm and 3 mm outward from an inner periphery of a main surface of the glass substrate, Ra2 is an average surface roughness of a second annular area between 1 mm and 3 mm inward from an outer periphery of the main surface, Wa1 is an average waviness of the first area in a circumferential direction of the glass substrate having a cycle of 300 μm to 5 mm, and Wa2 is an average waviness of the second area in the circumferential direction having a cycle of 300 μm to 5 mm.