The company was founded in 1979 by Alan Shugart (back from a sabbatical after getting pushed out of Shugart Associates) and Finis Conner; their first product (released in 1980) was the ST-506, the first hard drive to fit the 5.25" form factor of the (by then famous) Shugart "mini-floppy" drive. Sales were good, and the company grew, introducing a 10-megabyte version of the 506, the ST-412, and later developing high-speed drives for the PC/AT; they supplied IBM with drives when it was found that huge numbers of the original PC/AT hard drives, produced by Computer Memories Inc (CMI), were defective.
Through the 1980s, Seagate mainly sold simple drives that were derivatives of (and improvements upon) the original ST-506 design; the ST-225 20MB drive and ST-251 40 MB drive were the biggest sellers of this age, though they also sold faster drives that used voice coil technology. Because of this, Seagate drives were sometimes referred to as cheap and unreliable, a reputation not entirely undeserved because of the 225's and 251's usage of stepper motors to position the heads. However, Seagate drives were usually held in better regard than their competition (mainly MiniScribe, but also Microscience, Rodime, Tandon and Kalok). Seagate finally abandoned stepper motor designs in the early 1990s; the ST351A/X, an oddball 40 MB drive that could run on either an ATA or XT Attachment bus, was their last product to use a stepper.
In 1986, Conner left to start his own hard-drive company, Conner Peripherals, which specialised in small-form-factor drives for portables and (eventually) desktops; Conner also entered the tape drive business with their purchase of Archive. After ten years on their own, Conner rejoined Seagate in a 1996 merger. Also, in 1989, Seagate entered the high-end drive market with their purchase of Control Data's MPI/Imprimis disk storage division.
In 1992, Seagate introduced the Barracuda, the industry's first hard drive with a 7200 RPM spindle speed. They followed this with the Cheetah (the first 10,000 RPM drive) in 1996 and the X15 (15,000 RPM) in 2000. They also introduced the Medalist Pro 7200 range, the first ATA drives with a 7200 RPM spindle, in 1997.