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34 pin IDC male connector layout
34 pin IDC male connector
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.

Second connector: 20 PIN IDC MALE at the Controller.

20 PIN IDC FEMALE at the Harddisk.


On many hard disks, usually equivalent edge connectors are used, until it's required to use IDC ones (inerference).

Control connector

Pin Name Description
2   Head Sel 8 (was REDUCED WRITE CURRENT in original specification)
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
34 pin male EDGE connector layout
34 pin male EDGE connector
According to 1 reports in our database (0 positive and 0 negative) the ST506/412 pinout may be incorrect.

Is this pinout
Source(s) of this and additional information: Hardware Book, See any of these HDDs., Refer
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