Magnetic disks used to store information on a PC are made by coating a magnetic substance onto a glass substrate. Magnetic disks which have been expected to expand demands are installed not only in PCs, but car navigation systems, servers, and video games
Even minute degrees of unevenness on the surface of a glass substrate could badly affect the coating of the magnetic substance and therefore glass substrates need to be manufactured with utmost precision. Accordingly, the glass substrate is said to be one of the most difficult glass product to manufacture, and it was taken for granted to use arsenic and antimony as additives essential in the removal of small bubbles from glass. However, the AGC Group became the pioneer successfully develop arsenic- and antimony-free glass substrates for hard disk drive, and has provided them to customers.

Structure of a hard disk drive