ST506/412

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.
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.

34 PIN IDC MALE (At the controller)
20 PIN IDC MALE (At the controller)

34 PIN IDC FEMALE (At the harddisk)
20 PIN IDC FEMALE (At the harddisk)

34 PIN IDC MALE at the Controller.
20 PIN IDC MALE at the Controller.

34 PIN IDC FEMALE at the Harddisk.
20 PIN IDC FEMALE at the Harddisk.

Control connector

Pin	Name	Description
2		Head Sel 8
4		Head Sel 4
6		Write Gate
8		Seek Complete
10		Track 0
12		Write Fault
14		Head Sel 1
16	RES	(reserved)
18		Head Sel 2
20		Index
22		Ready
24		Step
26		Drive Sel 1
28		Drive Sel 2
30		Drive Sel 3
32		Drive Sel 4
34		Direction In

Note: All odd pins are GND, Ground.

Data connector

Pin	Name	Description
1		Drive Selected
2	GND	Ground
3	RES	(reserved)
4	GND	Ground
5	RES	(reserved)
6	GND	Ground
7	RES	(reserved)
8	GND	Ground
9	RES	(reserved)
10	RES	(reserved)
11	GND	Ground
12	GND	Ground
13		Write Data+
14		Write Data-
15	GND	Ground
16	GND	Ground
17		Read Data+
18		Read Data-
19	GND	Ground
20	GND	Ground