Aluminium alloys are widely used as a substrate in magnetic disks, but the demand for higher storage and faster access times require better materials. A replacement material would need to offer a thinner substrate, a higher recording density, a very smooth surface, and a high degree of flatness.

Originally platinum alloys were considered to be a solution, but drives built with the alloys suffered from electrolytic corrosion caused by interactions between the magnetic film and the substrate.

Yamamura Glass Company believes that glass can replace aluminium. Glass is known for its excellent chemical durability, mechanical strength, heat resistance, surface flatness and surface smoothness. Patent 5691256 describes a process to improve two types of glass substrate for magnetic disks, a ion exchange glass and a glass-ceramic.

These types of glass generally cause deterioration of the magnetic film due to alkalis in the material. Yamamura's invention is related to a new set of glass compositions, and the way in which they are heated, polished and chemically treated. The process limits the degradation of the magnetic film, without losing the traditional advantages of the material, thus making it the perfect compound for use as a substrate.