Developed by Seagate. Also known as MFM or RLL since these are the encoding methods used to store data. Seagate originally developed it to support their ST506 (5 MB) and ST412 (10 MB) drives.
34 pin IDC MALE connector at the controller
The first drives used an encoding method called MFM (Modified Frequency Modulation). Later a new encoding method was developed, RLL (Run Length Limited). RLL had the advantage that it was possible to store 50% more with it. But it required better drives. This is almost never an problem. Often called 2,7 RLL because the recording scheme involves patterns with no more than 7 successive zeros and no less than two.
Second connector: 20 PIN IDC MALE at the Controller.
20 PIN IDC FEMALE at the Harddisk.
|2||Head Sel 8|
|4||Head Sel 4|
|14||Head Sel 1|
|18||Head Sel 2|
|26||Drive Sel 1|
|28||Drive Sel 2|
|30||Drive Sel 3|
|32||Drive Sel 4|
Note: All odd pins are GND, Ground.