The first full-height 5.25 inch hard disk drive for personal computers, introduced in 1980 by Shugart Technology (now Seagate Technology). The ST-506 stored up to 5 megabtyes after formatting using MFM encoding. It transferred data at 625 kilobytes per second.
The ST-506 (like the ST-412) was interfaced to a computer via a disk controller. The interface was a faster version of the Shugart Associates SA1000 interface, which was in turn based upon the floppy disk drive interface. Two cables connected the controller to the disk. The 34-pin control cable controlled mechanical motion and data was read or written serially using two pins of the 20-pin data cable.
Around 1990, SCSI and ATA superseded ST-506. These eliminated the problems of matching controllers to drives by physically integrating a controller with the drive, allowing interleave ratios and other disk parameters to be optimised by the manufacturer rather than the system integrator.