History (1967): Magneto-Optical Storage Demonstrated

This article comes from the Computer History Museum.

1967: Magneto-Optical storage demonstrated
Magneto-Optical capacity outstripped magnetic disks in the 1980s

Steve Jobs introduces the NeXT workstation (October 1988)
(EDN Network, © UBM Canon)

Work on magneto-optical (MO) technologies for data storage began in the 1950s and ’60s at Bell Telephone, Honeywell, IBM, 3M, and at other labs in the U.S., Europe and Japan.

Writing and erasure of information on magneto-optical films employs a thermo-magnetic process. At ambient temperature the material has a high coercivity (a measure of the ease of magnetization) and does not respond to an applied magnetic field. When heated to the Curie-Point by a focused laser beam, the film decreases in coercivity allowing an electromagnet to reverse the direction of magnetization. Once cooled the domain is fixed and is read using the Kerr effect that senses the direction of magnetization from the rotation of a polarized beam of reflected light. Data can be erased and rewritten an unlimited number of times.

Di Chen demonstrated data storage on thin films of MnBi at Honeywell, Minneapolis, MN in 1967. Semiconductor radiation emitting diodes brought commercial drives with media based on amorphous magnetic films mounted in in removable cartridges to market in the 1980s.

Steve Jobs’ fabled 1988 presentation of a 256MB, 5.25-inch MO drive in the NeXT workstation introduced the technology to a worldwide audience. Although it was extremely reliable and offered high capacity, slow-writing made MO unsuitable for applications other than secure and archival storage. The latter were often incorporated into robotic libraries.

Many vendors of drives and media emerged, including giants HP, IBM, Kodak, Philips, Pioneer, and 3M, as well as start-ups Laser Byte, MaxOptix, MOST, and Pinnacle Micro.

5.25-inch disks offered capacities from 256MB to 9.2GB and 3.5-inch and Sony MiniDisc formats proved popular for Nintendo and other entertainment systems.

Lower cost CD/DVD drives and flash memory sticks have largely replaced MO devices.