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History (1980): Seagate 5.25-Inch HDD Becomes PC Standard

With ST506 interface

This article comes from the Computer History Museum.

1980: Seagate 5.25-inch HDD becomes PC standard
Personal computer boosts HDD output to new levels of production

Seagate ST-506 5MB HDD Interior
(Seagate Technology)

Reviewing the history of the disk drive market in 1998, industry analyst Disk/Trend president James Porter described the 1980 introduction of the Seagate ST506 5.25-inch 5MB unit as the model “that created the biggest change in the industry.

Incorporated in 1978 by Finis Conner, Syed Iftikar, Doug Mahon, Tom Mitchell, and Al Shugart, Seagate Technology designed ‘Winchester’ technology HDDs matching the physical size of the Shugart Associates ‘Minifloppy’ drive to serve the booming desktop PC market.

This introduction established ST506 interface and form factor as industry standards. It also established Seagate as an instant leader in the industry.

Tandon shipped a competing 5.25-inch model that same year. Ten more manufacturers shipped in 1981, including units licensed from Seagate by Texas Instruments and Honeywell Bull. With the 10MB ST412 introduced in late 1981, Seagate became a major supplier to the XT, IBM’s first PC containing an HDD. Following the IBM AT in 1984, HDDs came as standard equipment on all new personal computers.

To serve smaller and portable PCs, in 1983 Rodime, Glenrothes, Scotland introduced the first 3.5-inch HDD, the R0351/352, units that used a smaller media diameter and matched the industry standard 3.5-inch floppy disk form factor. Rodime was followed quickly by Microcomputer Memories, Microscience International, and MiniScribe. John Squires and Terry Johnson from MiniScribe joined with Finis Conner to introduce the 3.5-inch Conner Peripherals, Inc.’s CP340 family in 1987.

By 1989 Conner was the fastest growing company in American history. The 3.5-inch HDD remained the principal size used in PCs for over 25 years, comprising over 80% of the 100 million units shipped in 1996.

The 3.5-inch form factor continues to be used today in both enterprise and personal storage systems that require maximum capacity.