Shugart Technologies 506

Name of the very first hard disk drive developed for the PC by the company Shugart Technologies, which change its name shortly after to Seagate. It had a 5 MB capacity. A little bit after ST-506 was released this company released its ST-412 model, which had a 10 MB storage capacity.

The technology used by the first PC hard disk drives didn’t have any name at all. Because of that hard drives designed with this technology are simply called ST-506 or ST-412. They are also known as “MFM hard drives” because they used this modulation technique (even though some hard drives from the ST-506 standard used RLL modulation).

The main characteristic from this standard is that the hard disk drive has a controller board. This board really controls the movement of the motors located on the hard drive. The problem is that there is electromagnetic noise in the path between the controller and the hard drive and when this happens the controller must resend the lost command to the hard drive.

Another characteristic from this standard is the use of a stepper motor to move the head unit. Stepper motor is slow and need a command to perform a “step”, i.e. to move the head unit to the next track. For example, 614 commands sent by the controller board are necessary to move the head unit from track 0 to track 614...

Disks from this standard used a technology called coated media, which made the magnetic surface to present problems with the time. Because of that a low-level formatting was necessary from time to time in order to update the hard drive’s bad sector map, which isolates defective spots from the magnetic surface from being used.

Hard disk drives from ST-506 standard were manufactured with capacities from 5 MB to 30 MB. The connection between the hard drive and its controller board used two cables: one for data (34 wires) and another for control (20 wires). Each controller board allowed the connection of up two hard drives. When connecting the second hard drive, the data cable was shared with the first one but the control cable was a separated one.

Hard disk drives from this standard had a maximum transfer rate of 7.5 Mbps (megabits per second), i.e. only 937.5 KB/s.

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