The Free On-line Dictionary of Computing (30 December 2018):
ST-506
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.
Other companies copied the interface, creating a universal de
facto standard that was further strengthened by its revision
to support Seagate's 10 MB ST-412 drive that was adopted for
the IBM PC XT.
Around 1990, SCSI and ATA superseded ST-506.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.
Connector pin-out (http://www.gamesx.com/hwb/co_ST506.html).
(2007-03-06)