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 |
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 |
correct
incorrect