#90 IBM 350 RAMAC Disk File


World's first computer storage device with random access to large volumes of data

The IBM 350 disk drive storage development led to the breakthrough of on-line computer systems by providing the first storage device with random access to large volumes of data. Since its introduction on September 4, 1956, it has become the primary computer bulk-storage medium, displacing punched cards and magnetic tapes and making possible the use of the computer in such areas as airline reservations, automated banking, medical diagnosis, and space flights.

Fifty disks stacked on a cantilevered, rotating spindle recorded in one hundred concentric tracks on each side of each disk, providing 5 million characters of data storage. Developments, such as the pressurized-air head bearing, made disk storage feasible. Access to any of the 20,000 tracks could be obtained mechanically through an access arm under servo control that would move two read/write heads to the desired disk.

Development of the disk drive was pioneered by IBM engineers in San Jose and led to IBM's first computer manufacturing plant in California.

Engineers test units of the 350 RAMAC System

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For More Information

IBM Building 12
5600 Cottle Road
San Jose, CA 95193

Useful Links

IBM History site

Ceremony Notes

February 1984. Plaque is mounted in lobby of building 12 at the beginning of the historical display of the disk drive.

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